Photochromism of dihydroindolizines. Part 12: synthesis and photochromism of novel π-conjugated rigid dihydroindolizines as potential molecular electronic devices

Article abstract of DOI:10.1016/j.tet.2008.12.047

Novel carbon-rich photochromic dihydroindolizine DHI derivatives and new spirocyclopropenes have been synthesized. Three alternative synthetic pathways for the synthesis of DHI 10 have been established. Different Sonogashira-mediated coupling reactions ha

Full text of DOI:10.1016/j.tet.2008.12.047

Tetrahedron 65 (2009) 1373–1388
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Photochromism of dihydroindolizines. Part 12: synthesis and photochromism
of novel
p-conjugated rigid dihydroindolizines as potential molecular
electronic devices
*
Saleh Abdel-Mgeed Ahmed
Chemistry Department, Faculty of Science, Assiut University, 71516 Assiut, Egypt
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel carbon-rich photochromic dihydroindolizine DHI derivatives and new spirocyclopropenes have
been synthesized. Three alternative synthetic pathways for the synthesis of DHI 10 have been estab-
lished. Different Sonogashira-mediated coupling reactions have been applied to optimize the reaction
conditions and to obtain the best yields. Palladium-mediated Sonogashira coupling of DHIs with
4-(thioacetyl)iodobenzene 13 and iodobenzene 17 yielded coupling products, which have potential ap-
plications in molecular electronics. Irradiation of photochromic DHIs 10a–f, 12a–f, 14a–f, 16a–f and 18a–f
with polychromatic light leads to betaines 9a–f, 13a–f, 15a–f, 17a–f and 19a–f. The coloured betaine
forms are obvious in CH2Cl2 solution with concentration of 1ꢀ10ꢁ5 mol/L at room temperature because
of their slower 1,5-electrocyclization. All the absorption maxima of the coloured betaines were found to
be in the visible region and lie between 524 (betaine 9a) and 639 nm (betaine 15f). The kinetics of the
thermal 1,5-electrocyclization was studied using multichannel UV–vis spectrophotometry. The kinetic
measurements showed that the half-lives of the coloured betaines are in the second domain and lie
between 112 and 1379 s. A highly pronounced increase in the half-lives of betaines bearing dimethyl
substituted pyridazine compared with non-substituted pyridazine betaines was monitored. A large in-
crease in the photostability of both DHIs and betaines under investigation compared with the standard
DHI was observed. The charged zwitterionic betaine structures were stabilized by increasing the solvent
polarity due to the electrostatic interactions between them. The tuning of the absorption maxima and
the kinetic properties by changing the substitution in the fluorene part (region A) and pyridazine part
(region C) will help these compounds to find their applications.
Received 9 September 2008
Received in revised form 26 November 2008
Accepted 11 December 2008
Available online 24 December 2008
Keywords:
Photochromism
Dihydroindolizine (DHI)
Sonogashira coupling
Molecular devices
Photostability
Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction
process is called photochromism. In these systems, the changes in
the electronic patterns responsible for the changes in colour also
Molecules that respond to the application of external stimuli by
undergoing reversible transformations between two distinct
structures have the potential to significantly influence the de-
velopment of numerous important materials science and structural
biology technologies.1,2 This potential is based on the fact that,
because the molecules typically undergo dramatic changes in their
electronic and topological characteristics, they can act as switching
elements and other dynamic components in various optoelectronic
devices and functional materials. Compounds that interconvert
between different isomers having unique absorption spectra when
stimulated with light are referred to as photochromic and the
result in variations in other practical physical properties such as
luminescence,3–7 electronic conductance,8,9 refractive index,10–13
optical rotation14–16 and viscosity.17,18 The photomodulation of
these properties has the potential to significantly advance opto-
electronic technologies such as waveguides,19,20 read/write/erase
optical information storage systems21 and actuators.22,23
If organic photochromic compounds are to find widespread use
in photonic device applications such as erasable memory media
and optical switching, several mandatory properties must be met.
Foremost are thermal irreversibility, photo-fatigue resistance and
high efficiency in rapid photoconversion processes.24 An addi-
tional factor that cannot be downplayed is the ability to tailor the
physical and chemical properties of the photochromic backbone in
a facile, flexible and modular manner. This can only be accom-
plished by designing photochromic compounds that possess many
different locations on their molecular skeletons where functional
groups can be anchored.25
* Present address: Chemistry Department, Faculty of Science, Taibah University,
30002 Al-Madena Al-Mounwara, Saudi Arabia. Tel.: þ20 882333555; fax: þ20
882342708.
E-mail address: saleh_63@hotmail.com
0040-4020/$ – see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2008.12.047

1374
S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
Photochromic dihydroindolizines were discovered and de-
obtain new properties and applications. In continuation of our re-
search on the synthesis and photochromic behaviour of photo-
chromic dihydroindolizines (DHIs), this manuscript will shed more
light on the synthesis and photophysical properties of carbon-rich
fluorenyldihydroindolizine derivatives with molecular wire type
substituents, which are designed to facilitate anchoring of the
molecules to metal substrates and study their photochromic be-
haviour in solution.
veloped by Du¨rr26,27 and are well-known photochromic materials
that have been attracting much interest from the viewpoints of
both fundamental elucidation of electrocyclization reactions
(Scheme 1) and their potential applications in optical memories
and switches.28–32 These materials, based on the 1,5-electro-
cyclization between two distinct isomeric states: ring-open form
(betaine form) and ring-closed form (DHI form), are promising
candidates for optical storage media and electronic devices.33,34
2. Results and discussion
R3
R2
R4
R
R4
2.1. Synthesis of fluorenylacetylene spirocyclo-propene
precursors
R5
C
R1
R
R5
R
X
R
R
R3
X
hν
N +
N
C
A
A
X
X
Spirocyclopropene 7a (n¼0) was previously synthesized by us48
via five steps in 22% yield. Spirocyclopropenes 7b (n¼1) and 7c
(n¼2) were accomplished also in five steps, starting with the lit-
erature conversion of fluorene to 2,7-dibromo-9H-fluoren-9-one in
56% yield over three steps30 (Scheme 2). The following Sonogashira
coupling of 2,7-dibromo-9H-fluoren-9-one with 2b (n¼1) and 2c
(n¼2) in the presence of Pd(PPh)3Cl2 (5 wt %)/CuI/Et2NH in THF at
room temperature for 24 h afforded the coupling products 3b (n¼1)
and 3c (n¼2) in 61 and 53% yield, respectively. Interestingly, con-
densation of compounds 3b,c with hydrazine hydrate in boiling
ethanol for 6 h leads not to the formation of the corresponding
condensation products but to the condensation demethylsilylation
products 4b and 4c in 41 and 39% yield, respectively.
Oxidation of the hydrazone derivatives 4b,c with manganese
dioxide and/or mercuric oxide in dry ether at room temperature in
the absence of light afforded fluorenes 5b,c in moderate yield (53
and 51%, respectively). Addition of methyl acetylene-dicarboxylate
(MADC) to the 9-diazofluorene derivatives 5b,c in dry ether in dark
condition for 24 h led to the formation of 6b and 6c in poor yield
(33 and 29%, respectively).
B
Δ
R1
R2
R1
B
R1
R
R
R
Scheme 1. Schematic representation of the photo-induced ring opening of the DHI
(the three regions A, B and C are represented) to the corresponding coloured betaine.
In the last decade, research on the synthesis of carbon-rich or-
ganic and organometallic compounds for widespread applications
in the field of materials science has remarkably increased. In this
context, the use of p-conjugated rigid fluorenyl chromophores and
their derivatives offers exciting perspectives for the design of new
molecular oligomeric and polymeric materials for various opto-
electronic applications.35 Molecular electronics is currently a topic
of considerable interest among a diverse community of scientists
and engineers as well as the general population and popular
press.35 Much effort and capital have been expended to improve
and further miniaturize the components of computers. The
methods currently used to make the microchips have been com-
mercially scaled down to 0.13 mm (130 nm) feature size (in-
terconnect metal line width, for instance). The lower limit is
expected to be about 30 nm.36 Experts in the semiconductor field
estimate that this limit will be reached in 10–15 years.36
Photolysis of the pyrazole derivatives 6b,c with a high pressure
mercury lamp (125 W) in dry ether solution for 2 h under a nitro-
gen atmosphere gave the target spirocyclopropene derivatives 7b
and 7c in very low yield (15 and 13%, respectively).
If electronics and computer components are to continue de-
creasing in size beyond the 30 nm limit, new technologies must be
invented and explored. Molecular scale devices are logical ap-
proaches to reduce the size of current electronic devices. Self-as-
sembled monolayers (SAMs) of molecular scale wires can achieve
ordering of approximately 1014 molecules/cm2, seven orders of
magnitude greater. Also, one can manufacture 1 mol of these
molecules in a large laboratory flask, which amounts to 6ꢀ1023
devices, or more than the number of transistors ever made in the
history of the world.37–42 It is for these reasons and others that
work continues in the development of molecular electronic can-
didates. Of course, there are numerous problems that need to be
solved before molecular computing is realized, including address-
ing single molecules in circuits and the need for heat dissipation at
these packing levels.38 Many molecular structures have been syn-
thesized for use as molecular devices, including switches, wires,
controllers and gates.39–43
2.2. Different attempts for the synthesis of
photochromic dihydroindolizines 10a–f
p-conjugated
Photochromic DHI 10a (R¼H, n¼0) was previously synthesized
by us.48 Nucleophilic addition of pyridazines 8a,b to spiro-
cyclopropenes 7b,c using the cyclopropene route26,30 (Scheme 3) in
dry ether solution at room temperature under dry nitrogen in the
absence of light (TLC controlled using CH2Cl2 as eluent) led to the
formation of the photochromic dihydroindolizines (DHIs) 10b–f in
low yield (14–24%, method A, Table 1). The reaction occurred
through electrophilic addition of the electron-deficient spiro-
cyclopropenes 7b,c to the nitrogen of the N-heterocyclic pyr-
idazines 8a,b, which led to ring opening via a cyclopropyl-allyl
conversion 90b–f to the coloured betaines 9b–f (Scheme 3). A
subsequent ring closure to DHIs 10b–f results in a partial slow
thermal 1,5-electrocyclization back reaction (Scheme 3), which can
be reversed upon exposure to light. Pure photochromic DHIs 10a–f
were obtained by column chromatography on silica gel using
dichloromethane as the eluent.
Another successful alternative method for the synthesis of the
target photochromic DHIs 10b–f was achieved through the fol-
lowing synthesis (Scheme 4, Table 1). The Sonogashira coupling of
11a and 11b (which were previously prepared by us30) with 2a–c in
the presence of palladium diphenylphosphinedichloride (5%) and
CuI/Et3N in dry THF yielded the desired photochromic trime-
thylsilyl DHIs 12a–f in 34–23% yield after purification by flash
chromatography on silica gel and CH2Cl2 as eluent (method B).
Within contemporary acetylene chemistry44 there is great in-
terest in the synthesis of conjugated diyne and oligoyne molecules.
They are fundamentally important carbon-rich building blocks45
for molecular rods and cyclic frameworks and they are active
components in optoelectronic devices (wires, switches, non-linear
optics, etc.)46 and the extent of intramolecular ð-conjugation
within the diyne is a topic of experimental and theoretical debate.47
Recently, we succeeded in the design and synthesis of a carbon-
rich photochromic dihydroindolizine by using many coupling re-
action conditions.48 The novel synthesized target molecules may
have applications in the field of optoelectronics and non-linear
optics. These results motivated us to explore the synthesis of more
novel, rigid, carbon-rich fluorenyldihydroindolizines aiming to

S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
1375
H
SiMe3
n
n
SiMe3
n
Br
NH2NH2
Ethanol
Pd(PPh3)2Cl2
Cu2I2 / Et3N
N-NH2
O
+
O
Br
1
H
2a, n= 0
2b, n= 1
2c, n= 2
SiMne3
3a, n= 0
3b, n= 1
3c, n= 2
n
H
4a, n= 0
4b, n= 1
4c, n= 2
H
H
n
H
n
n
COOCH3
N
hν
MADC
N
MnO2
Ether
N2
Ether
Ether
COOCH3
COOCH3
COOCH3
n
n
n
H
H
H
7a, n= 0
7b, n= 1
7c, n= 2
5a, n= 0
5b, n= 1
5c, n= 2
6a, n= 0
6b, n= 1
6c, n= 2
Scheme 2. Preparation outline of spirocyclopropene precursors 7a–c.
H
H
n
H
H
n
n
n
R
R
R
+
COOCH3
R
N
N
R
COOCH3
+
R
+
N
N
Ether
24h/RT
-
Δ
COOCH3
N
N
-
N
N
hν
R
R
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
8a, R=H
8b, R=CH3
n
n
n
H
9`a-f
n
H
H
H
9a-f
10a-f
7a, n= 0
7b, n= 1
7c, n= 2
Scheme 3. Method (A) for preparation outline of photochromic DHIs 10a–f from spirocyclopropenes 7b,c.

1376
S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
Table 1
rigid acetylenic bridged DHIs 10a–f could be successfully prepared
through three reactions pathways as shown in Scheme 4. The three
products obtained from the different pathways showed the same
analytical and exactly the same spectroscopic data as well as the
same melting points (mp) and mixing melting points (mmp) (Table 1).
Substituent patterns, yields and melting points of the target photochromic DHIs
(10a–f) synthesized by three pathways A, B and C
DHI 10
R
n
Method
Yield (%)
Mp (ꢂC)
a
a
a
b
b
b
c
c
c
d
d
d
e
e
e
f
H
H
H
H
H
H
H
H
0
0
0
1
1
1
2
2
2
0
0
0
1
1
1
2
2
2
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
24
68
43
20
56
40
16
51
39
18
46
36
17
45
32
14
44
30
152–153
152
151–152
143
142–143
142
116
115–116
114–115
122
122
121
112
111–112
112
98
99–100
98
2.3. Palladium-mediated Sonogashira coupling of
photochromic DHIs 10a–f with aryl halothioethers 13 and
haloaryl 17 under different reaction conditions
The final coupling of the photochromic DHIs 10a–f to thioester
1347 and iodobenzene 17 was planned via a palladium-mediated
Sonogashira coupling (Scheme 5). Because of the strong affinity of
sulfur containing groups, especially free thiols, for transition metals
like palladium, the protection of the sulfur atoms is mandatory.49 In
the past, the coupling of alkynes with palladium in the presence of
thioacetate functionalities was successfully achieved by several
groups.50,51
H
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
f
f
Reaction of DHIs 10a–f with 2 mol of 4-(thioacetyl)iodobenzene
13 under standard Sonogashira conditions (3% Pd(PPh3)Cl2, 10%
PPh3, 5% CuI/NEt3, THF, 18 h at 45 ꢂC, method A) gave low conver-
sions to the coupling products 14a–f (17–23% yield, method A). Al-
ternative conditions for the Sonogashira coupling, using Pd(OAc)2,
triphenylphosphine and 10% CuI, NEt3, toluene, DMF (3:1) for 12 h at
40 ꢂC (method B) gave 14a–f in better yields (27–38%). Aiming to
Treatment of DHIs 12a–f with tetrabutyl ammonium fluoride
(TBAF) in dry THF for 17 h afforded the desilylated products 10a–f
in 44–68% yield (Table 1).
Alternatively, deprotection could be achieved with hydrazine
hydrate to give 10a–f in 30–43% yield (method C, Table 1). Thus,
SiMe3
H
n
n
SiMe3
n
R
Br
R
R
R
N
Pd(PPh3)2Cl2
N
TBAF/ THF
(Method B)
R
R
+
N
N
Cu2I2 / Et3N
N
N
COOCH3
Br
11a, R= H
COOCH3
COOCH3
COOCH3
COOCH3
COOCH3
n
n
H
11b, R= CH3
2a, n= 0
2b, n= 1
2c, n= 2
SiMe3
12a-f
H
10a-f
Δ
NH2NH2
Ethanol
(Method C)
hν
hν
Δ
H
n
H
H
n
n
COOCH3
R
COOCH3
+
N
R
+
N
-
N
N
-
N
N
COOCH3
COOCH3
COOCH3
COOCH3
n
n
n
H
H
9a-f
H
10a-f
13a-f
Scheme 4. Method (B,C) of the reaction pathways for the synthesis of the target photochromic DHIs 10a–f.

S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
1377
Table 2
SAc
Substituents pattern, yields and melting points of the photochromic DHIs (14a–f,
16a–f and 18a–f) synthesized through palladium-mediated Sonogashira coupling
n
DHI
R
n
Method
Yield (%)
Mp (ꢂC)
H
n
14a
14a
14a
14b
14b
14b
14c
14c
14c
14d
14d
14d
14e
14e
14e
14f
H
H
H
H
H
H
H
H
0
0
0
1
1
1
2
2
2
0
0
0
1
1
1
2
2
2
0
1
2
0
1
2
0
1
2
0
1
2
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
A
B
C
C
C
C
C
C
C
C
C
C
C
C
C
23
37
52
21
38
47
20
30
47
18
29
45
18
27
44
17
27
43
63
64
60
56
54
46
40
42
43
39
35
30
112
112–113
113
100
99
99–100
86
88
R
R
I
SAc
R
R
N
N
N
N
13 (2 mole)
H
87
Pd/Cu/THF
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
CH3
H
H
H
CH3
CH3
CH3
H
102
102
101
84
82
80
72
71
71
143
136
130
118
110
98
129
118
102
113
90
COOCH3
COOCH3
COOCH3
COOCH3
n
n
14f
14f
H
16a
16b
16c
16d
16e
16f
18a
18b
18c
18d
18e
18f
10a-f
SAc
14a-f (betaine form 15a-f)
Pd/Cu/THF
I
SAc
13 (1 mole)
H
H
CH3
CH3
CH3
H
n
n
83
above mentioned Sonogashira-coupling conditions (method C) led
to the formation of the coupling products of the photochromic DHIs
18a–f in 30–43% yield (Table 1). Analysis of 14c through a NOESY
experiment and MM2 (Fig. 1) suggests that the pyridazine moiety is
perpendicular to the fluorene skeleton, which explained the cou-
pling between the pyridazine and fluorene protons observed in this
system.
R
R
I
R
N
N
R
N
N
17
Pd/Cu/THF
COOCH3
COOCH3
COOCH3
COOCH3
n
n
2.4. Photophysical properties of the newly synthesized
carbon-rich photochromic DHIs 10a–f, 12a–f, 14a–f, 16a–f and
18a–f, and their corresponding betaines 9a–f, 13a–f, 15a–f,
17a–f and 19a–f in dichloromethane solution at 23 8C
2.4.1. Absorption spectra of DHIs 9, 11, 14, 16 and 18, and their
corresponding betaines 8, 12, 15, 17 and 19
SAc
SAc
16a-f (betaine form 17a-f)
18a-f (betaine form 19a-f)
Photophysical data pertinent to their photochromic properties
were obtained from the absorption features of photochromic DHIs
10a–f,12a–f,14a–f,16a–f and 18a–f. Electronic spectra of the newly
synthesized DHIs 10a–f, 12a–f, 14a–f, 16a–f and 18a–f were mea-
sured in dichloromethane solution using a UV–vis spectropho-
tometer with concentration of 1ꢀ10ꢁ5 mol/L at 23 ꢂC. All studied
DHIs 10a–f, 12a–f, 14a–f, 16a–f and 18a–f are yellow in the solid
state and in dichloromethane solution (Table 3). The intensities
Scheme 5. Palladium-mediated Sonogashira coupling of DHI 10a–f with 4-(thio-
acetyl)iodobenzene 13 and iodobenzene 17.
improve the coupling product yield of 14a–f, the reaction conditions
were changed to use bis(dibenzylideneacetone)palladium(0), 10%
CuI, triphenylphosphine and DIEA inTHFat 40 ꢂC for 3 h (method C),
which led tothe formation of the coupling products 14a–f in 43–52%
yield. In addition, coupling of photochromic DHIs 10a–f with 2 mol
of 4-(thioacetyl)iodobenzene 13 using 1,0-phenathroline/NaI, CuI,
DMF and TEA at 110 ꢂC (method D) did not afford the coupling
products 14a–f (Table 2).
The above mentioned reaction conditions have been applied to
the reaction of DHIs 10a–f with 1 mol of 4-(thioacetyl)iodobenzene
13 in order to synthesize the desired monocoupling products 16a–f.
The best reaction conditions with the highest yield was found when
using bis(dibenzylideneacetone)palladium(0), Cu2I2, triphenyl-
phosphine and DIEA in THF at 40 ꢂC for 3 h (method C), which led to
the formation of the coupling products 16a–f in 46–64% yield.
Further coupling of DHIs 16a–f with iodobenzene 17 under the
(log 3) of these bands were found to be between 3.90 and 4.53
depending on the number of alkyne groups. The absorption of DHIs
10a–f, 12a–f, 14a–f, 16a–f and 18a–f was observed in the far UV
region and showed absorption maxima between 388 and 399 nm
(Table 3). This absorption is dependent on the number of phenyl-
ethyne (n) substituents on the fluorene (region A). A pronounced
bathochromic shift after coupling with 4-(thioacetyl)iodobenzene
and iodobenzene as in DHIs 14a–f, 16a–f and 18a–f by about 10 nm
was recorded. This may be attributed to the increasing aromaticity
of the conjugated DHI skeleton after coupling reaction. Methyl
substituents in the pyridazine region could not influence the ab-
sorption maxima of the DHI system. As established previously,26–34

1378
S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
Figure 1. Representation of the optimized (MM2) structure of DHI 14c.
these absorption bands can be assigned to the locally excited (LE)
transition located in the butadienyl-vinyl-amine chromo-
forms, which contain a dimethyl pyridazine substituents in region C
(i.e., 9d–f, 13d–f, 14d–f, 17d–f and 19d–f) exhibit a green-blue
colour and show three absorption maxima between three iso-
sbestic points (Table 3). The existence of the three isosbestic points
proves that the thermal back reaction of the coloured betaines
follows the first order reaction. Interestingly, a bathochromic shift
of the absorption of the betaines containing non-substituted pyr-
idazines 9a–c, 13a–c, 14a–c17a–c and 19a–c by more than 100 nm
in the visible region compared with the betaines with dimethyl
substituted pyridazines 9d–f, 13d–f, 14d–f, 17d–f and 19d–f was
recorded. This big shift led to the change of the coloured forms from
red to green-blue and can be attributed to the electron donating
abilities of the two methyl groups. These stabilized the zwitterionic
betaines, hence causing the bathochromic shift of the coloured
betaine absorptions in the visible region30 (Table 3). Furthermore,
a noticeable bathochromic shift of about 5–7 nm was observed
upon increasing the number of bridged phenyl acetylenic groups
from n¼0 to n¼3 with no dependency on the substituted or non-
p–
p
*
phores29–34 of DHIs 10a–f, 12a–f, 14a–f, 16a–f and 18a–f (Table 3).
Irradiation of DHIs 10a–f, 12a–f, 14a–f, 16a–f and 18a–f with
polychromatic light leads to ring open betaines 9a–f, 13a–f, 15a–f,
17a–f and 19a–f (Fig. 2). The coloured betaine forms 9a–f, 13a–f,
15a–f, 17a–f and 19a–f varied from red to blue-green; their col-
ouration is obvious in CH2Cl2 solution with a concentration of
1ꢀ10ꢁ5 mol/L at room temperature because of their slower 1,5-
electrocyclization, which refers to the stabilization of the charged
zwitterionic betaines affected by the heterocyclic pyridazine moi-
ety. All the absorption maxima of the coloured betaines 9a–f, 13a–f,
15a–f,17a–f and 19a–f were found to be in the visible region and lie
between 524 (betaine 9a) and 639 nm (betaine 15f). The UV spectra
of the coloured betaines containing a pyridazine as a heterocyclic
moiety in region C (i.e., 9a–c, 13a–c, 14a–c, 17a–c and 19a–c) (Fig. 2)
exhibit a red colour and show only one absorption maximum
ranged between 524 and 537 nm. On the other hand, the betaine
Table 3
UV–vis absorption DHIs 10a–f, 12a–f, 14a–f, 16a–f and 18a–f, and their corresponding betaines 8, 12, 15, 17 and 19, and kinetic data of betaines 9a–f, 13a–f, 15a–f, 17a–f and
19a–f in the s range (recorded by UV spectrophotometer) in CH2Cl2 solution (23 ꢂC, c¼1ꢀ10ꢁ5 mol/L)
DHI/betaine
lmax (DHI) [nm]
log
3
lmax (betaine) [nm]
kꢀ10ꢁ3 (sꢁ1
)
t1/2 (s)
Colour of betaine
10a/9a
10b/9b
10c/9c
10d/9d
10e/9e
10f/9f
388
392
397
393
395
398
390
392
393
394
398
398
390
394
398
395
397
398
388
395
397
394
396
398
388
388
390
394
396
397
3.90
3.93
4.07
4.10
4.15
4.19
3.91
3.94
4.00
4.14
4.17
4.19
4.12
4.22
4.27
4.14
4.19
4.25
3.92
3.97
4.09
4.10
3.96
4.09
4.16
3.94
3.99
4.09
4.12
4.22
524
527
530
352, 447,627
356, 447,629
350, 445,631
525
528
532
353, 448,628
358, 448,629
353, 446,632
529
533
538
357, 448,633
358, 448,634
353, 446,639
526
528
529
354, 442,630
358, 446,632
352, 447,636
528
532
537
355, 447,632
357, 447,633
358, 448,635
6.19
4.85
3.50
0.99
0.71
0.62
5.98
4.65
3.71
0.97
0.95
0.57
4.15
3.54
2.85
0.86
0.74
0.50
4.95
4.15
3.50
0.99
0.88
0.70
4.25
3.54
2.85
0.86
0.74
0.50
112
143
198
698
980
1112
116
Red
Red
Red
Blue-green
Blue-green
Blue-green
Red
Red
Red
Green
Green
Green
Red
Red
Red
Green-blue
Green-blue
Green-blue
red
red
red
Green-blue
Green-blue
Green-blue
Red
Red
Red
Green-blue
Green-blue
Green-blue
12a/13a
12b/13b
12c/13c
12d/13d
12e/13e
12f/13f
14a/15a
14b/15b
14c/15c
14d/15d
14e/15e
14f/15f
16a/17a
16b/17b
16c/17c
16d/17d
16e/17e
16f/17f
18a/19a
18b/19b
18c/19c
18d/19d
18e/19e
18f/19f
149
187
712
998
1202
167
196
243
806
937
1379
140
167
198
703
786
984
163
196
243
806
937
1379

S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
1379
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
2.5
DHI form
Betaine form
Betaine
537 nm
2.0
390 nm
DHI
1.5
1.0
0.5
0.0
527 nm
388 nm
300
400
500
Wavelength (nm)
600
700
800
300
400
500
Wavelength (nm)
600
700
800
Figure 2. UV–vis of photochromic DHI 18c and the corresponding betaine form 19c
after UV irradiation in CH2Cl2 (c¼1ꢀ10ꢁ5 mol/L) at ambient temperature.
Figure 4. Kinetic FT-UV–vis spectrum of the thermal fading of betaine 19c to DHI 18c
(cycle time¼90 s, run time¼900 s) in CH2Cl2 (c¼1ꢀ10ꢁ5 mol/L at 253 K).
fluorene moiety. Also, a noticeable increase in the half-lives of the
betaines coupled with thioacetyl groups as in 15a–f, 17a–f and 19a–
f compared with non-coupled betaines was observed. This tuning
of the absorption maxima and the kinetic properties by changing
the fluorene substitution (region A) as well as in the pyridazine
(region C) will help this family of compounds to find many appli-
cations particularly in the area of molecular electronics.
substituted pyridazine. This may be attributed to the increasing
aromaticity of the fluorene unit conjugated with the aromatic
phenyl rings through the bridged acetylenic bond. More spectro-
scopic data about the UV–vis measurements of the coloured beta-
ines under investigation are listed in Table 3.
The kinetics of the thermal 1,5-electrocyclization was studied by
using multichannel FT-UV–vis spectrophotometry (Figs. 3–5). The
kinetic measurements showed that the half-lives of the coloured
betaines 9a–f, 13a–f, 15a–f, 17a–f and 19a–f are in the second do-
main and lie between 112 and 1379 s (Table 3, Figs. 3–5). A highly
pronounced increase in the half-lives of the betaines bearing a di-
methyl substituted pyridazine (9d–f, 13d–f, 14d–f, 17d–f and
19d–f) by approximately a factor of 6 was observed compared with
the half-lives of the betaines bearing a non-substituted pyridazine
(9a–c,13a–c,14a–c,17a–c and 19a–c). This increase in the half-lives
may be attributed to the stabilization of the electrostatic charges on
the betaines by the electron donating methyl groups. An increase of
the half-lives of the betaines by increasing the number of acetylenic
bridges from one to three acetylenic bridges in the fluorene part by
approximately a factor of 1.25 was recorded. This may be attributed
to the bulky sterically hindered phenyl rings substituted by the
2.4.2. Photo-fatigue resistance of photochromic DHIs 10a–f, 12a–f,
14a–f, 16a–f and 18a–f, and their corresponding betaines 9a–f,
13a–f, 15a–f, 17a–f and 19a–f in dichloromethane solution
(c¼1ꢀ10ꢁ5) at 253 K
In studying the quality of a photochromic system the problem of
carrying out a large number of colourization–decolourization cy-
cles arises frequently. The gradual loss of the ability to change
colour by exposure to visible or ultraviolet light in this context has
been termed fatigue.1 Gautron51 has advanced a quantitative ap-
proach to measure the fatigue in photochromic systems.
Due to the slow thermal bleaching process of the betaines to
DHIs, a temperature FT-UV–vis measurement was used in this case.
2.1
524 nm
398 nm
1.8
446 nm
1.8
1.5
1.5
639 nm
390 nm
1.2
1.2
353 nm
0.9
0.9
0.6
0.3
0.0
0.6
0.3
0.0
300
300
400
500
600
700
Wavelength (nm)
800
900
1000
400
500
Wavelength (nm)
600
700
800
Figure 5. Kinetic FT-UV–vis spectrum of the thermal fading of betaine 15f to DHI 14f
(cycle time¼90 s, run time¼3600 s) in CH2Cl2 (c¼1ꢀ10ꢁ5 mol/L at 253 K).
Figure 3. Kinetic FT-UV–vis spectrum of the thermal fading of betaine 13a to DHI 12a
(cycle time¼60 s, run time¼600 s) in CH2Cl2 (c¼1ꢀ10ꢁ5 mol/L at 253 K).

1380
S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
Table 4
Photodegradation data of some selected betaines 9a–f, 15a–f, 17a–f and 19a–f in
2.6
2.4
2.2
2.0
1.8
1.6
1.4
Betaine (colored form)
dichloromethane solution (c¼1ꢀ10ꢁ5 mol/L) at 23 ꢂ
C
Betaines
t30-Betaine/DHI (min)
F
Betaines t30-Betaine/DHI (min)
F
9a
9b
9c
9d
9e
9f
15a
15b
15c
15d
15e
15f
471
423
359
521
486
412
475
458
424
493
476
453
1.94 17a
1.74 17b
1.48 17c
2.14 17d
2.00 17e
589
542
513
675
624
525
599
546
534
698
664
603
243
2.42
2.23
2.11
2.78
2.57
2.16
2.47
2.25
2.20
2.87
2.73
2.48
1.00
1.70
17f
1.95 19a
1.88 19b
1.74 19c
2.03 19d
1.96 19e
1.86
19f
Standard 243
1.00 243
DHI (colorless form)
0
5
10
15
20
25
Bleaching/Fading Cyles
30
35
40
Irradiation of degassed dichloromethane solution of DHIs 10a–f,
12a–f, 14a–f, 16a–f and 18a–f at room temperature (23 ꢂC) with
polychromatic light (
l
¼200–400 nm) produced the coloured be-
Figure 7. Cycling of the bleaching and fading of DHI 18b and betaine 19b (irradiation/
thermal fading/irradiation cycles) in CH2Cl2 (c¼1ꢀ10ꢁ5 mol/L) at ambient temperature.
taines 9a–f, 13a–f, 15a–f, 17a–f and 19a–f. Upon continued irradi-
ation they decomposed after sometime. However, if oxygen is
excluded, these systems are noticeably more stable. It is possible
that in the presence of oxygen, betaines 9a–f, 13a–f, 15a–f, 17a–f
and 19a–f act as sensitizers towards singlet oxygen.1
pyridazine moiety, showed the highest photo-fatigue resistance by
a factor of about 0.3 amongst the other studied betaines and also by
a factor of 1.87 compared with the standard betaine (t30¼243 min).
This betaine can now be used as the new standard in the photo-
degradation measurements in the photochromic dihy-
droindolizines family.
Figure 7 represents an interesting property of the bleaching/
fading of the DHI 18b and betaine 19b. These cycles of DHI/betaine
showed that after irradiation and thermal fading, no decomposition
product could be observed by UV–vis measurements. This result is
corroborated by NMR measurements, which showed similar NMR
The photodegradation data represented in Table 4 and Figure 6
show that most of the selected betaines under investigation
showed a higher photo-fatigue resistance than the standard
dicyano-pyridazine DHI (t30¼243 min) by a factor of 1.48 in the case
of betaine 9c, and 2.87 in the case of betaine 19d. A noticeable
decrease of the t30 values by increasing the number of acetylenic
bridges in both betaines bearing two methyl groups and the non-
substituted pyridazine was recorded. A highly pronounced increase
of the t30 values of the betaines incorporating dimethyl pyridazine
as in betaines 9d–f, 15d–f, 17d–f and 19d–f compared with the
betaines incorporating non-substituted pyridazine as in betaines
9a–c, 15a–c, 17a–c and 19a–c by factor of about 0.4 has been ob-
served. Interestingly, betaines 15a–f and 19a–f, which have po-
tential molecular electronic applications, showed the highest t30
values compared with other betaines under investigation. Betaine
19d (t30¼698 min), substituted with two methyl groups in the
spectra (coupling,
d values and integration) of the DHI before ir-
radiation and after 20 cycles of irradiation with no detection of any
decomposed products.
2.4.3. Solvatochromism
It is known that the UV–vis-absorption spectra of chemical
compounds may be influenced by the surrounding medium and
that solvents can bring about a change in the position, intensity and
shape of absorption.52,53
Generally, a strong effect of the solvent polarity on the lmax and
half-lives of betaines 9a–f, 13a–f, 15a–f, 17a–f and 19a–f was ob-
served. For example, changing the solvent from tetrahydrofuran to
methanol leads to a hypsochromic shift ranged between Dnyþ790
and Dnyþ1120 cmꢁ1 in absorption in the visible region. These two
betaine9a
betaine9b
betaine9c
betaine9d
betaine9e
betaine9f
100
80
60
40
20
0
betaine15a
betaine15b
betaine15c
betaine15d
betaine15e
betaine15f
Table 5
Half-lives (t1/2) of thermal 1,5-electrocyclization of selected betaines 9a, 13f, 15c,15e,
17c, 17d, 19a, 19d and 19f, and ET(30) values of 10 different solvents recorded by
kinetic UV–vis technique (c¼1ꢀ10ꢁ5 mol/L) at ambient temperature
Solvents
Betaines t1/2 (s)
ET (30)
9a 13f
15c 15e
17c 17d 19a 19d 19f
n-Pentane
Toluene
45 927 182
90 981 212
745 162 556 134 635 1087 32
769 174 580 139 674 1139 34
Dioxane
103 1039 214 824 183 627 145 701 1201 36
Tetrahydrofuran 107 1099 222 836 187 639 149 734 1247 37
Chloroform 110 1164 237 887 191 673 154 787 1323 39
Dichloromethane 112 1202 243 937 198 712 168 811 1387 41
0
100
200
Photodegradation time (min.)
300
400
500
600
Acetonitrile
2-Propanol
Ethanol
130 1301 298 1067 218 797 189 928 1537 46
136 1464 301 1118 234 844 192 976 1664 49
151 1575 307 1173 256 887 212 1017 1737 52
160 1687 329 1294 284 951 229 1113 1898 56
Figure 6. Time-relative absorbance relationship of the photodegradation experiment
for determination of the t30 value of selected betaines 9a–f and 15a–f in CH2Cl2
(c¼1ꢀ10ꢁ5 mol/L) at ambient temperature.
Methanol

S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
1381
16000
14000
12000
10000
8000
6000
4000
2000
0
spectrum photochromic properties of the new DHIs and their cor-
responding betaines will help to find their suitable applications.
Further studies by supporting of these compounds onto the surface
of metals such as gold, silicon and titanium will be discussed in
detail in the forthcoming paper.
n.Pentane
Toulene
Dioxane
THF
Chloroform
Dichloromethane
Acetonitrile
isopropanol
Ethanol
4. Experimental
4.1. General
Methanol
Spirocyclopropene derivatives 7a–c were obtained via photo-
lysis of the corresponding pyrazoles prepared according to the
reported procedures.54 Photolysis was carried out in the photo-
chemical reactor of Schenck55 made from Pyrex (
l >290 nm). The
source of irradiation was a high pressure mercury lamp Philips HPK
125 W. Dihydroindolizines 11a,b were previously prepared by
us.30a–d Trimethylsilyl acetylene derivatives 2a–c were prepared
following the reaction procedures published by Rodriguez et al.35b
Full characterization of spirocyclopropenes 7a–c will be given in
detail in the forthcoming paper.56 Prior to photolysis, solutions
were flushed with dry nitrogen for 30 min before switching on the
UV lamp. The progress of the reaction and the purity of the prod-
ucts isolated were monitored using TLC. Separation and purifica-
tion of all the synthesized photochromic materials were carried out
using column chromatography (80 cm lengthꢀ2 cm diameter) on
silica gel and CH2Cl2 as eluent. Melting points were determined on
an Electrothermal Eng. Ltd melting point apparatus and are un-
corrected. All NMR spectra were collected on a Bru¨ker DRX 400
spectrometer (400 MHz) in CDCl3 using TMS as the internal stan-
9a
19a
17c
15c
17d
Betaines
19d
15e
13f
19f
Figure 8. Representative diagram showing the influence of differing solvent polarity
on the half-lives (t1/2) of betaines 9a, 13f, 15c, 15e, 17c, 17d, 19a, 19d and 19f recorded
by millisecond flash photolysis technique (c¼1ꢀ10ꢁ5 mol/L) at 23 ꢂC.
solvatochromic shifts are ascribable to
ible region.
p–
p transitions in the vis-
*
A pronounced solvent influence on the half-lives (t1/2) of the
selected betaines 9a, 13f, 15c, 15e, 17c, 17d, 19a, 19d and 19f was
determined using UV–vis techniques at room temperature in 10
different solvents (Table 5). A large increase in the half-lives with
increasing solvent polarity was recorded in all studied betaines 9a,
13f, 15c, 15e, 17c, 17d, 19a, 19d and 19f (Fig. 8). This is mainly at-
tributed to the partial charge transfer from the betaine form to the
solvent and vice versa, as a result of a weak Coulombic-exchange
effect. Therefore, the charged zwitterionic betaine structure was
stabilized by increasing the solvent polarity due to the electrostatic
interactions between them. The tunability of the half-lives in the
different media polarities exhibits the importance of correct sol-
vent selection for specific applications.
dard. Chemical shifts (d) are reported in parts per million. FTIR
measurements were performed using a Perkin Elmer Paragon 1000
instrument. Mass spectra were recorded on a VG AutoSpec appa-
ratus using electronic impact at 70 eV. MALDI-MS spectra were
recorded in the positive mode by using a 2,5-dihydroxy-benzoic
acid in dioxane as matrix. IR spectra were measured on a BIO-Rad
Excalibur series, FTS 3000. UV spectra were recorded on an FT-UV/
VIS JASCO V-570 computerized spectrophotometer. Experimental
details, procedures and full characterizations of the new synthe-
sized DHIs 10a–f, 12a–f, 14a–f, 16a–f and 18a–f are described
below.
4.2. Dimethyl (2,7-diphenylethynyl)n-4a0H-spiro[fluorene-
9,50-pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylates 10a–f:
general procedure
3. Conclusion
Carbon-rich molecules based on photochromic dihydro-
indolizine (DHI) derivatives have been successfully synthesized via
Sonogashira-coupling reactions. The coupling reactions between
fluorenes (region A) and acetylenic bridges resulted in target
molecules with extended photochromism. In addition, new spi-
rocyclopropenes for present and future designing of photochromic
DHIs have been synthesized by both chemical and photochemical
reaction methods. Different attempts towards suitable conditions
for Sonogashira-mediated coupling of the DHI skeleton with
4-(thioacetyl)iodobenzene and iodobenzene have been discussed.
Interesting photochromic properties have been observed by tuning
the chemical structure of the photochromic DHI by changing the
number of acetylenic bridges in the fluorene part and the sub-
stitution in the pyridazine region. This pronounced influence of the
substitutions in both regions A and C showed strong effects on the
UV–vis absorption of DHIs and betaines as well as their kinetic
properties (half-lives). Interestingly, the photochromic DHIs and
their corresponding betaines showed a very strong resistance to
photodegradation through direct irradiation or by cycling between
coloured and closed forms. A pronounced effect of 10 solvents with
different polarities on the photochromism of the synthesized DHIs
and their corresponding betaines has been observed. These broad
Method A. A mixture of spirocyclopropenes 7a–c (1 mmol) in dry
ether (50 mL) and pyridazine 8a (2 mmol) and/or 2,6-dimethyl
pyridazine (2 mmol) were stirred at room temperature under dry
N2 with exclusion of light for 24 h. Ether was removed under re-
duced pressure and the residue was chromatographed twice on
silica gel (dichloromethane). The pure product was obtained after
recrystallization from the appropriate solvents to afford the prod-
ucts as pale yellow crystals.
Method B. To a solution of 2,7-dibromo pyridazine DHIs 11a,b
(1.1 mmol) and trimethylacetylene (0.35 mL, 2.5 mmol) in dry THF
(20 mL) and freshly distilled triethylamine (50 mL) under an argon
atmosphere at 50 ꢂC were added dichloro bis(triphenyl-
phosphine)palladium (39 mg, 0.052 mmol, 5%) and copper iodide
(2.1 mg, 0.015 mmol). The mixture was stirred for 5 h and then the
amine and THF were removed under reduced pressure. The crude
residue was washed with a saturated aqueous ammonium chloride
solution with a little amount of KCN (1% solution, 20 mL) and
extracted with dichloromethane. The extracts were dried over an-
hydrous sodium sulfate and after filtration, the solvent was removed
to give a brown solid, which was purified by silica gel column
chromatography to afford the trimethylated DHIs 12a–f. DHIs 12a–f

1382
S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
(0.28 mmol) were stirred in freshly distilled dry THF (20 mL) with
mixture of tetrabutyl ammonium fluoride (TBAF, 0.300 g,
128.74, 125.28, 124.95, 124.08, 122.47, 121.26, 120.84, 118.90, 104.98,
93.38 (acetylenic-C), 91.61 (acetylenic-C), 82.42 (acetylenic-C),
81.42 (acetylenic-C), 65.36 (80a-C), 63.42 (spiro-C), 53.44 (30-CH3),
a
2.2 mmol) in freshly distilled THF solution (5 mL) at room temper-
ature undera nitrogen atmosphere. Thereaction mixturewas stirred
for 12 h and then water (20 mL) was added. The mixture was
extracted with ethyl acetate (3ꢀ20 mL) and the residue was purified
by column chromatography using dichloromethane as eluent to
afford the required compounds 10a–f as yellow solids.
Method C. A solution of DHIs 12a–f (0.5 mmol) and hydrazine
hydrate (99%, 0.1 mL, 2 mmol) in absolute ethanol (20 mL) was
cooled to 0 ꢂC and stirred at this temperature for 2 h. The solvent
was removed and the product was extracted with ethyl acetate
(3ꢀ20 mL) and the residue was purified by column chromatogra-
phy using dichloromethane as eluent to afford the required com-
pounds 10a–f as yellow solids.
51.37 (20-CH3) ppm; IR (KBr):
n
¼3128–3067 (C-H, arom.), 2830–
2987 (C-H, aliph.), 2152 (acetylenic bond), 1754 (30-C]O), 1683 (20-
C]O), 1598 (C]N), 1457 (C]C), 1348, 1256, 1190, 1097, 954, 889,
773 cmꢁ1; MS-EI m/e (%) 834.25 [Mþ]. Elemental analysis for
C59H34N2O4: C, 84.87; H, 4.10; N, 3.36. Found %: C, 84.88; H, 4.11; N,
3.35.
4.2.4. Dimethyl 2,7-diethynyl-20,4a0-dimethyl-4a0H-spiro[fluorene-
9,50-pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 10d
1H NMR (400 MHz, CDCl3)
d
7.67 (d, J¼1.45 Hz, 1H, CH-arom.),
7.60 (d, J¼8.13 Hz, 2H, CH-arom.), 7.50 (dd, J¼1.55, 2.12 Hz, 1H,
CH-arom.), 7.46–725 (m, 2H, CH-arom.), 5.54 (d, J¼9.73 Hz, 1H, 70-
CH), 5.04 (d, J¼9.71 Hz, 1H, 80-CH), 4.07 (s, 2H, acetylenic-H), 3.95
(s, 3H, 30-CH3), 3.37 (s, 3H, 20-CH3), 2.05 (s, 3H, 60-CH3), 1.48 (s,
4.2.1. Dimethyl 2,7-diethynyl-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-
b]pyridazine]-60,70-dicarboxylate 10a
3H, 80-CH3) ppm; 13C NMR (400 MHz, CDCl3) 163.62 (30-CO),
d
1H NMR (400 MHz, CDCl3)
d
7.72 (d, J¼2.2 Hz, 1H, CH-arom.),
161.56 (20-CO), 149.37, 147.34, 144.87, 139.87, 138.07, 132.79,
131.77, 131.51, 129.87, 127.86, 121.28, 121.34, 120.95, 118.94, 100.88,
82.48 (acetylenic-C), 81.47 (acetylenic-C), 66.79 (80a-C), 66.41
(spiro-C), 53.41 (30-CH3), 51.08 (20-CH3), 22.41 (60-CH3), 21.18 (80-
7.30–7.39 (m, 4H, CH-arom.), 7.26 (d, J¼0.88 Hz, 1H, CH-arom.), 6.98
(dd, J¼1.76, 1.98 Hz, 1H, 60-CH), 5.45–5.49 (m, 1H, 70-CH), 4.95 (t,
J¼2.2 Hz, 1H, 8a0-CH), 4.72 (dt, J¼9.60, 1.76 Hz, 80-CH), 4.02 (s, 2H,
acetylenic-H), 3.90 (s, 3H, 30-CH3), 3.42 (s, 3H, 20-CH3) ppm; 13C
CH3) ppm; IR (KBr):
n
¼3079 (C–H, arom.), 2932–2977 (C-H,
NMR (400 MHz, CDCl3)
d
162.67 (30-CO), 161.36 (20-CO), 149.70,
aliph.), 2182 (acetylenic bond), 1741 (30-C]O), 1691 (20-C]O),
1608 (C]N), 1537 (C]C), 1426, 1379, 1287, 1168, 1068, 945, 879,
762 cmꢁ1; MS-EI m/e (%) 462.16 [Mþ]. Elemental analysis for
C29H22N2O4: C, 75.31; H, 4.79; N, 6.06. Found %: C, 75.32; H, 4.78;
N, 6.07.
148.47, 142.61, 138.99, 138.94, 138.12, 133.87, 133.18, 129.27, 128.76,
125.23, 124.98, 124.14, 121.22, 120.87, 118.97, 104.93, 82.42 (acety-
lenic-C), 81.40 (acetylenic-C), 65.36 (80a-C), 63.39 (spiro-C), 53.45
(30-CH3), 51.37 (20-CH3) ppm; IR (KBr):
n
¼3107–3070 (C–H, arom.),
2832–2969 (C–H, aliph.), 2167 (acetylenic bond),1747 (30-C]O),
1697 (20-C]O), 1591 (C]N), 1440 (C]C), 1333, 1249, 1194, 1087,
957, 889, 773 cmꢁ1; MS-EI m/e (%) 434.13 [Mþ]. Elemental analysis
for C27H18N2O4: C, 74.64; H, 4.18; N, 6.45. Found %: C, 74.65; H, 4.17;
N, 6.45.
4.2.5. Dimethyl 2,7-bis((4-ethynylphenyl)ethynyl)-20,4a0-dimethyl-
4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 10e
1H NMR (400 MHz, CDCl3)
d
7.67 (d, J¼1.45 Hz, 1H, CH-arom.),
7.63 (d, J¼7.86 Hz, 4H, arom.), 7.60 (d, J¼8.13 Hz, 2H, CH-arom.),
7.51 (d, J¼7.86 Hz, 4H, arom.), 7.48 (dd, J¼1.55, 1.97 Hz, 1H, CH-
arom.), 7.42–7.50 (m, 2H, CH-arom.), 5.53 (d, J¼9.73 Hz, 1H, 70-CH),
5.10 (d, J¼9.71 Hz, 1H, 80-CH), 4.22 (s, 2H, acetylenic-H), 3.97 (s, 3H,
30-CH3), 3.32 (s, 3H, 20-CH3), 2.09 (s, 3H, 60-CH3), 1.57 (s, 3H,
4.2.2. Dimethyl 2,7-bis((4-ethynylphenyl)ethynyl)-4a0H-
spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 10b
1H NMR (400 MHz, CDCl3)
d
7.65 (d, J¼7.86 Hz, 4H, arom.), 7.54 (d,
J¼7.86 Hz, 4H, arom.), 7.31 (d, J¼2.2 Hz,1H, CH-arom.), 7.27–7.36 (m,
4H, CH-arom.), 6.97 (d, J¼0.88 Hz, 1H, CH-arom.), 7.77 (dd, J¼1.76,
1.98 Hz, 1H, 60-CH), 5.49–5.51 (m, 1H, 70-CH), 4.94 (t, J¼2.2 Hz, 1H,
8a0-CH), 4.74 (dt, J¼9.60, 1.76 Hz, 80-CH), 4.08 (s, 2H, acetylenic-H),
3.94 (s, 3H, 30-CH3), 3.44 (s, 3H, 20-CH3) ppm; 13C NMR (400 MHz,
80-CH3) ppm; 13C NMR (400 MHz, CDCl3) 163.96 (30-CO), 161.54
d
(20-CO), 149.39, 147.31, 144.88, 139.73, 138.64, 132.87, 131.74, 131.57,
129.81, 127.86, 121.35, 121.23, 120.87, 118.87, 100.80, 93.39 (acety-
lenic-C), 91.67 (acetylenic-C), 82.57 (acetylenic-C), 81.44 (acetyle-
nic-C), 66.87 (80a-C), 66.57 (spiro-C), 53.47 (30-CH3), 51.11 (20-CH3),
CDCl3)
d
162.63 (30-CO),161.34 (20-CO),149.74,148.47,142.64,138.97,
22.51 (60-CH3), 21.27 (80-CH3) ppm; IR (KBr):
n
¼3087 (C–H, arom.),
138.97, 138.13, 133.84, 133.18, 131.93, 129.28, 128.77, 125.20, 124.95,
124.10, 122.43, 121.27, 120.87, 118.95, 104.97, 93.39 (acetylenic-C),
91.67(acetylenic-C), 82.47(acetylenic-C), 81.45 (acetylenic-C), 65.32
(80a-C), 63.45 (spiro-C), 53.48 (30-CH3), 51.33 (20-CH3) ppm; IR (KBr):
2980 (C–H, aliph.), 2178 (acetylenic bond), 1743 (30-C]O), 1697 (20-
C]O), 1612 (C]N), 1537 (C]C), 1434, 1384, 1281, 1197, 1070, 941,
889, 760 cmꢁ1; MS-EI m/e (%) 662.22 [Mþ]. Elemental analysis for
C45H30N2O4: C, 81.55; H, 4.56; N, 4.23. Found %: C, 81.55; H, 4.55; N,
4.24.
n
¼3138–3062 (C–H, arom.), 2837–2978 (C-H, aliph.), 2158 (acety-
lenic bond), 1756 (30-C]O), 1685 (20-C]O), 1597 (C]N), 1449
(C]C), 1342, 1257, 1192, 1098, 952, 882, 773 cmꢁ1; MS-EI m/e (%)
634.19 [Mþ]. Elemental analysis for C43H26N2O4: C, 81.37; H, 4.13; N,
4.41. Found %: C, 81.36; H, 4.15; N, 4.42.
4.2.6. Dimethyl 2,7-bis((4-((4-ethynylphenyl)ethynyl)phenyl)-
ethynyl)-20,4a0-dimethyl-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-
b]pyridazine]-60,70-dicarboxylate 10f
1H NMR (400 MHz, CDCl3)
d
7.68 (d, J¼7.86 Hz, 4H, arom.), 7.63
4.2.3. Dimethyl 2,7-bis((4-((4-ethynylphenyl)ethynyl)phenyl)-
ethynyl)-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 10c
(d, J¼7.86 Hz, 4H, arom.), 7.59 (d, J¼7.86 Hz, 4H, arom.), 7.54
(d, J¼7.86 Hz, 4H, arom.), 7.68 (d, J¼1.45 Hz, 1H, CH-arom.), 7.56 (d,
J¼8.20 Hz, 2H, CH-arom.), 7.47–7.49 (dd, J¼1.55, 1.98 Hz, 1H, CH-
arom.), 7.42–7.46 (m, 2H, CH-arom.), 5.42 (d, J¼9.60 Hz, 1H, 70-CH),
5.08 (d, J¼9.71 Hz, 1H, 80-CH), 4.27 (s, 2H, acetylenic-H), 3.92 (s, 3H,
30-CH3), 3.37 (s, 3H, 20-CH3), 2.18 (s, 3H, 60-CH3), 1.67 (s, 3H,
1H NMR (400 MHz, CDCl3)
d
7.65 (d, J¼7.86 Hz, 4H, arom.), 7.57
(d, J¼7.86 Hz, 4H, arom.), 7.54 (d, J¼7.86 Hz, 4H, arom.), 7.51 (d,
J¼7.86 Hz, 4H, arom.), 7.35 (d, J¼2.2 Hz, 1H, CH-arom.), 7.32–7.38
(m, 4H, CH-arom.), 6.96 (d, J¼0.88 Hz, 1H, CH-arom.), 7.73 (dd,
J¼1.76, 1.97 Hz, 1H, 60CH), 5.50–5.52 (m, 1H, 70-CH), 4.92 (t,
J¼2.2 Hz, 1H, 8a0-CH), 4.74 (dt, J¼9.60,1.76 Hz, 80-CH), 4.05 (s, 2H,
acetylenic-H), 3.92 (s, 3H, 30-CH3), 3.44 (s, 3H, 20-CH3) ppm; 13C
80-CH3) ppm; 13C NMR (400 MHz, CDCl3)
d
163.76 (30-CO), 161.65
(20-CO), 149.27, 147.37, 144.80, 139.77, 138.61, 132.88, 131.84, 131.63,
129.79, 127.38, 121.30, 121.24, 120.90, 118.97, 100.80, 93.45 (acetyl-
enic-C), 91.85 (acetylenic-C), 82.50 (acetylenic-C), 81.47 (acetyl-
enic-C), 66.76 (80a-C), 66.67 (spiro-C), 53.43 (30-CH3), 51.17 (20-CH3),
NMR (400 MHz, CDCl3)
148.42, 142.61, 138.97, 138.93, 138.10, 133.84, 133.27, 131.81, 129.29,
d
162.61 (30-CO), 161.37 (20-CO), 149.78,
22.59 (60-CH3), 21.36 (80-CH3) ppm; IR (KBr):
n
¼3120 (C–H, arom.),

S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
1383
2963 (C–H, aliph.), 2199 (acetylenic bond), 1749 (30-C]O), 1692 (20-
C]O), 1604 (C]N), 1539 (C]C), 1434, 1381, 1287, 1210, 1077, 946,
887, 766 cmꢁ1; MS-EI m/e (%) 862.28 [Mþ]. Elemental analysis for
C61H38N2O4: C, 84.90; H, 4.44; N, 3.25. Found %: C, 84.91; H, 4.43; N,
3.25.
analysis for C65H50N2O4Si2: C, 79.72; H, 5.15; N, 2.86. Found %: C,
79.71; H, 5.14; N, 2.86.
4.2.10. Dimethyl 20,4a0-dimethyl-2,7-bis((trimethylsilyl)ethynyl)-
4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 12d
4.2.7. Dimethyl 2,7-bis((trimethylsilyl)ethynyl)-4a0H-
spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 12a
1H NMR (400 MHz, CDCl3)
d
7.64 (d, J¼1.45 Hz, 1H, CH-arom.),
7.64 (d, J¼8.13 Hz, 2H, CH-arom.), 7.54 (dd, J¼1.55, 1.98 Hz, 1H, CH-
arom.), 7.44–7.47 (m, 2H, CH-arom.), 5.52 (d, J¼9.73 Hz, 1H, 70-CH),
5.12 (d, J¼9.71 Hz, 1H, 80-CH), 3.78 (s, 3H, 30-CH3), 3.33 (s, 3H, 20-
CH3), 2.15 (s, 3H, 60-CH3), 1.42 (s, 3H, 80-CH3), 0.24 (s, 18H,
1H NMR (400 MHz, CDCl3)
d
7.40 (d, J¼2.2 Hz, 1H, CH-arom.),
7.21–7.28 (m, 4H, CH-arom.), 7.04 (d, J¼0.88 Hz, 1H, CH-arom.),
7.71 (dd, J¼1.76, 1.99 Hz, 1H, 60-CH), 5.37–5.39 (m, 1H, 70-CH),
4.93 (t, J¼2.2 Hz, 1H, 8a0-CH), 4.69 (dt, J¼9.60, 1.76 Hz, 80-CH),
3.92 (s, 3H, 30-CH3), 3.40 (s, 3H, 20-CH3), 0.28 (s, 18H,
Si(CH3)3) ppm; 13C NMR (400 MHz, CDCl3)
d
136.63 (30-CO), 161.66
(20-CO), 149.46, 147.37, 144.90, 139.96, 138.16, 132.79, 131.96, 131.51,
129.67, 127.67, 121.34, 121.95, 120.34, 118.85, 100.86, 82.42 (acet-
ylenic-C), 81.31 (acetylenic-C), 66.67 (80a-C), 66.67 (spiro-C), 53.67
(30-CH3), 51.19 (20-CH3), 22.46 (60-CH3), 21.23 (80-CH3), 13.12
Si(CH3)3) ppm; 13C NMR (400 MHz, CDCl3)
d
162.62 (30-CO),
161.45 (20-CO), 149.78, 148.44, 142.62, 139.08, 138.87, 138.01,
133.89, 133.22, 129.29, 128.67, 125.45, 124.92, 124.10, 121.27,
120.68, 118.99, 104.84, 80.10 (acetylenic-C), 79.38 (acetylenic-C),
64.34 (80a-C), 62.97 (spiro-C), 51.46 (30-CH3), 50.67 (20-CH3), 13.69
(Si(CH3)3) ppm; IR (KBr):
n
¼3087 (C–H, arom.), 2960–2989 (C–H,
aliph.), 2164 (acetylenic bond), 1743 (30-C]O), 1697 (20-C]O),
1613 (C]N), 1540 (C]C), 1427, 1380, 1267, 1189, 1076, 947, 873,
749 cmꢁ1; MS-EI m/e (%) 606.24 [Mþ]. Elemental analysis for
C35H38N2O4Si2: C, 69.27; H, 6.31; N, 4.62. Found %: C, 69.28; H,
6.32; N, 4.60.
(Si(CH3)3) ppm; IR (KBr):
n
¼3149–3023 (C–H, arom.), 2849–2984
(C–H, aliph.), 2146 (acetylenic bond), 1741 (30-C]O), 1694 (20-
C]O), 1591 (C]N), 1442 (C]C), 1367, 1234, 1187, 1072, 955, 893,
778 cmꢁ1; MS-EI m/e (%) 578.21 [Mþ]. Elemental analysis for
C33H34N2O4Si2: C, 68.48; H, 5.92; N, 4.84. Found %: C, 68.49; H,
5.93; N, 4.82.
4.2.11. Dimethyl 20,4a0-dimethyl-2,7-bis((4-((trimethylsilyl)-
ethynyl)phenyl)ethynyl)-4a0H-spiro[fluorene-9,50-pyrrolo-
[1,2-b]pyridazine]-60,70-dicarboxylate 10e
4.2.8. Dimethyl 2,7-bis((4-((trimethylsilyl)ethynyl)phenyl)ethynyl)-
4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 12b
1H NMR (400 MHz, CDCl3)
d
7.64 (d, J¼1.45 Hz, 1H, CH-arom.),
7.60 (d, J¼7.86 Hz, 4H, arom.), 7.56 (d, J¼8.13 Hz, 2H, CH-arom.),
7.57 (d, J¼7.86 Hz, 4H, arom.), 7.48 (dd, J¼1.55, 1.97 Hz, 1H, CH-
arom.), 7.41–7.53 (m, 2H, CH-arom.), 5.60 (d, J¼9.73 Hz, 1H, 70-
CH), 5.13 (d, J¼9.71 Hz, 1H, 80-CH), 3.82 (s, 3H, 30-CH3), 3.39 (s, 3H,
20-CH3), 2.03 (s, 3H, 60-CH3), 1.46 (s, 3H, 80-CH3), 0.24 (s, 18H,
1H NMR (400 MHz, CDCl3)
d
7.62 (d, J¼7.86 Hz, 4H, arom.), 7.57
(d, J¼7.86 Hz, 4H, arom.), 7.36 (d, J¼2.2 Hz, 1H, CH-arom.), 7.29–
7.34 (m, 4H, CH-arom.), 6.96 (d, J¼0.88 Hz, 1H, CH-arom.), 7.74 (dd,
J¼1.76, 1.96 Hz, 1H, 60-CH), 5.50–5.53 (m, 1H, 70-CH), 4.93 (t,
J¼2.2 Hz, 1H, 8a0-CH), 4.75 (dt, J¼9.60, 1.76 Hz, 80-CH), 3.88 (s, 3H,
30-CH3), 3.41 (s, 3H, 20-CH3), 0.26 (s, 18H, Si(CH3)3) ppm; 13C NMR
Si(CH3)3) ppm; 13C NMR (400 MHz, CDCl3)
d
163.69 (30-CO),
162.01 (20-CO), 149.46, 147.37, 144.76, 139.71, 138.64, 132.64,
131.25, 131.46, 129.97, 127.67, 121.37, 121.64, 120.97, 118.98, 100.23,
93.46 (acetylenic-C), 91.67 (acetylenic-C), 82.46 (acetylenic-C),
81.79 (acetylenic-C), 66.37 (80a-C), 66.48 (spiro-C), 53.37 (30-CH3),
51.46 (20-CH3), 22.79 (60-CH3), 21.38 (80-CH3), 13.36
(400 MHz, CDCl3)
d
162.72 (30-CO), 161.17 (20-CO), 149.76, 148.44,
142.73, 138.81, 138.67, 138.22, 133.87, 133.27, 131.96, 129.36, 128.82,
125.36, 125.13, 124.64, 122.38, 121.21, 120.79, 118.76, 104.84, 93.32
(acetylenic-C), 90.99 (acetylenic-C), 81.67 (acetylenic-C), 80.44
(acetylenic-C), 64.79 (80a-C), 62.98 (spiro-C), 52.98 (30-CH3), 51.02
(Si(CH3)3) ppm; IR (KBr):
n
¼3081 (C–H, arom.), 2995 (C–H, aliph.),
2167 (acetylenic bond), 1740 (30-C]O), 1693 (20-C]O), 1613
(C]N), 1597 (C]C), 1433, 1394, 1287, 1182, 1046, 976, 879,
763 cmꢁ1; MS-EI m/e (%) 806.30 [Mþ]. Elemental analysis for
C51H46N2O4Si2: C, 75.90; H, 5.74; N, 3.47. Found %: C, 75.89; H,
5.73; N, 3.47.
(20-CH3), 13.97 (Si(CH3)3) ppm; IR (KBr):
n
¼3138–3095 (C–H,
arom.), 2867–2980 (C–H, aliph.), 2146 (acetylenic bond), 1754 (30-
C]O), 1687 (20-C]O), 1580 (C]N), 1457 (C]C), 1347, 1269, 1190,
1067, 957, 873, 795 cmꢁ1; MS-EI m/e (%) 778.27 [Mþ]. Elemental
analysis for C49H42N2O4Si2: C, 75.54; H, 5.43; N, 3.60. Found %: C,
75.53; H, 5.44; N, 3.60.
4.2.12. Dimethyl 20,4a0-dimethyl-2,7-bis((4-((4-((trimethylsilyl)-
ethynyl)phenyl)ethynyl)phenyl)ethynyl)-4a0H-spiro[fluorene-9,50-
pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 10f
4.2.9. Dimethyl 2,7-bis((4-((4-((trimethylsilyl)ethynyl)phenyl)-
ethynyl)phenyl)ethynyl)-4a0H-spiro[fluorene-9,50-pyrrolo-
[1,2-b]pyridazine]-60,70-dicarboxylate 12c
1H NMR (400 MHz, CDCl3)
d
7.80 (d, J¼7.86 Hz, 4H, arom.), 7.72
(d, J¼7.86 Hz, 4H, arom.), 7.64 (d, J¼7.86 Hz, 4H, arom.), 7.57 (d,
J¼7.86 Hz, 4H, arom.), 7.52 (d, J¼1.45 Hz, 1H, CH-arom.), 7.48 (d,
J¼8.20 Hz, 2H, CH-arom.), 7.45 (dd, J¼1.55, 1.98 Hz, 1H, CH-arom.),
7.40–7.42 (m, 2H, CH-arom.), 5.52 (d, J¼9.60 Hz, 1H, 70-CH), 5.26 (d,
J¼9.71 Hz, 1H, 80-CH), 3.85 (s, 3H, 30-CH3), 3.32 (s, 3H, 20-CH3), 2.23
(s, 3H, 60-CH3), 1.72 (s, 3H, 80-CH3), 0.28 (s, 18H, Si(CH3)3) ppm; 13C
1H NMR (400 MHz, CDCl3)
d
7.62 (d, J¼7.86 Hz, 4H, arom.), 7.52
(d, J¼7.86 Hz, 4H, arom.), 7.58 (d, J¼7.86 Hz, 4H, arom.), 7.56 (d,
J¼7.86 Hz, 4H, arom.), 7.35 (d, J¼2.2 Hz, 1H, CH-arom.), 7.36–7.39
(m, 4H, CH-arom.), 6.93 (d, J¼0.88 Hz, 1H, CH-arom.), 7.73 (dd,
J¼1.76, 1.98 Hz, 1H, 60-CH), 5.53–5.54 (m, 1H, 70-CH), 4.92 (t,
J¼2.2 Hz, 1H, 8a0-CH), 4.72 (dt, J¼9.60, 1.76 Hz, 80-CH), 3.86 (s, 3H,
30-CH3), 3.37 (s, 3H, 20-CH3), 0.24 (s, 18H, Si(CH3)3) ppm; 13C NMR
NMR (400 MHz, CDCl3)
d
163.81 (30-CO), 161.80 (20-CO), 149.36,
147.34, 144.79, 139.64, 138.57, 132.38, 131.57, 131.61, 129.37, 127.82,
121.64, 121.15, 120.60, 119.32, 100.67, 93.98 (acetylenic-C), 90.87
(acetylenic-C), 81.67 (acetylenic-C), 80.96 (acetylenic-C), 67.34 (80a-
C), 66.47 (spiro-C), 53.64 (30-CH3), 51.28 (20-CH3), 22.67 (60-CH3),
(400 MHz, CDCl3)
d
162.61 (30-CO), 162.43 (20-CO), 149.83, 148.47,
142.66, 138.82, 138.86, 138.37, 133.76, 133.10, 131.79, 129.64,
128.75, 125.37, 124.87, 124.13, 122.67, 121.36, 120.79, 118.87, 104.64,
93.36 (acetylenic-C), 90.67 (acetylenic-C), 81.79 (acetylenic-C),
80.39 (acetylenic-C), 65.46 (80a-C), 63.75 (spiro-C), 53.95 (30-CH3),
21.46 (80-CH3), 13.36 (Si(CH3)3) ppm; IR (KBr):
n
¼3099 (C–H,
arom.), 2895 (C–H, aliph.), 2184 (acetylenic bond), 1739 (30-C]O),
1697 (20-C]O), 1600 (C]N), 1549 (C]C), 1467, 1389, 1275, 1216,
1078, 969, 885, 767 cmꢁ1; MS-EI m/e (%) 1006.36 [Mþ]. Elemental
analysis for C67H54N2O4Si2: C, 79.89; H, 5.40; N, 2.78. Found %: C,
79.90; H, 5.41; N, 2.77.
51.64 (20-CH3), 13.97 (Si(CH3)3) ppm; IR (KBr):
n
¼3136–3079 (C–H,
arom.), 2837–2990 (C–H, aliph.), 2162 (acetylenic bond), 1750 (30-
C]O), 1687 (20-C]O), 1598 (C]N), 1474 (C]C), 1356, 1247, 1136,
1080, 957, 899, 774 cmꢁ1; MS-EI m/e (%) 978.33 [Mþ]. Elemental

1384
S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
4.3. Sonogashira-mediated coupling for the synthesis of
photochromic DHIs dimethyl 2,7-bis((4-(acetylthio)phenyl)-
ethynyl)n-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-
60,70-dicarboxylates 14a–f: general procedure
[Mþ]. Elemental analysis for C59H38N2O6S2: C, 75.78; H, 4.10; N, 3.00;
S, 6.86. Found %: C, 75.77; H, 4.11; N, 3.01; S, 6.86.
4.3.3. Dimethyl 2,7-bis((4-((4-((4-(acetylthio)phenyl)ethynyl)-
phenyl)ethynyl)phenyl)ethynyl)-4a0H-spiro[fluorene-9,50-
pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 14c
To an oven-dried screw cap tube or a round bottom flask
equipped with a water cooled condenser and a magnetic stir bar
were added 4-iodoacetyl-1-iodobenzene 13 (1.66 g, 6 mmol), bis
(dibenzylideneacetone)palladium(0) (172 mg, 0.3 mmol), copper(I)
iodide (114 mg, 0.6 mmol) and triphenylphosphine (314 mg,
0.12 mmol) to the terminal alkynes DHIs 12a–f (2.99 mmol). The
vessel was then sealed with a rubber septum, evacuated and
backfilled with nitrogen (3ꢀ). A co-solvent system of freshly dis-
tilled THF (40 mL) followed by DIEA (4.2 mL, 24 mmol) was added.
The reaction mixture was stirred in a 40 ꢂC oil bath for 3 h until the
reaction was complete. The reaction vessel was cooled to room
temperature and the mixture quenched with a saturated solution of
NH4Cl (20 mL). The organic layer was diluted with CH2Cl2 and
washed with a saturated solution of NH4Cl (3ꢀ20 mL). The com-
bined aqueous layers were extracted with CH2Cl2 (3ꢀ30 mL). The
combined organic layers were dried over anhydrous MgSO4 and the
solvent removed in vacuo. The crude products were then purified
by column chromatography on silica gel with CH2Cl2 as eluent. The
pure products were obtained as yellow needles. Full characteriza-
tions of the coupling products 14a–f are cited below:
1H NMR (400 MHz, CDCl3)
d
8.15 (d, J¼7.56 Hz, 4H, arom.),
8.07 (d, J¼7.86 Hz, 4H, arom.), 7.98 (d, J¼7.86 Hz, 4H, arom.),
7.74 (d, J¼7.86 Hz, 4H, arom.), 7.62 (d, J¼7.86 Hz, 4H, arom.),
7.47 (d, J¼7.86 Hz, 4H, arom.), 7.41 (d, J¼2.2 Hz, 1H, CH-arom.),
7.28–7.34 (m, 4H, CH-arom.), 7.17 (d, J¼1.00 Hz, 1H, CH-arom.),
7.11 (dd, J¼1.76, 1.86 Hz, 1H, 60-CH), 5.43–5.45 (m, 1H, 70-CH),
4.97 (t, J¼2.2 Hz, 1H, 8a0-CH), 4.71 (dt, J¼9.60, 1.76 Hz, 80-CH),
3.88 (s, 3H, 30-CH3), 3.36 (s, 3H, 20-CH3), 2.38 (s, 6H, 2CO-
CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 191.28 (CO–CH3),
163.14 (30-CO), 162.49 (20-CO), 152.27, 151.31, 149.36, 148.89,
142.73, 138.46, 138.87, 138.36, 133.75, 133.10, 131.54, 129.48,
128.36, 125.17, 124.80, 124.19, 122.97, 121.16, 120.84, 118.67,
104.90, 94.77 (acetylenic-C), 93.60 (acetylenic-C), 84.68 (acet-
ylenic-C), 82.36 (acetylenic-C), 64.79 (80a-C), 62.99 (spiro-C),
52.46 (30-CH3), 50.99 (20-CH3), 31.99 (CO-CH3) ppm; IR (KBr):
n
¼3099–3110 (C–H, arom.), 2849–2936 (C–H, aliph.), 2209
(acetylenic bond), 1746 (30-C]O), 1704 (CO–CH3), 1692 (20-
C]O), 1603 (C]N), 1469 (C]C), 1352, 1263, 1181, 1136, 957,
880, 759 cmꢁ1; MS-EI m/e (%) 1134.28 [Mþ]. Elemental analysis
for C75H46N2O6S2: C, 79.34; H, 4.08; N, 2.47; S, 5.65. Found %: C,
79.34; H, 4.10; N, 2.48; S, 5.64.
4.3.1. Dimethyl 2,7-bis((4-(acetylthio)phenyl)ethynyl)-4a0H-
spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 14a
4.3.4. Dimethyl 2,7-bis((4-(acetylthio)phenyl)ethynyl)-20,4a0-
dimethyl-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 14d
1H NMR (400 MHz, CDCl3)
d
8.13–815 (d, J¼1.6 Hz, 4H, arom.),
8.09 (d, J¼8.1 Hz, 4H, arom.), 7.92–7.94 (d, J¼2.2 Hz, 1H, CH-arom.),
7.76–7.82 (m, 4H, CH-arom.), 7.77 (dd, J¼1.76, 1.98 Hz, 1H, 60-CH),
7.14–7.16 (d, J¼0.88 Hz, 1H, CH-arom.), 5.53–5.57 (m, 1H, 70-CH),
4.83–4.86 (t, J¼2.2 Hz, 1H, 8a0-CH), 4.70–4.73 (dt, J¼9.60, 1.76 Hz,
80-CH), 3.86 (s, 3H, 30-CH3), 3.31 (s, 3H, 20-CH3), 2.43 (s, 6H, 2CO–
1H NMR (400 MHz, CDCl3)
d
8.25 (d, J¼1.6 Hz, 4H, arom.), 8.13
(d, J¼8.1 Hz, 4H, arom.), 8.03 (d, J¼1.45 Hz, 1H, CH-arom.), 7.59
(d, J¼8.13 Hz, 2H, CH-arom.), 7.43 (dd, J¼1.55, 1.96 Hz, 1H, CH-
arom.), 7.44–7.49 (m, 2H, CH-arom.), 5.60 (d, J¼9.56 Hz, 1H, 70-
CH), 5.00 (d, J¼9.71 Hz, 1H, 80-CH), 3.82 (s, 3H, 30-CH3), 3.47 (s,
3H, 20-CH3), 2.30 (CO–CH3), 2.10 (s, 3H, 60-CH3), 1.49 (s, 3H, 80-
CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 189.15 (CO–CH3), 163.75
(30-CO), 162.69 (20-CO), 150.20, 149.67, 148.21, 142.98, 138.97,
138.35, 138.13, 133.64, 133.38, 131.10, 129.41, 128.78, 125.78, 125.84,
124.58, 122.34, 121.38, 120.78, 118.36, 104.87, 98.26 (acetylenic-C),
96.47 (acetylenic-C), 65.37 (80a-C), 63.22 (spiro-C), 53.98 (30-CH3),
CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 190.12 (CO–CH3), 163.62
(30-CO), 162.20 (20-CO), 151.36, 149.69, 147.34, 144.95, 139.69,
138.13, 133.67, 131.97, 131.64, 129.78, 127.30, 121.48, 121.67,
120.92, 118.73, 101.36, 83.00 (acetylenic-C), 80.97 (acetylenic-C),
66.65 (80a-C), 66.32 (spiro-C), 53.12 (30-CH3), 51.57 (20-CH3),
31.82 (CO–CH3), 22.43 (60-CH3), 21.18 (80-CH3) ppm; IR (KBr):
51.00 (20-CH3), 30.84 (CO–CH3) ppm; IR (KBr):
n
¼3010–3098 (C–H,
arom.), 2898–2987 (C–H, aliph.), 2207 (acetylenic bond), 1756 (30-
C]O), 1709 (CO–CH3), 1695 (20-C]O), 1586 (C]N), 1454 (C]C),
1347, 1263, 1187, 1102, 958, 887, 776 cmꢁ1; MS-EI m/e (%) 734.15
[Mþ]. Elemental analysis for C43H30N2O6S2: C, 70.28; H, 4.11; N,
3.81; S, 8.73. Found %: C, 70.28; H, 4.10; N, 3.82; S, 8.75.
n
¼3022–3098 (C–H, arom.), 2912–2945 (C–H, aliph.), 2209
(acetylenic bond), 1745 (30-C]O), 1706 (CO–CH3), 1694 (20-
C]O), 1619 (C]N), 1535 (C]C), 1423, 1377, 1283, 1170, 1078,
939, 876, 765 cmꢁ1; MS-EI m/e (%) 762.19 [Mþ]. Elemental
analysis for C45H34N2O6S2: C, 70.85; H, 4.49; N, 3.67; S, 8.41.
Found %: C, 70.86; H, 4.48; N, 3.68; S, 8.42.
4.3.2. Dimethyl 2,7-bis((4-((4-(acetylthio)phenyl)ethynyl)-
phenyl)ethynyl)-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]-
pyridazine]-60,70-dicarboxylate 14b
1H NMR (400 MHz, CDCl3)
d
8.45 (d, J¼7.86 Hz, 4H, arom.), 8.30
4.3.5. Dimethyl 2,7-bis((4-((4-(acetylthio)phenyl)ethynyl)-
phenyl)ethynyl)-20,4a0-dimethyl-4a0H-spiro[fluorene-9,50-
pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 14e
(d, J¼7.86 Hz, 4H, arom.), 8.11 (d, J¼7.86 Hz, 4H, arom.), 7.83 (d,
J¼7.86 Hz, 4H, arom.), 7.71 (d, J¼2.2 Hz,1H, CH-arom.), 7.38–7.45 (m,
4H, CH-arom.), 7.92 (d, J¼0.88 Hz, 1H, CH-arom.), 7.60 (dd, J¼1.76,
1.99 Hz, 1H, 60-CH), 5.50–5.53 (m, 1H, 70-CH), 4.86 (t, J¼2.2 Hz, 1H,
8a0-CH), 4.77 (dt, J¼9.60,1.76 Hz, 80-CH), 3.94 (s, 3H, 30-CH3), 3.44 (s,
3H, 20-CH3), 2.39 (s, 6H, 2CO–CH3) ppm; 13C NMR (400 MHz, CDCl3)
1H NMR (400 MHz, CDCl3)
d
8.40 (d, J¼7.86 Hz, 4H, arom.),
8.40 (d, J¼7.86 Hz, 4H, arom.), 8.33 (d, J¼7.86 Hz, 4H, arom.),
7.93 (d, J¼7.86 Hz, 4H, arom.), 7.70 (d, J¼2.2 Hz, 1H, CH-arom.),
7.36–7.39 (m, 4H, CH-arom.), 7.91 (d, J¼0.88 Hz, 1H, CH-arom.),
7.68 (dd, J¼1.76, 1.96 Hz, 1H, 60-CH), 5.59–5.60 (m, 1H, 70-CH),
4.38 (dt, J¼9.60, 1.76 Hz, 80-CH), 3.90 (s, 3H, 30-CH3), 3.39 (s, 3H,
20-CH3), 2.32 (s, 6H, 2CO–CH3), 2.18 (s, 3H, 60-CH3), 1.43 (s, 3H,
d
191.87 (CO–CH3), 164.13 (30-CO), 162.64 (20-CO), 150.23, 149.22,
148.97, 142.14, 138.78, 138.36, 138.20, 133.79, 133.36, 131.84, 129.20,
128.81, 125.36, 124.87, 124.16, 122.98, 121.64, 120.93, 118.76, 104.82,
96.43 (acetylenic-C), 94.61 (acetylenic-C), 83.36 (acetylenic-C),
80.99 (acetylenic-C), 65.79 (80a-C), 63.42 (spiro-C), 53.63 (30-CH3),
80-CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 190.36 (CO–CH3),
163.28 (30-CO), 161.99 (20-CO), 151.26, 150.68, 149.32, 143.26,
139.36, 138.52, 138.33, 134.79, 133.67, 131.87, 129.39, 128.75,
125.47, 124.78, 124.13, 122.49, 120.96, 120.34, 118.60, 104.79,
96.34 (acetylenic-C), 93.98 (acetylenic-C), 82.36 (acetylenic-C),
80.32 (acetylenic-C), 65.46 (80a-C), 63.98 (spiro-C), 53.74
51.78 (20-CH3), 30.62 (CO-CH3) ppm; IR (KBr):
n
¼3089–3100 (C–H,
arom.), 2887–2989 (C–H, aliph.), 2236 (acetylenic bond), 1743 (30-
C]O), 1706 (CO–CH3), 1692 (20-C]O), 1582 (C]N), 1457 (C]C),
1357, 1264, 1190, 1112, 963, 876, 736 cmꢁ1; MS-EI m/e (%) 934.22

S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
1385
(30-CH3), 51.47 (20-CH3), 30.27 (CO–CH3), 22.41 (60-CH3), 21.23
(80-CH3) ppm; IR (KBr):
(C–H, aliph.), 2205 (acetylenic bond), 1741 (30-C]O), 1709
(CO–CH3), 1689 (20-C]O), 1578 (C]N), 1454 (C]C), 1336, 1274,
1182, 1116, 967, 874, 738 cmꢁ1; MS-EI m/e (%) 962.25 [Mþ].
Elemental analysis for C61H42N2O6S2: C, 76.07; H, 4.40; N, 2.91;
S, 6.66. Found %: C, 76.07; H, 4.41; N, 2.92; S, 6.87.
J¼1.20 Hz,1H, CH-arom.), 5.62–5.64 (m,1H, 70-CH), 4.83 (t, J¼2.2 Hz,
1H, 8a0-CH), 4.79 (dt, J¼9.60, 1.76 Hz, 80-CH), 4.13 (s, 1H, acetylenic-
H), 3.76 (s, 3H, 30-CH3), 3.38 (s, 3H, 20-CH3), 2.32 (s, 3H, CO-
n
¼3009–3098 (C–H, arom.), 2890–2974
CH3) ppm; 13C NMR (400 MHz, CDCl3) 190.06 (CO–CH3),163.77(30-
d
CO), 162.67 (20-CO), 149.66, 149.98, 142.62, 138.93, 138.79, 138.36,
133.79, 133.38, 131.36,129.98, 128.20, 125.75, 125.83, 124.46,122.67,
121.64, 120.82, 118.64, 104.36, 97.60 (acetylenic-C), 95.98 (acetyle-
nic-C), 81.85 (acetylenic-CH), 65.37 (80a-C), 63.84 (spiro-C), 53.63
4.3.6. Dimethyl 2-((4-((4-((4-(acetylthio)phenyl)ethynyl)-
phenyl)ethynyl)phenyl)ethynyl)-7-((4-((4-((4-(acetylthiomethyl)-
phenyl)ethynyl)phenyl)ethynyl)phenyl)ethynyl)-20,4a0-dimethyl-
4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 14f
(30-CH3), 50.67 (20-CH3), 30.31 (CO–CH3) ppm; IR (KBr):
n
¼3005–
3034 (C–H, arom.), 2860–2957 (C–H, aliph.), 2236 (acetylenic bond),
1749 (30-C]O), 1703 (CO–CH3), 1687 (20-C]O), 1588 (C]N), 1446
(C]C), 1339, 1267, 1172, 1163, 957, 886, 778 cmꢁ1; MS-EI m/e (%)
584.14 [Mþ]. Elemental analysis for C35H24N2O5S: C, 71.90; H, 4.14; N,
4.79; S, 5.48. Found %: C, 71.89; H, 4.13; N, 4.80; S, 5.47.
1H NMR (400 MHz, CDCl3)
d
8.22 (d, J¼7.56 Hz, 4H, arom.), 8.14
(d, J¼7.86 Hz, 4H, arom.), 7.99 (d, J¼7.86 Hz, 4H, arom.), 7.74 (d,
J¼7.86 Hz, 4H, arom.), 7.58 (d, J¼7.86 Hz, 4H, arom.), 7.48 (d,
J¼7.86 Hz, 4H, arom.), 7.47 (d, J¼2.2 Hz,1H, CH-arom.), 7.30–7.37 (m,
4H, CH-arom.), 7.20 (d, J¼1.00 Hz, 1H, CH-arom.), 5.44–5.46 (m, 1H,
70-CH), 4.73 (dt, J¼9.60, 1.76 Hz, 80-CH), 3.73 (s, 3H, 30-CH3), 3.42 (s,
3H, 20-CH3), 2.39 (s, 6H, 2CO–CH3), 2.14 (s, 3H, 60-CH3),1.46 (s, 3H, 80-
4.4.2. Dimethyl 2-((4-((4-(acetylthio)phenyl)ethynyl)phenyl)-
ethynyl)-7-((4-ethynylphenyl)ethynyl)-4a0H-spiro[fluorene-9,50-
pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 16b
1H NMR (400 MHz, CDCl3)
d
8.27 (d, J¼7.56 Hz, 2H, arom.), 8.02
(d, J¼7.86 Hz, 2H, arom.), 7.97 (d, J¼8.15 Hz, 2H, arom.), 7.78 (d,
J¼8.15 Hz, 2H, arom.), 7.45 (d, J¼7.86 Hz, 4H, arom.), 7.32 (d,
J¼7.86 Hz, 4H, arom.), 7.24 (d, J¼2.2 Hz, 1H, CH-arom.), 7.18–7.21
(m, 4H, CH-arom.), 7.13 (d, J¼1.25, 1.89 Hz, 1H, CH-arom.), 7.07 (dd,
J¼1.76, 1.97 Hz, 1H, 60-CH), 5.36–5.42 (m, 1H, 70-CH), 4.93 (t,
J¼2.2 Hz, 1H, 8a0-CH), 4.72 (dt, J¼8.25, 1.76 Hz, 80-CH), 4.12 (s, 1H,
acetylenic-H), 3.95 (s, 3H, 30-CH3), 3.43 (s, 3H, 20-CH3), 2.20 (s, 3H,
CH3) ppm; 13C NMR (400 MHz, CDCl3) 191.27 (CO–CH3),163.17 (30-
d
CO), 162.46 (20-CO), 152.36, 151.49, 149.22, 148.79, 142.64, 138.34,
138.79, 138.38, 133.67, 133.15, 131.56, 129.50, 128.46, 125.76, 124.34,
124.18, 122.76, 121.36, 120.49, 118.75, 104.61, 94.78 (acetylenic-C),
93.79 (acetylenic-C), 84.36 (acetylenic-C), 82.47 (acetylenic-C),
64.87 (80a-C), 62.94 (spiro-C), 52.41 (30-CH3), 50.48 (20-CH3), 31.36
(CO–CH3), 22.47 (60-CH3), 21.34 (80-CH3) ppm; IR (KBr):
n¼3000–
CO–CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 190.98 (CO–CH3),
3095 (C–H, arom.), 2898–2964 (C–H, aliph.), 2201 (acetylenic bond),
1741 (30-C]O), 1707 (CO–CH3), 1689 (20-C]O), 1610 (C]N), 1461
(C]C), 1355, 1267, 1183, 1140, 960, 884, 787 cmꢁ1; MS-EI m/e (%)
1176.33 [Mþ]. Elemental analysis for C78H52N2O6S2: C, 79.57; H, 4.45;
N, 2.38; S, 5.45. Found %: C, 79.56; H, 4.46; N, 2.37; S, 5.47.
162.25 (30-CO),161.52 (20-CO),150.28,149.30,148.97,142.85,138.52,
138.49, 138.73, 132.20, 131.95, 131.03, 129.27, 128.69, 125.27, 124.87,
124.36, 121.38, 120.67, 120.31, 119.97, 105.91, 94.85 (acetylenic-C),
92.99 (acetylenic-C), 85.67 (acetylenic-C), 82.03 (acetylenic-C),
64.67 (80a-C), 62.62 (spiro-C), 52.74 (30-CH3), 51.23 (20-CH3), 32.06
(CO-CH3) ppm; IR (KBr):
n
¼3016–3100 (C–H, arom.), 2910–2978
4.4. Sonogashira-mediated coupling for the synthesis of
photochromic DHIs (50S)-dimethyl 2-((4-(acetylthio)phenyl)-
ethynyl)n-7-ethynyl-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-
b]pyridazine]-60,70-dicarboxylates 16a–f: general procedure
(C–H, aliph.), 2211 (acetylenic bond), 1741 (30-C]O), 1700 (CO–
CH3), 1689 (20-C]O), 1600 (C]N), 1475 (C]C), 1349, 1253, 1173,
1138, 965, 878, 746 cmꢁ1; MS-EI m/e (%) 784.20 [Mþ]. Elemental
analysis for C51H32N2O5S: C, 78.04; H, 4.11; N, 3.57; S, 4.09. Found %:
C, 78.04; H, 4.10; N, 3.58; S, 4.08.
To an oven-dried screw cap tube or a round bottom flask
equipped with a water cooled west condenser and a magnetic stir
bar were added 4-iodoacetyl-1-iodobenzene 1347 (0.831 g,
2.99 mmol), bis(dibenzylideneacetone)palladium(0) (0.086 mg,
0.149 mmol), copper(I) iodide (0.057 mg, 0.30 mmol) and triphe-
nylphosphine (0.157 mg, 0.060 mmol) to the terminal alkynes DHIs
12a–f (2.99 mmol). The vessel was then sealed with a rubber sep-
tum, evacuated and backfilled with nitrogen (3ꢀ). A co-solvent
system of freshly distilled THF (20 mL) followed by DIEA (2.1 mL,
12 mmol) was added. The reaction mixture was stirred in a 40 ꢂC oil
bath for 3 h (TLC controlled) until the reaction was complete. The
reaction vessel was cooled to room temperature and the mixture
quenched with water or a saturated solution of NH4Cl. The organic
layer was diluted with CH2Cl2 and washed with a saturated solution
of NH4Cl (3ꢀ30 mL). The combined aqueous layers were extracted
with CH2Cl2 (3ꢀ30 mL). The combined organic layers were dried
over anhydrous MgSO4 and the solvent removed in vacuo. The
crude products were then purified twice by column chromatogra-
phy on silica gel and CH2Cl2 as eluent. The pure products were
obtained in high purity as yellow needles. Full characterizations of
the coupling products 16a–f are cited below:
4.4.3. Dimethyl 2,7-bis((4-((4-((4-(acetylthio)-
phenyl)ethynyl)phenyl)ethynyl)phenyl)ethynyl)-4a0H-spiro-
[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 16c
1H NMR (400 MHz, CDCl3)
d 8.32–8.40 (m, 8H, arom.), 8.21–8.24
(m, 4H, arom.), 8.11 (d, J¼1.6 Hz, 4H, arom.), 8.09 (d, J¼8.1 Hz, 4H,
arom.), 8.04 (d, J¼1.45 Hz,1H, CH-arom.), 7.63 (d, J¼8.16 Hz, 2H, CH-
arom.), 7.42 (dd, J¼1.55, 1.98 Hz, 1H, CH-arom.), 7.41–7.42 (m, 2H,
CH-arom.), 5.63 (d, J¼9.56 Hz, 1H, 70-CH), 5.09 (d, J¼9.71 Hz, 1H,
80-CH), 5.06 (s, 1H, acetylenic-H), 3.80 (s, 3H, 30-CH3), 3.41 (s, 3H,
20-CH3), 2.29 (CO–CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 191.90
(CO–CH3), 163.02 (30-CO), 162.98 (20-CO), 150.39, 149.46, 148.76,
142.34, 138.74, 138.30, 138.78, 131.13, 130.97, 130.28, 130.89, 128.64,
125.27, 124.87, 124.70, 120.69, 120.30, 120.01, 119.35, 106.39, 93.99
(acetylenic-C), 91.76 (acetylenic-C), 82.63 (acetylenic-C), 81.98
(acetylenic-C), 63.70 (80a-C), 63.09 (spiro-C), 51.71 (30-CH3), 51.69
(20-CH3), 32.16 (CO–CH3) ppm; IR (KBr):
n
¼3004–3098 (C–H,
arom.), 2923–2985 (C–H, aliph.), 2207 (acetylenic bond), 1747 (30-
C]O), 1706 (CO–CH3), 1695 (20-C]O), 1607 (C]N), 1463 (C]C),
1363, 1243, 1160, 1178, 979, 864, 741 cmꢁ1; MS-EI m/e (%) 984.27
[Mþ]. Elemental analysis for C67H40N2O5S: C, 81.69; H, 4.09; N, 2.84;
S, 3.25. Found %: C, 81.70; H, 4.08; N, 2.84; S, 3.24.
4.4.1. Dimethyl 2-((4-(acetylthio)phenyl)ethynyl)-7-ethynyl-4a0H-
spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 16a
4.4.4. Dimethyl 2-((4-(acetylthio)phenyl)ethynyl)-7-ethynyl-20,4a0-
dimethyl-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylate 16d
1H NMR (400 MHz, CDCl3)
d
8.27 (d, J¼1.6 Hz, 2H, arom.), 8.13 (d,
J¼8.1 Hz, 2H, arom.), 7.87 (d, J¼2.2 Hz, 1H, CH-arom.), 7.74–7.78 (m,
1H NMR (400 MHz, CDCl3)
(d, J¼8.1 Hz, 2H, arom.), 8.02 (d, J¼1.65 Hz, 1H, CH-arom.), 7.87 (d,
d
8.17 (d, J¼1.6 Hz, 2H, arom.), 8.07
4H, CH-arom.), 7.77 (dd, J¼1.76, 1.89 Hz, 1H, 60-CH), 7.17 (d,

1386
S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
J¼8.13 Hz, 2H, CH-arom.), 7.54 (dd, J¼1.60, 1.99 Hz, 1H, CH-arom.),
7.49–7.52 (m, 2H, CH-arom.), 5.66 (d, J¼9.56 Hz, 1H, 70-CH), 5.28
(d, J¼9.71 Hz, 1H, 80-CH), 4.01 (s, 1H, acetylenic-H), 3.79 (s, 3H, 30-
CH3), 3.36 (s, 3H, 20-CH3), 2.24 (CO–CH3), 2.16 (s, 3H, 60-CH3), 1.34
4.4.7. Sonogashira-mediated coupling for the synthesis of
photochromic DHIs dimethyl 2,7-bis((4-(acetylthio)phenyl)-
ethynyl)n-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylates 18a–f
These compounds prepared by following the general procedure
mentioned for 16a–f. The pure products were obtained with highly
purity as yellow needles. Full characterizations of the coupling
products 18a–f are cited below:
(s, 3H, 80-CH3) ppm; 13C NMR (400 MHz, CDCl3)
d
191.32 (CO–
CH3), 162.98 (30-CO), 161.67 (20-CO), 150.17, 149.37, 147.30, 145.02,
139.37, 139.03, 134.21, 132.00, 131.69, 129.76, 127.57, 121.62,
121.78, 120.31, 118.85, 101.84, 85.61 (acetylenic-C), 84.37 (acetyl-
enic-C), 83.61 (acetylenic-C), 80.20 (acetylenic-C), 66.21 (80a-C),
65.69 (spiro-C), 52.99 (30-CH3), 50.60 (20-CH3), 31.49 (CO–CH3),
4.4.8. Dimethyl 2-((4-(acetylthio)phenyl)ethynyl)-7-
(phenylethynyl)-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]-
pyridazine]-60,70-dicarboxylate 18a
22.27 (60-CH3), 20.98 (80-CH3) ppm; IR (KBr):
n
¼3009–3078 (C–H,
arom.), 2896–2978 (C–H, aliph.), 2214 (acetylenic bond), 1742 (30-
C]O), 1701 (CO–CH3), 1685 (20-C]O), 1607 (C]N), 1534 (C]C),
1436, 1349, 1237, 1174, 1101, 946, 868, 766 cmꢁ1; MS-EI m/e (%)
612.17 [Mþ]. Elemental analysis for C37H28N2O5S: C, 72.53;
H, 4.61; N, 4.57; S, 5.23. Found %: C, 72.52; H, 4.62; N, 4.55; S,
5.22.
1H NMR (400 MHz, CDCl3)
d
8.23 (d, J¼1.6 Hz, 4H, arom.), 8.13 (d,
J¼8.1 Hz, 4H, arom.), 8.03 (t, J¼5.6 Hz, 1H, CH-arom.), 7.96 (d,
J¼2.2 Hz, 1H, CH-arom.), 7.72–7.78 (m, 4H, CH-arom.), 7.74
(dd, J¼1.76, 2.01 Hz, 1H, 60-CH), 7.24 (d, J¼0.88 Hz, 1H, CH-arom.),
5.61 (m, 1H, 70-CH), 4.90 (t, J¼2.2 Hz, 1H, 8a0-CH), 4.74 (dt, J¼9.60,
1.76 Hz, 80-CH), 3.80 (s, 3H, 30-CH3), 3.33 (s, 3H, 20-CH3), 2.40 (s, 3H,
4.4.5. Dimethyl 2-((4-((4-(acetylthio)phenyl)ethynyl)phenyl)-
ethynyl)-7-((4-ethynylphenyl)ethynyl)-20,4a0-dimethyl-4a0H-spiro-
[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 16e
CO-CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 190.03 (CO–CH3),
162.74 (30-CO), 161.99 (20-CO), 150.26, 150.13, 149.46, 142.33, 138.57,
138.96, 138.22, 133.46, 133.78, 131.36, 129.67, 128.36, 125.46, 125.58,
125.23, 124.36, 122.67, 120.69, 118.34, 104.78, 98.62 (acetylenic-C),
95.56 (acetylenic-C), 65.36 (80a-C), 62.99 (spiro-C), 54.21 (30-CH3),
1H NMR (400 MHz, CDCl3)
d
8.31 (d, J¼7.56 Hz, 2H, arom.), 8.25
(d, J¼7.86 Hz, 2H, arom.), 8.20 (d, J¼7.86 Hz, 4H, arom.), 7.86 (d,
J¼7.86 Hz, 4H, arom.), 7.78 (d, J¼2.2 Hz, 1H, CH-arom.), 7.49–7.57
(m, 4H, CH-arom.), 7.85 (d, J¼0.88 Hz, 1H, CH-arom.), 7.62 (dd,
J¼1.76, 1.88 Hz, 1H, 60-CH), 5.46–5.50 (m, 1H, 70-CH), 4.51 (dt,
J¼9.60, 1.76 Hz, 80-CH), 4.12 (s, 1H, acetylenic-H), 3.92 (s, 3H, 30-
CH3), 3.42 (s, 3H, 20-CH3), 2.28 (s, 3H, CO–CH3), 2.23 (s, 3H, 60-
52.32 (20-CH3), 31.54 (CO–CH3) ppm; IR (KBr):
n
¼3000–3102 (C–H,
arom.), 2862–2934 (C–H, aliph.), 2211 (acetylenic bond), 1751 (30-
C]O), 1701 (CO-CH3), 1694 (20-C]O), 1587 (C]N), 1464 (C]C),
1353, 1251, 1178, 1111, 957, 881, 784 cmꢁ1; MS-EI m/e (%) 660.17
[Mþ]. Elemental analysis for C41H28N2O5S: C, 74.53; H, 4.27; N, 4.24;
S, 4.85. Found %: C, 74.54; H, 4.27; N, 4.23; S, 8.83.
CH3), 1.39 (s, 3H, 80-CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 191.36
(CO–CH3), 162.89 (30-CO), 160.56 (20-CO), 150.78, 150.30, 149.54,
143.31, 139.68, 138.74, 138.69, 134.85, 133.36, 132.25, 130.67,
128.95, 125.34, 124.75, 124.36, 122.97, 118.48, 104.97, 95.37
(acetylenic-C), 93.21 (acetylenic-C), 82.45 (acetylenic-C), 80.85
(acetylenic-C), 65.30 (80a-C), 63.78 (spiro-C), 53.26 (30-CH3), 51.48
(20-CH3), 30.20 (CO–CH3), 22.42 (60-CH3), 21.36 (80-CH3) ppm; IR
4.4.9. Dimethyl 2-((4-((4-(acetylthio)phenyl)ethynyl)-
phenyl)ethynyl)-7-((4-(phenylethynyl)phenyl)ethynyl)-4a0H-spiro-
[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 18b
1H NMR (400 MHz, CDCl3)
d
8.34 (d, J¼7.60 Hz, 4H, arom.), 8.26
(d, J¼7.60 Hz, 4H, arom.), 8.15–8.18 (m, 5H, arom.), 7.94 (d, J¼7.86 Hz,
4H, arom.), 7.87 (d, J¼2.2 Hz, 1H, CH-arom.), 7.36–7.43 (m, 4H, CH-
arom.), 7.91 (d, J¼0.88 Hz, 1H, CH-arom.), 7.66 (dd, J¼1.60, 1.96 Hz,
1H, 60-CH), 5.51–5.54 (m, 1H, 70-CH), 4.84 (t, J¼2.2 Hz, 1H, 8a0-CH),
4.72 (dt, J¼9.60, 1.76 Hz, 80-CH), 3.90 (s, 3H, 30-CH3), 3.46 (s, 3H, 20-
(KBr):
n
¼3025–3110 (C–H, arom.), 2839–2945 (C–H, aliph.), 2213
(acetylenic bond), 1746 (30-C]O), 1712 (CO–CH3), 1680 (20-C]O),
1563 (C]N), 1450 (C]C), 1330, 1268, 1173, 1164, 956, 878,
730 cmꢁ1; MS-EI m/e (%) 812.23 [Mþ]. Elemental analysis for
C53H36N2O5S: C, 78.31; H, 4.46; N, 3.45; S, 3.94. Found %: C, 78.32;
H, 4.45; N, 3.44; S, 3.92.
CH3), 2.31 (s, 3H, CO–CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 191.82
(CO–CH3), 164.46 (30-CO), 162.20 (20-CO), 150.67, 150.00, 148.84,
142.36, 138.64, 139.22, 139.27, 133.36, 133.20, 131.40, 129.67, 128.81,
125.93, 124.78, 124.28, 123.00, 122.64, 121.93, 119.67, 104.52, 96.64
(acetylenic-C), 94.96 (acetylenic-C), 82.01 (acetylenic-C), 80.98
(acetylenic-C), 64.97 (80a-C), 63.35 (spiro-C), 53.85 (30-CH3), 50.99
4.4.6. Dimethyl 2-((4-((4-((4-(acetylthio)phenyl)ethynyl)phenyl)-
ethynyl)phenyl)ethynyl)-7-((4-((4-ethynylphenyl)ethynyl)-
phenyl)ethynyl)-20,4a0-dimethyl-4a0H-spiro[fluorene-9,50-
pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 16f
(20-CH3), 30.84 (CO–CH3) ppm; IR (KBr):
n
¼3036–3098 (C–H, arom.),
1H NMR (400 MHz, CDCl3)
d
8.25 (d, J¼7.60 Hz, 2H, arom.), 8.22
2868–2973 (C–H, aliph.), 2216 (acetylenic bond), 1740 (30-C]O),
1701 (CO–CH3),1663 (20-C]O),1585 (C]N),1464 (C]C),1358,1274,
1192, 1110, 967, 873, 735 cmꢁ1; MS-EI m/e (%) 860.23 [Mþ]. Ele-
mental analysis for C57H36N2O5S: C, 79.52; H, 4.21; N, 3.25; S, 3.72.
Found %: C, 79.52; H, 4.20; N, 3.24; S, 3.70.
(d, J¼7.60 Hz, 2H, arom.), 8.14 (d, J¼7.60 Hz, 4H, arom.), 8.10 (d,
J¼7.86 Hz, 4H, arom.), 7.97 (d, J¼7.86 Hz, 4H, arom.), 7.66 (d,
J¼7.86 Hz, 4H, arom.), 7.41 (d, J¼2.2 Hz, 1H, CH-arom.), 7.36–7.39
(m, 4H, CH-arom.), 7.25 (d, J¼1.15 Hz, 1H, CH-arom.), 5.42–5.49 (m,
1H, 70-CH), 4.69 (dt, J¼9.60, 1.76 Hz, 80-CH), 4.20 (s, 1H, acetylenic-
H), 3.69 (s, 3H, 30-CH3), 3.46 (s, 3H, 20-CH3), 2.40 (s, H, CO–CH3), 2.11
(s, 3H, 60-CH3), 1.37 (s, 3H, 80-CH3) ppm; 13C NMR (400 MHz, CDCl3)
4.4.10. Dimethyl 2-((4-((4-((4-(acetylthio)phenyl)ethynyl)-
phenyl)ethynyl)phenyl)ethynyl)-7-((4-((4-(phenylethynyl)phenyl)-
ethynyl)phenyl)ethynyl)-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-
b]pyridazine]-60,70-dicarboxylate 18c
d
191.46 (CO–CH3), 163.48 (30-CO), 162.69 (20-CO), 152.78, 151.62,
149.37, 148.21, 142.36, 138.78, 138.49, 138.15, 133.97, 133.25, 130.98,
130.48, 129.20, 125.32, 124.10, 124.48, 122.79, 121.54, 120.78, 119.63,
104.25, 94.74 (acetylenic-C), 92.82 (acetylenic-C), 83.46 (acetyle-
nic-C), 88.63 (acetylenic-C), 64.89 (80a-C), 63.87 (spiro-C), 52.32
(30-CH3), 50.46 (20-CH3), 30.89 (CO–CH3), 22.36 (60-CH3), 21.47 (80-
1H NMR (400 MHz, CDCl3)
d
8.20 (d, J¼7.56 Hz, 4H, arom.), 8.12 (d,
J¼7.86 Hz, 4H, arom.), 7.96–8.01 (m, 5H, arom.), 7.71 (d, J¼7.86 Hz,
4H, arom.), 7.54 (d, J¼7.86 Hz, 4H, arom.), 7.51 (d, J¼7.86 Hz, 4H,
arom.), 7.42 (d, J¼2.2 Hz, 1H, CH-arom.), 7.30–7.35 (m, 4H, CH-
arom.), 7.18 (d, J¼1.00 Hz,1H, CH-arom.), 7.13 (dd, J¼1.76,1.88 Hz,1H,
60-CH), 5.40–5.43 (m, 1H, 70-CH), 5.01 (t, J¼2.2 Hz, 1H, 8a0-CH), 4.76
(dt, J¼9.60, 1.76 Hz, 80-CH), 3.81 (s, 3H, 30-CH3), 3.35 (s, 3H, 20-CH3),
CH3) ppm; IR (KBr):
n
¼3024–3100 (C–H, arom.), 2869–2932 (C–H,
aliph.), 2219 (acetylenic bond), 1746 (30-C]O), 1702 (CO–CH3), 1690
(20-C]O),1615 (C]N),1465 (C]C),1354,1263,1185,1144, 967, 888,
786 cmꢁ1; MS-EI m/e (%) 1012.30 [Mþ]. Elemental analysis for
C69H44N2O5S: C, 81.80; H, 4.38; N, 2.76; S, 3.16. Found %: C, 81.81; H,
4.38; N, 2.77; S, 3.15.
2.32 (s, 3H, CO–CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 192.36 (CO–
CH3), 164.13 (30-CO), 161.99 (20-CO), 151.06, 150.78, 150.39, 148.64,
142.36, 138.78, 138.46, 138.12, 133.23, 133.15, 131.57, 129.79, 128.64,

S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
1387
125.01, 124.67, 124.57, 122.39, 121.78, 120.64, 118.82, 104.67, 94.32
(acetylenic-C), 92.98 (acetylenic-C), 83.87 (acetylenic-C), 82.20
(acetylenic-C), 64.67 (80a-C), 62.65 (spiro-C), 52.47 (30-CH3), 50.87
(30-CO),161.98 (20-CO),151.39,150.48,149.32,148.48,141.36,138.65,
138.36, 138.30, 133.28, 133.17, 131.39, 129.20, 128.78, 125.64, 124.38,
124.58, 122.37, 121.30, 120.85, 118.61, 104.74, 94.82 (acetylenic-C),
92.77 (acetylenic-C), 85.00 (acetylenic-C), 81.78 (acetylenic-C),
64.38 (80a-C), 62.84 (spiro-C), 52.48 (30-CH3), 50.74 (20-CH3), 31.61
(20-CH3), 31.23 (CO–CH3) ppm; IR (KBr):
n
¼3039–3100 (C–H, arom.),
2858–2997 (C–H, aliph.), 2202 (acetylenic bond), 1739 (30-C]O),
1701 (CO–CH3),1693 (20-C]O),1600 (C]N),1467 (C]C),1357,1245,
1178, 1196, 967, 886, 734 cmꢁ1; MS-EI m/e (%) 1060.30 [Mþ]. Ele-
mental analysis for C73H44N2O5S: C, 82.62; H, 4.18; N, 2.64; S, 3.02.
Found %: C, 82.63; H, 4.17; N, 2.64; S, 3.01.
(CO–CH3), 22.75 (60-CH3), 21.21 (80-CH3) ppm; IR (KBr):
n
¼3006–
3078 (C–H, arom.), 2886–2961 (C–H, aliph.), 2217 (acetylenic
bond), 1745 (30-C]O), 1701 (CO–CH3), 1686 (20-C]O), 1600 (C]N),
1468 (C]C), 1354, 1262, 1187, 1142, 961, 883, 772 cmꢁ1; MS-EI m/e
(%) 1088.33 [Mþ]. Elemental analysis for C75H48N2O5S: C, 82.70; H,
4.44; N, 2.57; S, 2.94. Found %: C, 82.71; H, 4.43; N, 2.57; S, 2.93.
4.4.11. Dimethyl 2-((4-(acetylthio)phenyl)ethynyl)-20,4a0-dimethyl-
7-(phenylethynyl)-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-
b]pyridazine]-60,70-dicarboxylate 18d
Acknowledgements
1H NMR (400 MHz, CDCl3)
d
8.45 (d, J¼1.6 Hz, 4H, arom.), 8.24
(d, J¼8.1 Hz, 4H, arom.), 8.12 (d, J¼1.45 Hz, 1H, CH-arom.), 7.59–7.62
(m, 3H, CH-arom.), 7.44 (dd, J¼1.55, 1.87 Hz, 1H, CH-arom.), 7.43–
7.47 (m, 2H, CH-arom.), 5.62 (d, J¼9.56 Hz, 1H, 70-CH), 5.11 (d,
J¼9.71 Hz, 1H, 80-CH), 3.80 (s, 3H, 30-CH3), 3.43 (s, 3H, 20-CH3), 2.33
(CO–CH3), 2.17 (s, 3H, 60-CH3), 1.52 (s, 3H, 80-CH3) ppm; 13C NMR
The author is highly indebted to Alexander von Humboldt
foundation for partially supporting this work. Many thanks to Prof.
Dr. Heinz Du¨rr (University of Saarland, Saarbru¨cken, Germany),
Prof. Dr. Henri Bouas-Laurent and Prof. Dr. Jean-Luc Pozzo for their
continuous helpful discussions and measurements. The financial
support from Alexander von Humboldt (AvH) and Taibah University
is gratefully acknowledged.
(400 MHz, CDCl3) d
191.13 (CO–CH3), 162.87 (30-CO), 161.99 (20-CO),
150.92, 149.39, 147.37, 144.85, 139.67, 138.37, 133.58, 131.27, 131.98,
129.47, 127.25, 121.53, 121.46, 120.87, 118.58, 101.36, 83.25 (acety-
lenic-C), 81.02 (acetylenic-C), 66.25 (80a-C), 66.43 (spiro-C), 52.12
(30-CH3), 51.53 (20-CH3), 31.85 (CO–CH3), 22.21 (60-CH3), 21.20 (80-
References and notes
1. (a) Bouas-Laurent, H.; Du¨rr, H. Pure Appl. Chem. 2001, 73, 639–665; (b) Irie, M. In
Molecular Switches; Feringa, B. L., Ed.; Wiley-VCH: Weinheim, 2001; pp 37–60.
2. Irie, M. In Organic Photochromic and Thermochromic Compounds; Crano, J. C.,
Gugielmetti, R. J., Eds.; Plenum: New York, NY, 1999; Vol. 1, pp 207–221.
3. Tian, H.; Chen, B.; Tu, H.; Mu¨llen, K. Adv. Mater. 2002, 14, 918–923.
4. Irie, M.; Fukaminato, T.; Sasaki, T.; Tamai, N.; Kawai, T. Nature 2002, 420, 759–760.
5. Norsten, T. B.; Branda, N. R. J. Am. Chem. Soc. 2001, 123, 1784–1785.
6. Norsten, T. B.; Branda, N. R. Adv. Mater. 2001, 13, 347–349.
CH3) ppm; IR (KBr):
n
¼3036–3058 (C–H, arom.), 2912–2958 (C–H,
aliph.), 2247 (acetylenic bond), 1746 (30-C]O), 1702 (CO–CH3), 1691
(20-C]O), 1620 (C]N), 1537 (C]C), 1426, 1378, 1286, 1178, 1075,
932, 871, 767 cmꢁ1; MS-EI m/e (%) 688.20 [Mþ]. Elemental analysis
for C43H32N2O5S: C, 74.98; H, 4.68; N, 4.07; S, 4.66. Found %: C,
74.98; H, 4.68; N, 4.07; S, 4.66.
7. Tsivgoulis, G.; Lehn, J.-M. Angew. Chem., Int. Ed. Engl. 1995, 34, 1119–1122.
8. Tsujioka, T.; Hamada, Y.; Shibata, K. Appl. Phys. Lett. 2001, 78, 2282–2284.
9. Kawai, T.; Kunitake, K.; Irie, M. Chem. Lett. 1999, 905–906.
4.4.12. Dimethyl 2-((4-((4-(acetylthio)phenyl)ethynyl)phenyl)-
ethynyl)-20,4a0-dimethyl-7-(phenylethynyl)-4a0H-spiro[fluorene-
9,50-pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 18e
10. Bertarelli, C.; Bianco, A.; D0 Amore, F.; Gallazzi, M. C.; Zerbi, G. Adv. Funct. Mater.
2004, 14, 357–363.
1H NMR (400 MHz, CDCl3)
d
8.38 (d, J¼7.86 Hz, 4H, arom.), 8.34
11. Kim, M. S.; Maruyama, H.; Kawat, T.; Irie, M. Chem. Mater. 2003, 15, 4539–4543.
12. Kim, E.; Choi, Y.-K.; Lee, M.-H. Macromolecules 1999, 32, 4855–4860.
13. Biteau, J.; Chaput, C.; Lahlil, K.; Boilot, J.-P.; Tsivgoulis, G. M.; Lehn, J.-M.; Dar-
racq, B.; Marois, C.; Le´vy, Y. Chem. Mater. 1998, 10, 1945–1950.
14. van Delden, R. A.; ter Wiel, M. K. J.; Feringa, B. L. Chem. Commun. 2004, 200–201.
15. Feringa, B. L.; van Delden, R. A.; ter Wiel, M. K. J. In Molecular Switches; Feringa,
B. L., Ed.; Wiley-VCH: Weinheim, 2001; pp 123–164.
16. Murguly, E.;Norsten, T. B.; Branda,N. R. Angew. Chem., Int. Ed. 2001, 40,1752–1755.
17. Moniruzzaman, M.; Sabey, C. G.; Fernando, G. F. Macromolecules 2004, 37, 2572–
2577.
18. Lucas, L. N.; van Esch, J.; Kellogg, R. M.; Feringa, B. L. Chem. Commun. 2001, 759–
760.
19. Kang, J.-W.; Kim, J.-J.; Kim, E. Appl. Phys. Lett. 2002, 80, 1710–1713.
20. Kang, J.-W.; Kim, J.-J.; Kim, E. Opt. Mater. 2002, 21, 543–548.
21. Myles, A. J.; Branda, N. R. Adv. Funct. Mater. 2002, 12, 167–173.
22. Hugel, T.; Holland, N. B.; Cattani, A.; Moroder, L.; Seitz, M.; Gaub, H. E. Science
2002, 296, 1103–1106.
(d, J¼7.86 Hz, 4H, arom.), 8.32 (d, J¼7.86 Hz, 4H, arom.), 7.90 (t,
J¼4.56 Hz, 1H, arom.), 7.72 (d, J¼2.2 Hz, 1H, CH-arom.), 7.40–7.43
(m, 4H, CH-arom.), 7.92 (d, J¼0.88 Hz, 1H, CH-arom.), 7.65 (dd,
J¼1.76, 1.96 Hz, 1H, 60-CH), 5.63–5.65 (m, 1H, 70-CH), 4.34 (dt,
J¼9.60, 1.76 Hz, 80-CH), 3.95 (s, 3H, 30-CH3), 3.32 (s, 3H, 20-CH3), 2.28
(s, 3H, CO–CH3), 2.23 (s, 3H, 60-CH3), 1.42 (s, 3H, 80-CH3) ppm; 13C
NMR (400 MHz, CDCl3)
d
190.48 (CO–CH3), 163.48 (30-CO), 161.95
(20-CO), 151.27, 150.46, 149.37, 143.24,140.79, 139.36, 138.89, 135.52,
132.90,131.69,129.78, 128.26, 125.36, 124.48, 124.16,122.85,120.43,
120.39, 118.78, 104.28, 96.15 (acetylenic-C), 93.62 (acetylenic-C),
82.48 (acetylenic-C), 80.23 (acetylenic-C), 65.47 (80a-C), 63.69
(spiro-C), 53.28 (30-CH3), 51.48 (20-CH3), 30.36 (CO–CH3), 22.45 (60-
23. Alonso, M.; Reboto, V.; Guiscardo, L.; San Martin, A.; Rodriguez-Cabello, G. C.
Macromolecules 2000, 33, 9480–9482.
CH3), 21.15 (80-CH3) ppm; IR (KBr):
n
¼3002–3091 (C-H, arom.),
2886–2984 (C-H, aliph.), 2212 (acetylenic bond), 1746 (30-C]O),
1703 (CO–CH3), 1682 (20-C]O), 1575 (C]N), 1463 (C]C), 1334,
1285, 1173, 1162, 965, 871, 730 cmꢁ1; MS-EI m/e (%) 788.23 [Mþ].
Elemental analysis for C51H36N2O5S: C, 77.64; H, 4.60; N, 3.55; S,
4.06. Found %: C, 77.64; H, 4.60; N, 3.54; S, 4.04.
24. (a) Wigglesworth, T. J.; Myles, A. J.; Branda, N. R. Eur. J. Org. Chem. 2005,1233–1238;
(b) Peters, A.; Vitols, C.; McDonald, R.; Branda, N. R. Org. Lett. 2002, 8, 1183–1186.
25. (a) Organic Photochromic and Thermochromic Compounds; Crano, J. C., Guglie-
metti, R. J., Eds.; Plenum: New York, NY, 1999; Vols. 1 and 2; (b) Irie, M., Ed.
Chem. Rev. 2000, 100, 1685–1716.
26. (a) Du¨rr, H.; Bouas-Laurent, H. Photochromism: Molecules and Systems; Elsevier:
Amsterdam, 1990; 2003; (b) Du¨rr, H. In Organic Photochemistry and Photobio
logy; Horspool, W. M., Song, P.-S., Eds.; CRC: Boca Raton, FL, 1995; pp 1121–
1141; (c) Du¨rr, H. In Organic Photochromic and Thermochromic Compounds;
Crano, J. C., Guglielmetti, R. J., Eds.; Plenum: New York, NY, 1999; pp 223–266.
27. (a) Du¨rr, H. Angew. Chem., Int. Ed. Engl. 1989, 28, 413–431; (b) Bleisinger, H.;
Scheidhauer, P.; Du¨rr, H.; Wintgens, V.; Valat, P.; Kossanyi, J. J. Org. Chem.1998, 63,
990–1000; (c) Gross, H.; Du¨rr, H. Angew. Chem., Int. Ed. Engl. 1982, 21, 216–217.
4.4.13. Dimethyl 2-((4-((4-((4-(acetylthio)phenyl)ethynyl)phenyl)-
ethynyl)phenyl)ethynyl)-20,4a0-dimethyl-7-((4-((4-(phenyl-
ethynyl)phenyl)ethynyl)phenyl)ethynyl)-4a0H-spiro[fluorene-9,50-
pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 18f
1H NMR (400 MHz, CDCl3)
d
8.38 (d, J¼7.60 Hz, 4H, arom.), 8.22
28. (a) Terazono, Y.; Kodis, G.; Andreasson, J.; Jeong, G.; Brune, A.; Hartmann, Th.;
Du¨rr, H.; Moore, A.; Gust, D. J. Phys. Chem. B 2004, 108, 1812–1814; (b) Kodis, G.;
Liddell, P. A.; de la Garza, L.; Clausen, P. C.; Lindsey, J. S.; Moore, A. L.; Moore, T.
A.; Gust, D. J. Phys. Chem. A 2002, 106, 2036–2048.
´
(d, J¼7.86 Hz, 4H, arom.), 8.01 (d, J¼7.86 Hz, 4H, arom.), 7.85–7.90
(m, 5H, arom.), 7.59 (d, J¼7.86 Hz, 4H, arom.), 7.46 (d, J¼7.56 Hz, 4H,
arom.), 7.58 (d, J¼2.2 Hz, 1H, CH-arom.), 7.31–7.42 (m, 4H, CH-
arom.), 7.24 (d, J¼1.00 Hz, 1H, CH-arom.), 5.43–5.45 (m, 1H, 70-CH),
4.65 (dt, J¼9.60, 1.76 Hz, 80-CH), 3.63 (s, 3H, 30-CH3), 3.39 (s, 3H, 20-
CH3), 2.28 (s, 3H, CO–CH3), 2.18 (s, 3H, 60-CH3), 1.41 (s, 3H, 80-
29. (a) Weber, C.; Rustemeyer, F.; Du¨rr, H. Adv. Mater. 1998, 10, 1348–1351; (b)
Ahmed, S. A.; Hartmann, Th.; Huch, V.; Du¨ rr, H.; Abdel-Wahab, A. A. J. Phys. Org.
Chem. 2000, 13, 539–548; (c) Tan, Y. S.; Ahmed, s. A.; Du¨rr, H.; Huch, V.; Abdel-
Wahab, A. A. Chem. Commun. 2001, 1246–1247; (d) Ahmed, S. A. Mol. Cryst. Liq.
Cryst. 2005, 430, 295–300; (e) Ahmed, S. A.; Du¨rr, H. Mol. Cryst. Liq. Cryst. 2005,
431, 275–280 (or 575–580).
CH3) ppm; 13C NMR (400 MHz, CDCl3)
d 192.00 (CO–CH3), 164.16

1388
S.A. Ahmed / Tetrahedron 65 (2009) 1373–1388
30. (a) Ahmed, S. A. Monatsh. Chem. 2004, 135, 1173–1188; (b) Ahmed, S. A.; Abdel-
Wahab, A. A.; Du¨rr, H. J. Photochem. Photobiol. 2003,154,131–144; (c) Ahmed, S. A.
J. Phys. Org. Chem. 2002,15, 392–402; (d) Ahmed, S. A. J. Phys. Org. Chem. 2006,19,
402–414; (e) Ahmed, S. A. J. Phys. Org. Chem. 2007, 20, 564–588; (h) Ahmed, S. A.;
Hartmann, T.; Durr, H. J. Photochem. Photobiol. Chem. A 2008, 200, 50–56; (i)
Ahmed, S.A.; Pozzo, J.-L. J. Photochem. Photobiol. Chem. A 2008, 200, 50–67.
31. (a) Du¨rr, H.; Schommer, C.; Mu¨nzmay, T. Angew. Chem. 1986, 25, 565–567;
Angew. Chem., Int. Ed. Engl. 1986, 25, 572–574; (b) Du¨rr, H.; Thome, A.; Kilburg,
H.; Bossmann, S.; Blasius, E.; Janzen, K.; Kranz, C. J. Phys. Org. Chem. 1992, 5,
689–698; (c) Du¨rr, H. Chimica 1994, 514–515; (d) Du¨rr, H.; Amlung, M.; Rus-
temeyer, F.; Tan, Y. S. Deutsche Offenlegungs-Schrift Pat. 1998, 198, 349–408.
32. (a) Fromm, R.; Ahmed, S. A.; Hartmann, Th.; Huch, V.; Abdel-Wahab, A. A.;
Du¨rr, H. Eur. J. Org. Chem. 2001, 21, 4077–4080; (c) Andreis, C.; Du¨rr, H.;
Wintgens, V.; Valat, P.; Kossanyi, J. Chem.dEur. J. 1997, 3, 509–516; (d) Ahmed,
S. A.; Abdel-Wahab, A. A.; Du¨ rr, H. In CRC Handbook of Organic Photochemistry
and Photobiology, 2nd ed.; Horspool, W. M., Lenci, F., Eds.; CRC: New York, NY,
2003; Chapter 96, pp 1–25.
33. (a) Du¨rr, H. Angew. Chem. 1989, 101, 427–445; Angew. Chem., Int. Ed. Engl. 1989,
28, 413–438; (b) Du¨rr, H. Wiss. Zeitschr. TH Leuna- Merseburg 1984, 26, 664–671;
(c) Du¨rr, H, Gross, H.; Zils. K.D. Deutsche Offenlegungs Schrift Pat., 32 20 275 A
1, 1983; (d) Du¨ rr. H.; Jo¨nsson, H.; Scheidhauer, P.; Mu¨nzmay, T, Spang, P.
Deutsche Offenlegungs Schrift Pat., 35214325, 1985; (e) Du¨rr, H.; Gross, H.; Zils,
K. D.; Hauck, G.; Hermann, H. Chem. Ber. 1983, 116, 3915–3925; (f) Du¨ rr, H.;
Spang, P.; Deutsche Offenlegungs Schrift Pat., 32 20 2571, 1984.
34. (a) Ahmed, S. A.; Weber, C.; Hozien, Z. A.; Hassan, Kh. M.; Abdel-Wahab, A. A.;
Du¨rr, H. Unpublished results; (b) Ahmed, S.A.; Ph.D. Thesis, Saarland-Assiut
universities, 2000; (c) Burtscher, P.; Du¨rr, H.; Rheinberger, V.; Salz, U.; German
Pat DE, 195200160, 1995; (e) Burtscher, B.; Du¨rr, H.; Rheinberger, V.; Salz. U.;
IVOCLAR German Pat., 195200160, 1995.
35. (a) Service, R. F. Science 2001, 294, 2442–2443; (b) Rodriguez, J. G.; Tejedor, J. L.;
La Parra, T.; Diaz, C. Tetrahedron 2006, 62, 3355–3361; (c) Price, D. W.; Tour, G.
M. Tetrahedron 2003, 59, 3131–3156.
36. (a) Montemerlo, M. S.; Love, G. C.; Opiteck, J. G.; Goldhaber-Gordon, G.; Ellenb-
ogen, J. C. Technologies and Designs for Electronic Nanocomputers; MITRE: McLean,
VA, 1996; (b) The International Technology Roadmap for Semiconductors (ITRS)
can be found at the URL and the nitro functionalized demonstrated the NDReffect.
38. Tour, J. M. Acc. Chem. Res. 2000, 791–804.
41. Chen, J.; Reed, M. A.; Rawlett, A. M.; Tour, J. M. Science 1999, 1550–1552.
42. Chen, J.; Wang, W.; Reed, M. A.; Rawlett, A. M.; Tour, J. M. Appl. Phys. Lett. 2000,
1224–1226.
43. Chen, J.; Wang, W.; Reed, M. A.; Rawlett, A. M.; Price, D. W.; Tour, J. M. Mater.
Res. Soc. Symp. Proc. 2001, 5582, H321–H325.
44. Acetylene Chemistry: Chemistry, Biology and Material Science; Diederich, F.,
Stang, P. J., Tykwinski, R. R., Eds.; Wiley-VCH: Weinheim, Germany, 2005.
45. Carbon-Rich Compounds: From Molecules to Materials; Haley, M. M., Tykwinski,
R. R., Eds.; Wiley-VCH: Weinheim, Germany, 2006.
46. (a) Bunz, U. H. F.; Rubin, Y.; Tobe, Y. Chem. Soc. Rev. 1999, 28, 107–119; (b)
Nielsen, M. B.; Diederich, F. Chem. Rev. 2005, 105, 1837–1867; (c) Marsden, J. A.;
Miller, J. J.; Shirtcliffe, L. D.; Haley, M. M. J. Am. Chem. Soc. 2005, 127, 2464–2476;
(d) Bowling, N. P.; Halter, R. J.; Hodges, J. A.; Seburg, R. A.; Thomas, P. S.;
Simmons, C. S.; Stanton, J. F.; McMahon, R. J. J. Am. Chem. Soc. 2006, 128, 3291–
3302.
47. (a) Cornil, J.; Beljonne, D.; Calbert, J.-P.; Bre0das, J.-L. Adv. Mater. 2001, 13, 1053–
1119; (b) Wang, C.; Batsanov, A.; Bryce, M.; Sage, I. Synthesis 2003, 13, 2089–
2095; (c) Wang, C.; Pålsson, L.-O.; Batsanov, A. S.; Bryce, M. R. J. Am. Chem. Soc.
2006, 128, 3789–3799.
48. Ahmed, S. A. Res. Lett. Org. Chem. 2008, 2008, 5 pages. Article ID 959372
49. Zarwell, S.; Ruck-Braun, K. Tetrahedron Lett. 2008, 4020–4025.
50. (a) Jian, H.; Tour, J. M. J. Org. Chem. 2003, 68, 5091–5103; (b) Wei, L.;
Tiznado, H.; Liu, G.; Padmaja, K.; Lindsey, J. S.; Zaera, F.; Bocian, D. F. J.
Phys. Chem. B 2005, 109, 23963–23971; (c) Li, Q.; Rukavishnikov, A. V.;
Petukhov, P. A.; Zaikova, T. O.; Jin, C.; Keana, J. F. W. J. Org. Chem. 2003, 68,
4862–4869.
51. Gautron, R. Bull. Soc. Chim. Fr. 1968, 3200–3204.
52. (a) Kaplan, H.; Lindwall, H. G. J. Am. Chem. Soc. 1943, 65, 927–928; (b) Tipson, R.
S. J. Am. Chem. Soc. 1945, 67, 507–511; (c) Hamer, F. M. J. Chem. Soc. 1923, 123,
246–256; (d) Gilman, H.; Karmas, G. J. Am. Chem. Soc. 1945, 67, 342.
53. (a) Hesse, M.; Meier, H.; Zeeh, B. Spektroskopische Methoden in der Organischen
Chemie; Georg Thieme: Stuttgart, New York, NY, 1995; pp 185–186.
54. (a) Perrin, D. D.; Armarego, W. L. F. Purification of Laboratory Chemicals, 3rd ed.;
Pergamon: Oxford, 1988; (b) Becker, H. G. O.; Beckert, R.; Domschke, G.; Fan-
gha¨nel, E.; Habicher, W. D.; Metz, P.; Pavel, D.; Schwetlich, K. Organikum-Or-
ganisch-chemisches Grundpraktikum, 21st ed.; Wiley-VCH: Weinheim, 2001;
Chapter F, 741–762.
¨
39. Tour, J. M.; Kozaki, M.; Seminario, J. J. Am. Chem. Soc. 1998, 8486–8493.
40. Zhou, C.; Deshpande, M. R.; Reed, M. A.; Jones, L.; Tour, J. M. Appl. Phys. Lett.
1997, 611–613.
55. Scho¨nberg, A. Praparative Organische Photochemie; Springer: Berlin, 1958;
Chapter 1.
56. Ahmed, S.A.; Pozzo. J-L.; Du¨rr, H. Under publication, 2008.