Photochromism of dihydroindolizines. Part XV: Synthesis and photophysical properties of dihydroindolizine photoswitches bearing a conjugated aryleneethynylene tripodal linker system

Article abstract of DOI:10.1007/s00706-010-0267-7

Different photochromic dihydroindolizines (DHIs) bearing conjugated aryleneethynylene tripodal linker systems were synthesized using several Sonogashira coupling reactions. The spirocyclopropene precursors incorporating different acetylenic bridge moieties at the 2-position of the fluorene moiety were synthesized via chemical and photochemical routes. Multiaddressable photochromic properties of the DHI derivatives substituted in the fluorene (region A) and pyridazine (region C) parts were studied. Optimization of the formation of the DHIs was also done by applying different palladium-mediated Sonogashira coupling reactions. Irradiation of the photochromic DHIs with polychromatic light led to colored betaines which undergo thermal 1,5-electrocyclization. The kinetics of the thermal 1,5-electrocyclization were studied by using a multichannel FT-UV-Vis spectrophotometer. A pronounced effect on the kinetic behavior of the 1,5-electrocyclization process of the betaines was observed by changing substitution from non-substituted to dimethyl-substituted pyridazines. Photodegradation experiments and the bleaching and fading cycles revealed high photostability of the betaines under investigation. These properties of betaines of tripodal linker conjugates will help these materials to find applications.

Full text of DOI:10.1007/s00706-010-0267-7

Monatsh Chem (2010) 141:357–372
DOI 10.1007/s00706-010-0267-7
ORIGINAL PAPER
Photochromism of dihydroindolizines. Part XV: Synthesis
and photophysical properties of dihydroindolizine photoswitches
bearing a conjugated aryleneethynylene tripodal linker system
•
Saleh A. Ahmed Shaya Y. Al-Raqa
Received: 19 August 2009 / Accepted: 26 January 2010 / Published online: 25 February 2010
Ó Springer-Verlag 2010
Abstract Different photochromic dihydroindolizines (DHIs)
bearing conjugated aryleneethynylene tripodal linker sys-
tems were synthesized using several Sonogashira coupling
reactions. The spirocyclopropene precursors incorporating
different acetylenic bridge moieties at the 2-position of the
fluorene moiety were synthesized via chemical and pho-
tochemical routes. Multiaddressable photochromic proper-
ties of the DHI derivatives substituted in the fluorene
(region A) and pyridazine (region C) parts were studied.
Optimization of the formation of the DHIs was also done
by applying different palladium-mediated Sonogashira
coupling reactions. Irradiation of the photochromic DHIs
with polychromatic light led to colored betaines which
undergo thermal 1,5-electrocyclization. The kinetics of
the thermal 1,5-electrocyclization were studied by using a
multichannel FT–UV–Vis spectrophotometer. A pronounced
effect on the kinetic behavior of the 1,5-electrocyclization
process of the betaines was observed by changing substitu-
tionfromnon-substituted todimethyl-substituted pyridazines.
Photodegradation experiments and the bleaching and fading
cycles revealed high photostability of the betaines under
investigation. These properties of betaines of tripodal linker
conjugates will help these materials to find applications.
Keywords Photochromism ꢀ Dihydroindolizines ꢀ
Sonogashira coupling ꢀ Aryleneethynylenes ꢀ
Tripodal linker ꢀ Photostability
Introduction
Photochromic molecules attract much attention both theo-
retically and practically because of their potential
applications in optical devices, for example optical mem-
ories and switches [1–4]. These molecules find use in the
fabrication of several optoelectronic devices, for example
optical memories, switches, and holograms. Since the last
decade, the development of such optoelectronic devices has
included photochromic compounds as the active compo-
nents [5]. It has been established that photochromic
compounds support their activities in a reversible photo-
chemical reaction induced by the absorption of electro-
magnetic radiation in the ultraviolet region, which
provokes a visible color change of the original colorless
molecule. Photochromic dihydroindolizines (DHIs), which
were discovered and developed by H. Du¨rr [6–19], are well
known photochromic materials that have attracted much
interest from the standpoints of both fundamental eluci-
dation of electrocyclization reactions and their potential
applications to optical memories and switches [20–24, 38–
44]. Because of a 1,5-electrocyclization photoisomeriza-
tion between two distinct isomeric states, i.e., the ring-
opened form (betaine form) and the ring-closed form (DHI
form), these entities are promising candidates for optical
storage media and electronic devices [38–47]. Photochro-
mic DHIs have sufficient thermal stability in both the open
and the closed forms, very high resistance to photofatigue,
and their chromophores provide convenient distinctive
groupings that absorb ultraviolet radiation and allow the
S. A. Ahmed (&) ꢀ S. Y. Al-Raqa
Chemistry Department, Faculty of Science, Taibah University,
Al-Madena Al-Mounawara 30002, Saudi Arabia
e-mail: saleh_63@hotmail.com
S. A. Ahmed
Chemistry Department, Faculty of Science, Assiut University,
Assiut 71516, Egypt
123

358
S. A. Ahmed, S. Y. Al-Raqa
reaction to be easily monitored by UV–Vis spectroscopy
[15–47].
for 8 h led to the formation of the pyrazole derivatives 7a–
7c in moderate yields (55, 52, and 49%).
Research on the synthesis of carbon-rich organic and
organometallic compounds for widespread applications in
the field of materials science has increased substantially. In
this context, the use of p-conjugated rigid fluorenyl chro-
mophores and their derivatives offers exciting perspectives
for the design of new molecular oligomeric and polymeric
materials for various optoelectronic applications [48–52].
Many molecular structures have been synthesized for use
as molecular devices, including switches, wires, control-
lers, and gates [53–57]. Within contemporary acetylene
chemistry [58], there is great interest in the synthesis of
conjugated diyne and oligoyne molecules. These carbon-
rich building blocks [59] are fundamentally important for
molecular rods and cyclic frameworks and are active
components in optoelectronic devices such as wires,
switches, and nonlinear optics, etc. [60–64].
The target spirocyclopropene derivatives 8a–8c were
obtained in low yields ranging from 19 to 32% via pho-
tolysis of the pyrazole derivatives 7a–7c. The photolysis
was carried out in an inert and dry nitrogen atmosphere
using a high pressure mercury lamp (125 W) in dry ether
solution for 2 h. The chemical structures of the synthesized
compounds 4–8 (Scheme 1) were confirmed and estab-
lished by both spectroscopic (NMR, IR, and mass
spectrometry) and elemental microanalytical data (ele-
mental analysis data were satisfactory).
Approaches to the synthesis of the p-conjugated
photochromic dihydroindolizines 10a–10f
Electrophilic addition of spirocyclopropenes 8a–8c to
pyridazine (9a) and 3,6-dimethylpyridazine (9b) using the
cyclopropene route [11–47] (Scheme 2) under dry, dark,
and inert conditions for 12 h (TLC monitored using
CH2Cl2 as eluent) led to the formation of the photochromic
DHIs 11a–11f in poor yields (22–35%, method A). For-
mation of the photochromic DHIs 11a–11f occurs through
conjugate addition of one of the nitrogen atoms of pyrid-
azines 9a, 9b to of the electron-deficient a,b-unsaturated
spirocyclopropene diester 8a–8c, which leads to ring
opening via a cyclopropyl–allyl conversion to the colored
betaines 10a–10f (Scheme 2). A subsequent ring closure to
DHIs 11a–11f results in a partial, slow, thermal 1,5-elec-
trocyclization back reaction (Scheme 2) which can be
reversed upon exposure to UV light. The photochromic
DHIs 11a–11f were obtained in the pure form by purifi-
cation on silica gel using dichloromethane as the eluent.
Alternatively, the target photochromic DHIs 11a–11f
could be synthesized via the multi-step synthesis route
shown in Scheme 3. The palladium-mediated Sonogashira
coupling of DHI 12a and its dimethyl derivative 12b [65–67]
with compounds 3a–3c (2.5% Pd(PPh3)2Cl2, CuI/Et3N, dry
THF, 5 h) yielded the desired photochromic trimethylsilyl
DHIs 13a–13f through the betaines 14a–14f, in 55–67%
isolated yields. Purification was carried out by flash chroma-
tography on silica gel with CH2Cl2 as eluent (method B).
Subsequent desilylation of the DHIs 13a–13f with tetrabu-
tylammonium fluoride (TBAF) in dry THF for 4 h afforded
the silyl-free products 15a–15f obtained in good isolated
yields (62–75%).
In continuation of our research on the synthesis and
photochromic behavior of photochromic DHIs, we now
describe the synthesis and photophysical properties of
carbon-rich fluorenyl DHI tripodal linkers and report
studies on their photochromic behavior in solution. Also,
synthesis approaches and Sonogashira-mediated method-
ologies are described in detail.
Results and discussion
Synthesis of fluorenylethynylene spirocyclopropene
precursors 8a–8c
Dimethyl 20-iodospiro[cycloprop[2]ene-1,90-fluorene]-2,3-
dicarboxylate (1) has been previously prepared by us [65–
67]. The spirocyclopropene precursors 8a (n = 0), 8b
(n = 1), and 8c (n = 2) were synthesized via a five-step
sequence, starting with the known three-step conversion of
2-nitro-9H-fluoren-9-one to 2-iodo-9H-fluoren-9-one (2) in
64% yield [68, 69 and references therein] (Scheme 1).
Sonogashira coupling of 2 with trimethylsilane derivatives
3a–3c (n = 0, 1, 2) in the presence of Pd(PPh3)2Cl2
(2.5%)/Cu2I2/Et2NH in THF for 4 h afforded the coupling
products 4a (n = 0), 4b (n = 1), and 4c (n = 2) in 74, 67,
and 59% yield, respectively. Condensation of the substi-
tuted fluorenones 4a–4c with hydrazine hydrate in boiling
ethanol for 3 h led to both condensation and desilylation
with formation of 5a (n = 0), 5b (n = 1), and 5c (n = 2)
in 61, 54, and 42% yield, respectively.
The treatment of DHIs 13a–13f with hydrazine hydrate
in ethanol at 0 °C for 1 h afforded the desilylated photo-
chromic DHIs 11a–11f in 45–59% yield (method C), which
is similar to results for compounds 4a–4c. The products
obtained from the three different routes gave the same
analytical and spectroscopic data and the same melting
points and mixed melting points.
The diazofluorene derivatives 6a–6c were obtained in
53–76% yields after oxidation of hydrazones 5a–5c with
manganese dioxide in dry ether at room temperature in the
absence of light. Addition of dimethyl acetylenedicarbox-
ylate (DMAD) to 6a–6c in dry ether under dark conditions
123

Photochromism of dihydroindolizines
359
I
COOCH3
COOCH3
1
SiMe3
H
SiMe3
I
Pd(PPh3)2Cl2
CuI / Et3N
NH2NH2
Ethanol
+
O
n
n
n
2
O
N-NH2
H
3a, n= 0
3b, n= 1
3c, n= 2
4a, n= 0
4b, n= 1
4c, n= 2
5a, n= 0
5b, n= 1
5c, n= 2
H
H
H
DMAD
Ether
MnO2
Ether
hν
n
n
n
Ether
COOCH3
N
N
N2
COOCH3
COOCH3
COOCH3
6a, n= 0
6b, n= 1
6c, n= 2
7a, n= 0
7b, n= 1
7c, n= 2
8a, n= 0
8b, n= 1
8c, n= 2
Scheme 1
Palladium-mediated Sonogashira coupling
of photochromic DHIs 11a–11f with the tripodal
linker 15 under different coupling conditions
via a Sonogashira cross-coupling reaction, under different
reaction conditions for optimization purposes (Scheme 4).
Reaction of 11a–11f with 15 under standard Sonogashira
coupling conditions (2% Pd(PPh3)2Cl2, 1% PPh3, CuI/Et3N,
THF, 15 h at 45 °C, method A) led to low conversion of
DHIs 11a–11f to the coupling products 17a–17f (22–28%).
The conditions of the Sonogashira coupling were varied by
using Pd(OAc)2/Ph3P with CuI/Et3N, toluene/DMF and
stirring for 12 h at 40 °C (method B). In this case, the
The tripodal linker 15 was prepared in six steps and 29%
overall yield in accordance with the methods reported by
Galoppini and coworkers [70–80] and Zarwell and Ru¨ck-
Braun [81]. The final fragment coupling of the photochromic
DHIs 11a–11f to the tripodal linker system 15 was surveyed,
123

360
S. A. Ahmed, S. Y. Al-Raqa
H
H
H
H
n
n
n
n
R
R
R
COOCH3
R
COOCH3
COOCH3
R
Ether
R
+ N
+
N
N
N
∆
+
-
N
24h/RT
N
N
-
COOCH3
R
N
hν
R
COOCH3
COOCH3
COOCH3
COOCH3
8a, n= 0
8b, n= 1
8c, n= 2
9a, R=H
9b, R=CH3
10a-10f
11a-11f
10'a-10'f
Scheme 2
SiMe3
SiMe3
SiMe3
R
I
R
N
hν
n
Pd(PPh3)2Cl2
CuI / Et3N
R
N
+
n
COOCH3
R
∆
COOCH3
COOCH3
n
N +
N
R
-
N
N
R
COOCH3
12a, R = H
12b, R= CH3
H
COOCH3
COOCH3
14a-14f
3a, n = 0
3b, n= 1
3c, n= 2
13a-13f
NH2NH2
(Method C)
Ethanol
TBAF/ THF
(Method B)
H
H
H
n
R
n
n
R
∆
hν
R
COOCH3
R
N
hν
N
∆
R
N +
N
N
-
N
COOCH3
COOCH3
R
COOCH3
COOCH3
COOCH3
10a-10f
11a-11f
11a-11f
Scheme 3
coupling products 17a–17f were obtained in slightly better
yields (31–52%). With the objective of further improving the
yields of 17a–17f, the reaction conditions were modified to
include bis(dibenzylideneacetone)palladium(0) as the new
palladium source, CuI, and DIEA as the base (method C),
which led to the formation of the coupling products 17a–17f
in 52–68% yield. In addition, coupling of photochromic
DHIs 11a–11f with the tripod system 15 using 2.5 or 5%
123

Photochromism of dihydroindolizines
361
O
O
H
I
O
O
O
O
O
O
n
O
O
R
+
Pd/CuI
R
N
Et3N/THF
N
COOCH3
COOCH3
O
O
11a-11f
15
n
R
COOCH3
N +
N
-
hν
H
O
O
∆
R
COOCH3
O
O
16a-16f
H
O
O
O
O
O
O
H
O
O
KOH/Ethanol
X
n
n
R
R
R
N
N
R
N
N
COOCH3
COOCH3
COOCH3
COOCH3
17a-17f
18a-18f
Scheme 4
Pd(PPh3)2Cl2, 1% 1,10-phenanthroline, 5% Nal, CuI/Et3N,
DMF at 90 °C (method D) did not afford the coupling
products 17a–17f and, instead, decomposition ofthe reaction
mixtures was observed.
Attempts to improve the yield by manipulating the per-
centage of the palladium catalyst and reaction times were
unsuccessful in all of the above mentioned coupling reac-
tions. Interestingly, the photochromic DHIs 17a and 17d
were previously synthesized by us [67] via a Sonogashira
cross-coupling reaction by coupling of halo-substituted
DHI with an acetylenic tripodal system which resulted in
exactly the same chemical structures.
Also the coupling reaction of DHIs 11a–11f and the
tripodal linker 15 using Pd(PPh3)4 in dry pyrrolidine at
45 °C for 8 h (RT and 60 °C were also used) showed no
evidence of the formation of the coupling products 17a–17f
(method E). This copper-free method was investigated to
circumvent the homo-dimerization of the DHI system.
Attempted hydrolysis of the methyl ester groups of
DHIs 17a–17f using KOH in ethanol or THF at room
123

362
S. A. Ahmed, S. Y. Al-Raqa
DHIs 11a–11f, 13a–13f, and 17a–17f showed yellow color
in dichloromethane solution and in the solid state (Table 1).
The intensities (log e) of the absorption of these bands were
found to lie between 3.80 and 4.67 depending on the number
of aryleneethynylene groups. The absorption of DHIs 11a–
11f, 13a–13f, and 17a–17f were observed in the far UV
region and showed absorption maxima between 390 and
405 nm (Table 1). This absorption depends on the number
of aryleneethynylene groups substituting the aromatic fluo-
rene (region A). A pronounced bathchromic shift of about
6 nm was recorded after coupling of DHIs 11a–11f with the
tripodal system 15, as in DHIs 17a–17f. This may be
attributed to the increase in extended conjugation of the DHI
skeleton following coupling. Exchanging the proton on the
pyridazine with a methyl substituent led to a bathochromic
shift of about 3 nm of the DHIs 17d–17f. These absorption
bands can be assigned to the locally excited p–p*-transition
(LE) located in the butadienyl-vinylamine chromophores
[11–47] of the photochromic DHIs 11a–11f, 13a–13f, and
17a–17f (Table 1).
Fig. 1 Representation of the optimized (MM2) structure of DHI 17c
temperature and at 50 °C afforded no product and instead
decomposition of the DHIs was observed. All subsequent
attempts to obtain the tricarboxylic acids 18a–18f by
changing base concentration (4–8 M) and reaction times
(from RT to 72 h, in ethanol or in THF) were met with
failure. The chemical structures of all photochromic DHIs
11a–11f, 13a–13f, and 17a–17f were established on the
basis of spectral and analytical data which corroborated the
suggested chemical structures. For example, the chemical
structure of DHI 17c was assigned by 2D NMR spectros-
copy. Further assignments of 80-CH, 80a-CH, and some
other protons in the DHI skeleton were achieved with the
aid of a NOESY spectrum of 17c. We observed that 80a-CH
at d = 4.94 ppm is proximal to 80-CH at d = 5.35 ppm
and 1-CH of the fluorene moiety at d = 7.68 ppm. This
suggests that 80a-CH is in the 80a-position and not the
80-position. Indeed, the connectivity between 80-CH and
8-CH of the fluorene part at d = 7.54 ppm was observed.
This vicinity of 80-CH with 8-CH indicates that the pyr-
idazine moiety is perpendicular to the fluorene skeleton.
This observation is also supported by molecular modeling
calculation of DHI 17a (Fig. 1). The molecular mechanics
calculation (MM2) showed that the distance between both
80a-CH and 80-CH connected to 60-CH and 1-CH of the
Polychromatic light irradiation of DHIs 11a–11f, 13a–
13f, and 17a–17f led to the ring-opened betaines 10a–10f,
14a–14f, and 16a–16f (Fig. 2). The colored betaine forms
10a–10f, 14a–14f, and 16a–16f changed from red to blue-
green in CH2Cl2 solution, at
a concentration of
1910-5 mol dm-3, at room temperature because of their
slower 1,5-electrocyclization. All absorption maxima of
the colored betaines 10a–10f, 14a–14f, and 16a–16f were
found in the visible region between 522 nm (betaine 11a)
and 635 nm (betaine 17f). The UV spectra of the colored
betaines containing a non-substituted pyridazine as a het-
erocyclic moiety, as in betaines 10a–10c, 14a–14c, and
16a–16c (Fig. 2), exhibit a red-violet color and show only
one absorption maximum ranging between 522 and
534 nm. On the other hand, the betaines containing a
dimethylpyridazine in region C (10d–10f, 14d–14f, and
16d–16f) showed a green–blue color and three absorption
maxima with three isobestic points (Table 1). Interestingly,
a bathochromic shift by more than 110 nm was observed in
the absorption spectra of the betaines containing non-
substituted pyridazines 10a–10c, 14a–14c, and 16a–16c
compared with the dimethyl analogs 10d–10f, 14d–14f,
and 16d–16f. This large shift led to the change of the
colored forms from red to green–blue, which is attributed
to the hyper-conjugation bestowed by the two methyl
groups which imparts stability to the zwitterionic betaines
leading to a bathochromic shift [65–67] (Table 1). Fur-
thermore, a noticeable bathochromic shift of about 7–9 nm
was noted by increasing the number of bridged phenyl
acetylenic groups from n = 0 to n = 2 which showed no
dependence on the substitution pattern of the pyridazine.
This may be attributed to an increase in the conjugation of
the fluorene unit via hyperconjugation with the aromatic
˚
fluorene moiety is\3 A, which is in good agreement with
the NMR results (Fig. 1).
Absorption spectra of DHIs 11a–11f, 13a–13f,
and 17a–17f, and their corresponding betaines
10a–10f, 14a–14f, and 16a–16f
The photophysical properties pertinent to their photochro-
mic properties were obtained from the absorption features of
photochromic DHIs 11a–11f, 13a–13f, and 17a–17f. The
absorption spectra of the synthesized DHIs 11a–11f, 13a–
13f, and 17a–17f were measured in dichloromethane solu-
tion, at a concentration of 1 9 10-5 mol dm-3, at 23 °C,
using a UV–Vis spectrophotometer. The photochromic
123

Photochromism of dihydroindolizines
363
Table 1 Absorption spectra of DHIs 11a–11f, 13a–13f, and 17a–17f
and their corresponding betaines 10a–10f, 14a–14f, and 16a–16f, and
kinetic data of betaines 10a–10f, 14a–14f, and 16a–16f in the second
range (monitored by UV spectrophotometry) in CH2Cl2 solution
(23 °C, c = 1910-5 mol dm-3
)
DHI/Betaine
kmax (DHI) (nm)
log (e)
kmax (betaine) (nm)
k 910-3 (s)
t1/2 (s)
Color of betaine
11a/10a
11b/10b
11c/10c
11d/10d
11e/10e
11f/10f
385
386
387
398
399
401
391
393
394
395
399
402
402
403
405
406
407
407
3.82
3.85
4.96
4.02
4.09
4.13
3.87
3.89
3.96
4.03
4.07
4.13
4.22
4.28
4.35
4.34
4.46
4.52
522
3.50
3.22
3.04
1.03
0.69
0.64
6.54
5.10
3.96
1.11
8.22
7.40
2.57
2.42
2.31
0.49
0.46
0.41
198
215
Red–violet
Red–violet
Red–violet
Green–blue
Green–blue
Green–blue
Red–violet
Red–violet
Red–violet
Red–violet
Green
523
523
228
354, 444, 626
355, 445, 628
355, 448, 630
527
675
995
1,083
106
13a/14a
13b/14b
13c/14c
13d/14d
13e/14e
13f/14f
17a/16aa
17b/16b
17c/16c
17d/16da
17e/16e
17f/16f
529
136
532
175
355, 449, 627
357, 445, 626
352, 445, 634
529
624
843
937
Green
270
Red–violet
Red–violet
Red–violet
Green–blue
Green–blue
Green–blue
532
287
534
300
353, 442, 632
355, 447, 632
355, 448, 635
1,413
1,521
1,678
a
The photochromic data of DHIs 17a, 17d have been reported elsewhere [65–67] and are cited here for comparison
2.0
4.0
1.8
523 nm
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
DHI 11c
betaine 10c
387 nm
Betaine form
529nm
DHI form
393nm
300
350
400
450
500
550
600
650
700
750
250
300
350
400
450
500
550
600
650
700
750
Wavelength/nm
Wavelength/nm
Fig. 2 UV–Vis of photochromic DHI 11c and the corresponding
betaine form 10c after UV irradiation in CH2Cl2 (c = 1910-5 mol dm-3
at ambient temperature
Fig. 3 FT–UV–Vis kinetic spectra of the 1,5-electrocylization of the
betaine 14b to DHI 13b (cycle time = 50 s, run time = 400 s) in
CH2Cl2 (c = 1910-5 mol dm-3 at 253 K)
)
phenyl rings through the bridged acetylenic bond. Indeed, a
bathochromic shift of about 10 nm of the absorption of the
betaines 16a–16f incorporating the tripod linker conjugate
compared with the betaines 10a–10f and 14a–14f incor-
porating no tripodal linker conjugates was detected. More
spectroscopic data about the UV–Vis measurements of the
colored betaines under investigation are listed in Table 1.
The kinetics of the thermal 1,5-electrocyclization of the
betaine forms 10a–10f, 14a–14f, and 16a–16f were studied
by use of a multichannel FT–UV–Vis spectrophotometer
(Figs. 3, 4). The thermal fading back reaction measure-
ments showed that the half-lives of the colored betaines
10a–10f, 14a–14f, and 16a–16f lie in the second domain
and were found to be between 106 and 1,678 s (Table 1
123

364
S. A. Ahmed, S. Y. Al-Raqa
2.2
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
Table 2 Photodegradation data of some selected betaines 10a–10f,
14a–14f, and 16a–16f in dichloromethane solution (c = 1
10-5 mol dm-3) at 23 °C
9
Betaine form
448 nm
DHI form
407 nm
Betaine t30 betaine/DHI
F
Betaine t30 betaine/DHI F
Betaine form
635 nm
10a
10b
10c
10d
10e
10f
518
464
419
559
520
499
461
433
362
2.13 14d
1.91 14e
1.72 14f
2.30 16aa
2.14 16b
2.05 16c
1.90 16da
1.78 16e
1.49 19f
498
451
436
583
533
461
694
599
512
2.05
1.86
1.79
2.40
2.19
1.90
2.86
2.47
2.11
1.00
355 nm
14a
14b
14c
Standard 243
1.00 Standard 243
300
400
500
600
700
800
900
a
Wavelength/nm
The photodegradation data of betaines 16a, 16d have been reported
previously [65–67] and are cited here for comparison. The factor F is
the ratio between the t30 value of the betaine under investigation and
the standard betaine (dicyanopyridazine DHI)
Fig. 4 FT–UV–Vis kinetic spectra of the 1,5-electrocyclization of
the betaine 16f to DHI 17f (cycle time = 500 s, run time = 4,000 s)
in CH2Cl2 (c = 1910-5 mol dm-3 at 253 K)
and Figs. 3, 4). A pronounced increase in the half-lives of
the betaines bearing a dimethylpyridazine 10d–10f, 14d–
14f, and 16d–16f by approximately a factor of 7 compared
with the half-lives of the betaines bearing a non-substituted
pyridazine 10a–10c, 14a–14c, and 17a–17c was observed.
As previously discussed [65–67], the detected increase in
the half-lives may be attributed to the stabilization of the
positive and negative charges on the betaine forms leading
to enhancement of the half-lives of the betaine structures
by the electron-donating methyl groups. Elongation of the
half-lives of the betaine forms by increasing the number of
acetylenic units in the bridge by approximately a factor of
1.30 was recorded. Also, a noticeable rise in the half-lives
of the betaines coupled with tripodal linker system as in
16a–16f compared with non-coupled betaines 10a–10f and
14a–14f was observed. These increases and tuning of the
absorption spectra and half-lives of the tripodal DHIs will
help these materials to be supported on metal oxide
nanoparticles.
110
100
90
80
70
betaine10a
betaine10b
betaine10d
60
50
40
30
20
10
0
betaine10e
betaine14b
betaine14c
betaine14e
betaine14f
betaine16b
betaine16c
betaine16e
betaine16f
0
100
200
300
Time/min
400
500
600
700
Fig. 5 Photodegradation experiment for determination of the t30
value of selected betaines 10a–10f, 14a–14f, and 16a–16f in CH2Cl2
(c = 1910-5 mol dm-3) at ambient temperature
-
Photo-degradation resistance of photochromic DHIs
11a–11f, 13a–13f, 17a–17f and their corresponding
betaines 10a–10f, 14a–14f, 16a–16f
13f, 17a–17f at room temperature (23 °C) with polychro-
matic light (k = 200–400 nm) led to the ring-opened
colored betaines 10a–10f, 14a–14f, and 16a–16f. Upon
continued irradiation they decomposed after some time.
The time in which the absorbance reaches 30% of its initial
value is called t30 value.
The gradual loss of the ability to change color by exposure
to visible or ultraviolet light in this context has been termed
fatigue [1–4, 11–14]. Gautron [82] has advanced a quan-
titative approach to measure fatigue in photochromic
systems. Because of the slow thermal bleaching process of
the betaines to DHIs, FT–UV–Vis measurement at room
temperature was used to study the photo-fatigue of the
DHIs and betaines under investigation. Irradiation of
degassed dichloromethane solution of DHIs 11a–11f, 13a–
The photodegradation data represented in Table 2 and
Fig. 5 show that most of the selected betaines under
investigation showed a higher photo-fatigue resistance than
the standard dicyano-pyridazine DHI (t30 = 243 min) by a
factor between 1.72 as in the case of betaine 10c and 2.86
as in the case of betaine 16d. A noticeable decrease in the
123

Photochromism of dihydroindolizines
365
t
30 values by increasing the number of acetylenic bridges in
tripodal linker conjugate based photochromic DHI deriva-
tives were synthesized successfully through different
pathways to optimize reaction conditions and yields. Many
coupling reactions were done on the fluorene part (region
A) with different phenyl acetylenic bridges to help the
extension of the photochromism of target molecules for
future applications in electronic devices, molecular wires,
and solar energy conversion using different alternative
routes. Interesting photochromic properties with tuning of
the chemical structures of the photochromic DHIs by
changing the number of acetylenic bridges in the fluorene
part and substitutions in the pyridazine region were
detected. The photodegradation measurements of the pho-
tochromic DHIs and their corresponding betaines under
investigation showed a higher photo-fatigue resistance by
direct irradiation or by cycling between colored and col-
orless forms than the standard dicyano-DHI system. The
multi-addressable photochromic properties of the new
studied photochromic DHIs and their corresponding beta-
ines are expected to be helpful in finding suitable
applications.
both betaines bearing two methyl groups and the non-
substituted pyridazines was recorded. A highly pronounced
increase in the t30 values of the betaines incorporating
dimethylpyridazine as in betaines 10d–10f, 14d–14f, and
16d–16f compared with the betaines incorporating a non-
substituted pyridazine as in betaines 10a–10c, 14a–14c,
and 16a–16c by factor of about 0.1–0.3 has been observed.
Interestingly, betaines 16a–16f incorporating a tripodal
linker showed the highest t30 values compared with other
betaines under investigation. This interesting phenomenon
will help these promising compounds find their applica-
tions. Betaine 16d (t30 = 694 min) substituted with two
methyl groups in the pyridazine moiety showed the highest
photo-fatigue resistance amongst the other studied betaines
and more than the standard betaine (t30 = 243 min) by a
factor of 2.86.
The irradiation and thermal fading measurements pre-
sented in Fig. 6 show that the DHI/betaine 17e/16e bearing
the tripod linker system is more stable than the DHI/betaine
13e/14e in terms of bleaching the thermal fading processes.
The 20 bleaching and thermal fading cycles studied
revealed no evidence of any decomposition product of the
DHI/betaine 17e/16e, as indicated by the UV–Vis mea-
surements. These results have been further supported by
NMR measurements which showed superimposable NMR
spectra (coupling, d values, and intensities) of the DHIs
before irradiation and after 20 cycles of irradiation with no
detection of any decomposition products.
Experimental
Fluorenespirocyclopropene derivatives 8a–8c were ob-
tained via photolysis of the corresponding pyrazoles in the
photochemical reactor of Schenck [83] made from Pyrex
(k [ 290 nm) according to reported procedures [15–53]. A
high-pressure mercury lamp Philips–HPK (125 W) was
used as a source of irradiation and the photolysis time was
4 h. Photochromic DHIs 17a and 17d were previously
prepared by us [65–67]. The tripod linker system was
prepared following the reaction procedures published by
Galoppini and coworkers [70–80] and Zarwell and Ru¨ck-
Braun [81]. Trimethylsilyl acetylene derivatives 2a–2c
were prepared following the reaction procedures published
by Rodriguez et al. [48–50, 68, 69]. Solutions to be
photolyzed were flushed with dry nitrogen for 30 min
before switching on the UV lamp. The progress of the
reaction and the purity of the products isolated were
monitored using TLC. Separation and purification of all
synthesized photochromic materials were carried out using
column chromatography (100 9 2 cm) on silica gel and
CH2Cl2 as eluent. An Electrothermal Engineering melting-
point apparatus was used to determine melting points. All
NMR spectra were collected on a Bruker DRX 400 spec-
trometer (400 MHz) in CDCl3 using TMS as the internal
standard. Chemical shifts (d) are reported in ppm. FT-IR
measurements were performed using a Shimadzu FT-
IR-8400S Fourier-transform infrared spectrophotometer.
Mass spectra were recorded on a VG AutoSpec apparatus
using electron impact at 70 eV. MALDI-MS spectra were
In conclusion, we have described different palladium-
mediated Sonogashira coupling reactions to optimize the
coupling reactions with different acetylenic bridges and
with the tripod linker system. Carbon-rich molecules and
1.8
DHI/Betaine 13e/14e
1.7
1.6
1.5
1.4
1.3
1.2
1.1
1.0
0.9
0.8
DHI/Betaine 17e/16e
Betaine 16e
DHI 17e
Betaine 14e
DHI 13e
0
5
10
15
20
25
30
35
40
45
50
Irradiation/ thermal fading cycles
Fig. 6 Irradiation and thermal fading of DHI/betaine 14e/13e and
DHI/betaine 17e/16e (irradiation/thermal fading/irradiation cycles) in
CH2Cl2 (c = 1910-5 mol dm-3) at ambient temperature
123

366
S. A. Ahmed, S. Y. Al-Raqa
recorded in the positive mode using 2,5-dihydroxybenzoic
acid in dioxane as matrix. UV-spectra were recorded on a
Jasco V-570 FT-UV–Vis computerized spectrophotometer.
All synthesized compounds gave satisfactory elemental
analysis data. Compounds 17a and 17d are identical with
those reported in Refs. [65–67].
was extracted three times with 20 cm3 ethyl acetate, and
the residue was purified by column chromatography using
dichloromethane as eluent to afford the required com-
pounds 11a–11f as yellow solids.
Dimethyl2-ethynylspiro[9H-fluorene-9,50(40aH)-pyrrolo[1,2-
b]pyridazine]-60,70-dicarboxylate (11a, C25H18N2O4)
Method A: yield 35%, m.p.: 177 °C; method B: yield 75%,
m.p.: 177 °C; method C: yield 75%, m.p.: 176 °C; 1H
NMR (400 MHz, CDCl3): d = 7.91–7.92 (d, J = 2.4 Hz,
1H, CH arom.), 7.87–7.89 (d, J = 2.4 Hz, 1H, CH arom.),
7.75–7.76 (d, J = 1.89 Hz, 1H, CH arom.), 7.49–7.52 (d,
J = 2.4 Hz, 1H, CH arom.), 7.45–7.47 (d, J = 2.4 Hz, 1H,
CH arom.), 7.40–7.42 (dd, J = 1.76 Hz, J = 1.98 Hz,
1H, 60-CH), 7.30–7.33 (dt, J = 2.4 Hz, J = 0.88 Hz, 1H,
CH arom.), 7.21–7.23 (dt, J = 2.4 Hz, J = 0.88 Hz, 1H,
CH arom.), 5.72–5.74 (m, 1H, 70-CH), 4.99–5.02 (t,
J = 2.2 Hz, 1H, 80-CH), 4.71–4.74 (dt, J = 9.60 Hz,
J = 1.76 Hz, 80-CH), 4.09 (s, 1H, acetylenic H), 3.87 (s,
3H, 30-CH3), 3.45 (s, 3H, 20-CH3) ppm; 13C NMR
(100 MHz, CDCl3): d = 163.42 (30-CO), 161.79 (20-CO),
149.23, 146.22, 142.97, 141.03, 140.19, 138.43, 136.02,
132.99, 130.62, 128.67, 126.76, 123.32, 122.46, 121.84,
120.34, 118.38, 104.48, 82.46 (acetylenic C), 81.34
(acetylenic C), 62.31 (80a-C), 59.34 (spiro-C), 53.34
General procedures for the synthesis of dimethyl
2-[ethynyl(phenylethynyl)n]spiro[9H-fluorene-
9,50(40aH)-pyrrolo[1,2-b]pyridazine]-60,70-
dicarboxylates 11a–11f
Method A. A solution of spirocyclopropenes 8a–8c
(0.5 mmol) in 30 cm3 dry ether and pyridazine (9a) or
3,6-dimethylpyridazine (9b) (0.7 mmol) were stirred at
room temperature under dry N2 in the absence of light for
12 h (TLC controlled). Ether was removed under reduced
pressure and the products were purified by twice repeated
column chromatography on silica gel using dichloro-
methane as eluent; finally recrystallization from the
appropriate solvents afforded the products as pale yellow
crystals.
Method B. To a solution of 2-iodopyridazine DHIs 12a
or 12b (0.55 mmol) and trimethylsilylacetylene (3a), ((4-
ethynylphenyl)ethynyl)trimethylsilane (3b), or ((4-((4-
ethynylphenyl)ethynyl)phenyl)ethynyl)trimethylsilane (3c)
(1.25 mmol) in 20 cm3 dry THF and 50 cm3 freshly
distilled triethylamine under argon atmosphere at 50 °C
was added dichlorobis(triphenylphosphine) palladium
(19 mg, 0.026 mmol) and copper iodide (1.1 mg,
0.008 mmol). The mixture was stirred for 5 h, then the
amine and THF were removed under reduced pressure.
The crude residue was washed with saturated aqueous
ammonium chloride solution (3 9 20 cm3) with a small
amount of KCN (200 mg), and extracted with dichloro-
methane (3 9 20 cm3). The extracts were dried over
anhydrous sodium sulfate and the solvent was removed to
give a brown solid, which was purified by column chro-
matography to afford the trimethylsilylated DHIs 13a–
13f. The DHIs 13a–13f (0.14 mmol) were dissolved in
10 cm3 freshly distilled dry THF and treated with a
solution of tetrabutylammonium fluoride (TBAF, 0.150 g,
1.1 mmol) in 5 cm3 freshly distilled THF at room tem-
perature under nitrogen atmosphere. The reaction mixture
was stirred for 4 h, then 10 cm3 water was added. The
mixture was extracted with ethyl acetate (3 9 20 cm3)
and the residue was purified by column chromatography
using dichloromethane as eluent to afford the required
compounds 11a–11f as yellow solids.
0
0
ꢀ
(3 -CH3), 51.46 (2 -CH3) ppm; IR (KBr): m = 3,076–
3,043 (C–H, arom.), 2,887–2,972 (C–H, aliph.), 2,162
(acetylenic bond), 1,741 (30-C=O), 1,694 (20-C=O), 1,585
(C=N), 1,432 (C=C), 1,357, 1,252, 1,179, 1,080, 953, 875,
760 cm-1; MS: m/z = 410.13 [M?].
Dimethyl 2-[(4-ethynylphenyl)ethynyl]spiro[9H-fluorene-
9,50(40aH)-pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate
(11b, C33H22N2O4)
Method A: yield 28%, m.p.: 164 °C; method B: yield 57%,
m.p.: 165 °C; method C: yield 52%, m.p.: 163 °C; 1H
NMR (400 MHz, CDCl3): d = 7.88–7.90 (d, J = 2.4 Hz,
1H, CH arom.), 7.87–7.89 (d, J = 2.4 Hz, 1H, CH arom.),
7.75–7.76 (d, J = 1.89 Hz, 1H, CH arom.), 7.56–7.58 (d,
J = 7.98 Hz, 2H, CH arom.), 7.50–7.53 (d, J = 7.98 Hz,
2H, CH arom.), 7.45–7.47 (d, J = 2.4 Hz, 1H, CH arom.),
7.42–7.43 (d, J = 2.4 Hz, 1H, CH arom.), 7.39–7.41
(dd, J = 1.76 Hz, J = 1.98 Hz, 1H, 60-CH), 7.29–7.32 (dt,
J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.), 7.23–7.25 (dt,
J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.), 5.70–5.73 (m,
1H, 70-CH), 4.96–4.98 (t, J = 2.2 Hz, 1H, 80a-CH), 4.70–
4.73 (dt, J = 9.60 Hz, J = 1.76 Hz, 80-CH), 4.05 (s, 1H,
acetylenic H), 3.82 (s, 3H, 30-CH3), 3.42 (s, 3H, 20-CH3)
13
ppm; C NMR (100 MHz, CDCl3): d = 163.42 (30-CO),
161.79 (20-CO), 149.23, 146.22, 142.97, 141.03, 140.19,
138.43, 136.02, 132.99, 131.56, 130.62, 128.67, 126.76,
123.32, 122.46, 121.84, 120.34, 118.38, 104.48, 93.12
(acetylenic C), 89.65 (acetylenic C), 82.46 (acetylenic C),
81.31 (acetylenic C), 62.30 (80a-C), 59.35 (spiro-C), 53.39
Method C. A solution of DHIs 13a–13f (0.25 mmol) and
hydrazine hydrate (99%, 0.1 cm3, 2 mmol) in 10 cm3
absolute ethanol was cooled to 0 °C and stirred at this
temperature for 1 h. The solvent was removed, the product
123

Photochromism of dihydroindolizines
367
(30-CH3), 51.41 (20-CH3) ppm; IR (KBr): ꢀm = 3,100–3,025
(C–H, arom.), 2,890–2,987 (C–H, aliph.), 2,154 (acetylenic
bonds), 1,739 (30-C=O), 1,692 (20-C=O), 1,581 (C=N),
1,437 (C=C), 1,349, 1,254, 1,172, 1,081, 953, 877,
757 cm-1; MS: m/z = 510.16 [M?].
(acetylenic C), 63.26 (80a-C), 59.31 (spiro-C), 53.39 (30-
CH3), 51.25 (20-CH3), 22.46 (60-CH3), 21.22 (80-CH3) ppm;
ꢀ
IR (KBr): m = 3,091–3,013 (C–H, arom.), 2,846–2,979 (C–
H, aliph.), 2,167 (acetylenic bond), 1,747 (30-C=O), 1,693
(20-C=O), 1,585 (C=N), 1,438 (C=C), 1,363, 1,250, 1,187,
1,082, 950, 878, 766 cm-1; MS: m/z = 438.16 [M?].
Dimethyl 2-[[4-[(4-ethynylphenyl)ethynyl]phenyl]ethynyl]-
spiro[9H-fluorene-9,50(40aH)-pyrrolo[1,2-b]pyridazine]-
60,70-dicarboxylate (11c, C41H26N2O4)
Dimethyl (40aS)-2-[(4-ethynylphenyl)ethynyl]-20,40a-di-
methylspiro[9H-fluorene-9,50(40aH)-pyrrolo[1,2-b]pyrida-
zine]-60,70-dicarboxylate (11e, C35H26N2O4)
Method A: yield 27%, m.p.: 144 °C; method B: yield 65%,
m.p.: 143 °C; method C: yield 50%, m.p.: 143 °C; 1H
NMR (400 MHz, CDCl3): d = 7.85–7.86 (d, J = 2.4 Hz,
1H, CH arom.), 7.86–7.88 (d, J = 2.4 Hz, 1H, CH arom.),
7.74–7.75 (d, J = 1.89 Hz, 1H, CH arom.), 7.56–7.58 (m,
6H, CH arom.), 7.50–7.53 (d, J = 7.98 Hz, 2H, CH arom.),
7.44–7.46 (d, J = 2.4 Hz, 1H, CH arom.), 7.40–7.42 (d,
J = 2.4 Hz, 1H, CH arom.), 7.36–7.38 (dd, J = 1.76 Hz,
J = 1.98 Hz, 1H, 60-CH), 7.30–7.33 (dt, J = 2.4 Hz,
J = 0.88 Hz, 1H, CH arom.), 7.24–7.25 (dt, J = 2.4 Hz,
J = 0.88 Hz, 1H, CH arom.), 5.71–5.74 (m, 1H, 70-CH),
4.95–4.97 (t, J = 2.2 Hz, 1H, 80a-CH), 4.75–4.78 (dt,
J = 9.60 Hz, J = 1.76 Hz, 80-CH), 4.07 (s, 1H, acetylenic
H), 3.84 (s, 3H, 30-CH3), 3.45 (s, 3H, 20-CH3) ppm; 13C
NMR (100 MHz, CDCl3): d = 163.36 (30-CO), 161.85 (20-
CO), 149.13, 146.01, 143.10, 141.63, 140.23, 138.68,
136.00, 132.95, 131.95, 131.51, 130.69, 128.60, 126.79,
123.30, 122.44, 121.91, 120.37, 118.36, 104.54, 93.23
(acetylenic C), 89.77 (acetylenic C), 82.47 (acetylenic C),
81.43 (acetylenic C), 62.37 (80a-C), 59.36 (spiro-C), 53.43
Method A: yield 24%, m.p.: 133 °C; method B: yield 68%,
m.p.: 134 °C; method C: yield 49%, m.p.: 133 °C; 1H
NMR (400 MHz, CDCl3): d = 7.85–7.87 (d, J = 2.4 Hz,
1H, CH arom.), 7.82–7.81 (d, J = 2.4 Hz, 1H, CH arom.),
7.71–7.74 (d, J = 1.89 Hz, 1H, CH arom.), 7.57–7.61 (d,
J = 7.98 Hz, 2H, CH arom.), 7.54–7.56 (d, J = 7.98 Hz,
2H, CH arom.), 7.44–7.46 (d, J = 2.4 Hz, 1H, CH arom.),
7.40–7.43 (d, J = 2.4 Hz, 1H, CH arom.), 7.30–7.34 (dt,
J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.), 7.24–7.26 (dt,
J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.), 5.76–5.80 (m,
1H, 70-CH), 4.74–4.77 (dt, J = 9.60 Hz, J = 1.76 Hz, 80-
CH), 4.04 (s, 1H, acetylenic H), 3.80 (s, 3H, 30-CH3), 3.47
(s, 3H, 20-CH3), 2.14 (s, 3H, 60-CH3), 1.42 (s, 3H, 80a-CH3)
13
ppm; C NMR (100 MHz, CDCl3): d = 163.58 (30-CO),
161.92 (20-CO), 149.26, 146.20, 143.03, 141.13, 140.34,
138.45, 136.12, 132.87, 131.54, 130.56, 128.64, 126.71,
123.31, 122.44, 121.83, 120.34, 118.33, 104.44, 93.10
(acetylenic C), 89.64 (acetylenic C), 82.44 (acetylenic C),
81.37 (acetylenic C), 62.32 (80a-C), 59.37 (spiro-C), 53.30
(30-CH3), 51.47 (20-CH3), 22.45 (60-CH3), 21.29 (80a-CH3)
ppm; IR (KBr): ꢀm = 3,096–3,012 (C–H, arom.), 2,880–
2,981 (C–H, aliph.), 2,150 (acetylenic bonds), 1,743
(30-C=O), 1,690 (20-C=O), 1,582 (C=N), 1,440 (C=C),
1,352, 1,250, 1,167, 1,089, 950, 889, 765 cm-1; MS:
m/z = 538.19 [M?].
0
0
ꢀ
(3 -CH3), 51.46 (2 -CH3) ppm; IR (KBr): m = 3,100–3,019
(C–H, arom.), 2,890–2,982 (C–H, aliph.), 2,157 (acetylenic
bonds), 1,749 (30-C=O), 1,694 (20-C=O), 1,576 (C=N),
1,476 (C=C), 1,353, 1,257, 1,136, 1,088, 967, 871,
763 cm-1; MS: m/z = 610.19 [M?].
Dimethyl (40aS)-2-ethynyl-20,40a-dimethylspiro[9H-fluo-
rene-9,50(40aH)-pyrrolo[1,2-b]pyridazine]-60,70-dicarbox-
ylate (11d, C27H22N2O4)
Dimethyl (40aS)-2-[[4-[(4-ethynylphenyl)ethynyl]phenyl]-
ethynyl]-20,40a-dimethylspiro[9H-fluorene-9,50(40aH)-pyr-
rolo[1,2-b]pyridazine]-60,70-dicarboxylate
Method A: yield 26%, m.p.: 146 °C; method B: yield 63%,
m.p.: 145 °C; method C: yield 54%, m.p.: 144 °C; 1H
NMR (400 MHz, CDCl3): d = 7.95–7.97 (d, J = 2.4 Hz,
1H, CH arom.), 7.84–7.86 (d, J = 2.4 Hz, 1H, CH arom.),
7.73–7.75 (d, J = 1.89 Hz, 1H, CH arom.), 7.50–7.54 (d,
J = 2.4 Hz, 1H, CH arom.), 7.47–7.49 (d, J = 2.4 Hz,
1H, CH arom.), 7.37–7.40 (dt, J = 2.4 Hz, J = 0.88
Hz, 1H, CH arom.), 7.18–7.22 (dt, J = 2.4 Hz, J =
0.88 Hz, 1H, CH arom.), 5.60–5.63 (m, 1H, 70-CH),
4.78–4.81 (dt, J = 9.60 Hz, J = 1.76 Hz, 80-CH), 4.06
(s, 1H, acetylenic H), 3.84 (s, 3H, 30-CH3), 3.44 (s, 3H, 20-
CH3), 2.11 (s, 3H, 60-CH3), 1.43 (s, 3H, 80a-CH3) ppm; 13C
NMR (100 MHz, CDCl3): d = 164.00 (30-CO), 161.98 (20-
CO), 149.26, 146.46, 143.89, 141.64, 140.19, 138.76,
136.36, 133.06, 130.66, 128.46, 126.76, 123.47, 122.63,
121.88, 120.42, 118.37, 104.52, 82.42 (acetylenic C), 81.36
(11f, C43H30N2O4)
Method A: yield 22%, m.p.: 121 °C; method B: yield 62%,
m.p.: 120 °C; method C: yield 45%, m.p.: 120 °C; 1H
NMR (400 MHz, CDCl3): d = 7.88–7.91 (d, J = 2.4 Hz,
1H, CH arom.), 7.85–7.87 (d, J = 2.4 Hz, 1H, CH arom.),
7.76–7.78 (d, J = 1.89 Hz, 1H, CH arom.), 7.54–7.59 (m,
6H, CH arom.), 7.51–7.53 (d, J = 7.98 Hz, 2H, CH arom.),
7.42–7.45 (d, J = 2.4 Hz, 1H, CH arom.), 7.38–7.41 (d,
J = 2.4 Hz, 1H, CH arom.), 7.32–7.35 (dt, J = 2.4 Hz,
J = 0.88 Hz, 1H, CH arom.), 7.20–7.24 (dt, J = 2.4 Hz,
J = 0.88 Hz, 1H, CH arom.), 5.78–5.82 (m, 1H, 70-CH),
4.72–4.76 (dt, J = 9.60 Hz, J = 1.76 Hz, 80-CH), 4.04 (s,
1H, acetylenic H), 3.82 (s, 3H, 30-CH3), 3.44 (s, 3H, 20-
CH3), 2.18 (s, 3H, 60-CH3), 1.44 (s, 3H, 80a-CH3) ppm; 13C
NMR (100 MHz, CDCl3): d = 163.45 (30-CO), 161.84 (20-
123

368
S. A. Ahmed, S. Y. Al-Raqa
CO), 149.13, 146.09, 143.18, 141.62, 140.18, 138.67,
136.05, 132.97, 131.98, 131.50, 130.73, 128.69, 126.83,
123.37, 122.42, 121.87, 120.43, 118.38, 104.53, 93.22
(acetylenic C), 89.74 (acetylenic C), 82.42 (acetylenic C),
81.40 (acetylenic C), 62.34 (80a-C), 59.43 (spiro-C), 53.48
(30-CH3), 51.46 (20-CH3), 22.40 (60-CH3), 21.34 (80a-CH3)
ppm; IR (KBr): ꢀm = 3,089–3,023 (C–H, arom.), 2,898–
2,983 (C–H, aliph.), 2,152 (acetylenic bonds), 1,743
(30-C=O), 1,689 (20-C=O), 1,571 (C=N), 1,473 (C=C),
1,355, 1,253, 1,142, 1,067, 962, 885, 764 cm-1; MS:
m/z = 638.22 [M?].
146.37, 142.85, 141.11, 140.23, 138.47, 136.08, 132.87,
131.50, 130.76, 128.64, 126.64, 123.37, 122.54, 121.97,
120.30, 118.57, 104.36, 93.04 (acetylenic C), 89.53
(acetylenic C), 82.38 (acetylenic C), 81.37 (acetylenic C),
62.28 (80a-C), 59.37 (spiro-C), 53.46 (30-CH3), 51.74 (20-
ꢀ
CH3), 13.79 (Si(CH3)3) ppm; IR (KBr): m = 3,098–3,029
(C–H, arom.), 2,890–2,978 (C–H, aliph.), 2,155 (acetylenic
bonds), 1,745 (30-C=O), 1,689 (20-C=O), 1,580 (C=N),
1,441 (C=C), 1,356, 1,257, 1,178, 1,064, 950, 887,
751 cm-1; MS: m/z = 582.20 [M?].
Dimethyl 2-[[4-[[4-[(trimethylsilyl)ethynyl]phenyl]ethynyl]-
phenyl]ethynyl]spiro[9H-fluorene-9,50(40aH)-pyrrolo[1,2-
b]pyridazine]-60,70-dicarboxylate (13c, C44H34N2O4Si)
Dimethyl 2-[(trimethylsilyl)ethynyl]spiro[9H-fluorene-
9,50(40aH)-pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate
(13a, C28H26N2O4Si)
1
Yield 61%, m.p.: 163 °C; H NMR (400 MHz, CDCl3):
1
Yield 55%, m.p.: 121 °C; H NMR (400 MHz, CDCl3):
d = 7.84–7.87 (d, J = 2.4 Hz, 1H, CH arom.), 7.81–7.84
(d, J = 2.4 Hz, 1H, CH arom.), 7.70–7.74 (d, J = 1.89 Hz,
1H, CH arom.), 7.51–7.54 (m, 6H, CH arom.), 7.46–7.49
(d, J = 7.98 Hz, 2H, CH arom.), 7.43–7.45 (d, J = 2.4 Hz,
1H, CH arom.), 7.40–7.42 (d, J = 2.4 Hz, 1H, CH arom.),
7.35–7.37 (dd, J = 1.76 Hz, J = 1.98 Hz, 1H, 60-CH),
7.32–7.35 (dt, J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.),
7.26–7.28 (dt, J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.),
5.70–5.73 (m, 1H, 70-CH), 4.98–5.01 (t, J = 2.2 Hz, 1H,
80a-CH), 4.73–4.75 (dt, J = 9.60 Hz, J = 1.76 Hz, 80-CH),
3.80 (s, 3H, 30-CH3), 3.45 (s, 3H, 20-CH3), 0.89 (s, 9H,
Si(CH3)3) ppm; 13C NMR (100 MHz, CDCl3): d = 163.45
(30-CO), 161.88 (20-CO), 149.12, 146.34, 143.18, 141.57,
140.20, 138.76, 136.08, 132.79, 131.35, 131.50, 130.76,
128.58, 126.84, 123.36, 122.47, 121.87, 120.36, 118.34,
104.53, 93.64 (acetylenic C), 89.76 (acetylenic C), 82.23
(acetylenic C), 81.10 (acetylenic C), 62.27 (80a-C), 59.31
(spiro-C), 53.47 (30-CH3), 51.52 (20-CH3), 13.81
d = 7.87–7.90 (d, J = 2.4 Hz, 1H, CH arom.), 7.83–7.86
(d, J = 2.4 Hz, 1H, CH arom.), 7.73–7.75 (d, J = 1.89 Hz,
1H, CH arom.), 7.44–7.46 (d, J = 2.4 Hz, 1H, CH arom.),
7.40–7.43 (d, J = 2.4 Hz, 1H, CH arom.), 7.36–7.39 (dd,
J = 1.76 Hz, J = 1.98 Hz, 1H, 60-CH), 7.32–7.35 (dt,
J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.), 7.18–7.22
(dt, J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.), 5.69–5.72
(m, 1H, 70-CH), 4.94–4.96 (t, J = 2.2 Hz, 1H, 80a-CH),
4.70–4.73 (dt, J = 9.60 Hz, J = 1.76 Hz, 80-CH), 3.86 (s,
3H, 30-CH3), 3.47 (s, 3H, 20-CH3), 0.94 (s, 9H, Si(CH3)3)
13
ppm; C NMR (100 MHz, CDCl3): d = 163.37 (30-CO),
161.85 (20-CO), 149.20, 146.36, 142.87, 141.26, 140.37,
138.47, 136.36, 132.90, 130.97, 128.64, 126.78, 123.32,
122.43, 121.58, 120.36, 118.21, 104.78, 82.37 (acetylenic
C), 81.30 (acetylenic C), 62.46 (80a-C), 59.57 (spiro-C),
53.30 (30-CH3), 51.27 (20-CH3), 13.85 (Si(CH3)3) ppm; IR
ꢀ
(KBr): m = 3,098–3,028 (C–H, arom.), 2,880–2,987 (C–H,
aliph.), 2,149 (acetylenic bond), 1,745 (30-C=O), 1,689 (20-
C=O), 1,578 (C=N), 1,424 (C=C), 1,363, 1,254, 1,182,
1,036, 964, 870, 767 cm-1; MS: m/z = 482.17 [M?].
(Si(CH3)3) ppm; IR (KBr): m = 3,087–3,021 (C–H, arom.),
ꢀ
2,894–2,978 (C–H, aliph.), 2,152 (acetylenic bonds), 1,745
(30-C=O), 1,691 (20-C=O), 1,573 (C=N), 1,477 (C=C),
1,352, 1,254, 1,122, 1,046, 960, 877, 763 cm-1; MS:
m/z = 682.23 [M?].
Dimethyl 2-[[4-[(trimethylsilyl)ethynyl]phenyl]ethynyl]-
spiro[9H-fluorene-9,50(40aH)-pyrrolo[1,2-b]pyridazine]-
60,70-dicarboxylate (13b, C36H30N2O4Si)
Dimethyl (40aS)-20,40a-dimethyl-2-[(trimethylsilyl)ethy-
nyl]spiro[9H-fluorene-9,50(40aH)-pyrrolo[1,2-b]pyrida-
zine]-60,70-dicarboxylate (13d, C30H30N2O4Si)
1
Yield 58%, m.p.: 149 °C; H NMR (400 MHz, CDCl3):
d = 7.95–7.98 (d, J = 2.4 Hz, 1H, CH arom.), 7.88–7.90
(d, J = 2.4 Hz, 1H, CH arom.), 7.77–7.79 (d, J = 1.89 Hz,
1H, CH arom.), 7.52–7.55 (d, J = 7.98 Hz, 2H, CH arom.),
7.49–7.51 (d, J = 7.98 Hz, 2H, CH arom.), 7.44–7.46 (d,
J = 2.4 Hz, 1H, CH arom.), 7.43–7.45 (d, J = 2.4 Hz, 1H,
CH arom.), 7.38–7.42 (dd, J = 1.76 Hz, J = 1.98 Hz, 1H,
60-CH), 7.31–7.34 (dt, J = 2.4 Hz, J = 0.88 Hz, 1H, CH
arom.), 7.20–7.24 (dt, J = 2.4 Hz, J = 0.88 Hz, 1H, CH
arom.), 5.76–5.79 (m, 1H, 70-CH), 4.93–4.96 (t,
J = 2.2 Hz, 1H, 80a-CH), 4.68–4.72 (dt, J = 9.60 Hz,
J = 1.76 Hz, 80-CH), 3.81 (s, 3H, 30-CH3), 3.46 (s, 3H, 20-
CH3), 0.91 (s, 9H, Si(CH3)3) ppm; 13C NMR (100 MHz,
CDCl3): d = 163.65 (30-CO), 161.68 (20-CO), 149.20,
1
Yield 67%, m.p.: 112 °C; H NMR (400 MHz, CDCl3):
d = 7.96–7.99 (d, J = 2.4 Hz, 1H, CH arom.), 7.88–7.92
(d, J = 2.4 Hz, 1H, CH arom.), 7.76–7.78 (d, J = 1.89 Hz,
1H, CH arom.), 7.54–7.53 (d, J = 2.4 Hz, 1H, CH arom.),
7.44–7.47 (d, J = 2.4 Hz, 1H, CH arom.), 7.39–7.42 (dt,
J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.), 7.20–7.24 (dt,
J = 2.4 Hz, J = 0.88 Hz, 1H, CH arom.), 5.72–5.74 (m,
1H, 70-CH), 4.80–4.83 (dt, J = 9.60 Hz, J = 1.76 Hz, 80-
CH), 3.84 (s, 3H, 30-CH3), 3.44 (s, 3H, 20-CH3), 2.11 (s,
3H, 60-CH3), 1.43 (s, 3H, 80a-CH3), 0.90 (s, 9H, Si(CH3)3)
13
ppm; C NMR (100 MHz, CDCl3): d = 163.89 (30-CO),
161.94 (20-CO), 149.30, 146.21, 143.85, 141.63, 140.27,
123

Photochromism of dihydroindolizines
369
138.26, 136.33, 133.09, 130.57, 128.42, 126.61, 123.46,
122.60, 121.74, 120.39, 118.46, 104.57, 82.41 (acetylenic
C), 81.22 (acetylenic C), 63.32 (80a-C), 59.21 (spiro-C),
53.46 (30-CH3), 51.23 (20-CH3), 22.41 (60-CH3), 21.28 (80-
3.44 (s, 3H, 20-CH3), 2.13 (s, 3H, 60-CH3), 1.42 (s, 3H,
80a-CH3), 0.86 (s, 9H, Si(CH3)3) ppm; 13C NMR
(100 MHz, CDCl3): d = 163.46 (30-CO), 161.72 (20-CO),
149.27, 146.16, 143.36, 141.84, 140.28, 138.60, 136.16,
133.13, 131.85, 131.49, 130.73, 128.67, 126.75, 123.32,
122.40, 121.79, 120.52, 118.46, 104.79, 93.29 (acetylenic C),
89.58 (acetylenic C), 82.46 (acetylenic C), 81.42 (acety-
lenic C), 62.79 (80a-C), 59.41 (spiro-C), 53.36 (30-CH3),
51.54 (20-CH3), 22.28 (60-CH3), 21.34 (80a-CH3), 13.81
ꢀ
CH3), 13.86 (Si(CH3)3) ppm; IR (KBr): m = 3,098–3,008
(C–H, arom.), 2,842–2,976 (C–H, aliph.), 2,165 (acetylenic
bond), 1,745 (30-C=O), 1,685 (20-C=O), 1,581 (C=N),
1,442 (C=C), 1,359, 1,257, 1,178, 1,081, 958, 877,
763 cm-1; MS: m/z = 510.20 [M?].
ꢀ
(Si(CH3)3) ppm; IR (KBr): m = 3,085–3,013 (C–H, arom.),
Dimethyl (40aS)-20,40a-dimethyl-2-[[4-[(trimethylsilyl)-
ethynyl]phenyl]ethynyl]spiro[9H-fluorene-9,50(40aH)-pyr-
rolo[1,2-b]pyridazine]-60,70-dicarboxylate
(13e, C38H34N2O4Si)
2,898–2,967 (C–H, aliph.), 2,145 (acetylenic bonds), 1,746
(30-C=O), 1,678 (20-C=O), 1,564 (C=N), 1,458 (C=C), 1,351,
1,247, 1,136, 1,067, 960, 879, 763 cm-1; MS: m/z = 710.26
[M?].
1
Yield 64%, m.p.: 125 °C; H NMR (400 MHz, CDCl3):
d = 7.84–7.86 (d, J = 2.4 Hz, 1H, CH arom.), 7.80–7.83
(d, J = 2.4 Hz, 1H, CH arom.), 7.75–7.79 (d, J = 1.89 Hz,
1H, CH arom.), 7.52–7.55 (d, J = 7.98 Hz, 2H, CH arom.),
7.48–7.51 (d, J = 7.98 Hz, 2H, CH arom.), 7.40–7.44 (d,
J = 2.4 Hz, 1H, CH arom.), 7.36–7.39 (d, J = 2.4 Hz, 1H,
CH arom.), 7.32–7.37 (dt, J = 2.4 Hz, J = 0.88 Hz,
1H, CH arom.), 7.21–7.23 (dt, J = 2.4 Hz, J = 0.88 Hz,
1H, CH arom.), 5.69–5.74 (m, 1H, 70-CH), 4.71–4.74 (dt,
J = 9.60 Hz, J = 1.76 Hz, 80-CH), 3.84 (s, 3H, 30-CH3),
3.42 (s, 3H, 20-CH3), 2.11 (s, 3H, 60-CH3), 1.47 (s, 3H, 80a-
CH3), 0.87 (s, 9H, Si(CH3)3) ppm; 13C NMR (100 MHz,
CDCl3): d = 163.46 (30-CO), 161.87 (20-CO), 149.32,
146.28, 143.46, 141.78, 140.36, 138.41, 136.10, 132.74,
131.68, 130.26, 128.64, 126.77, 123.26, 122.47, 121.82,
120.27, 118.46, 104.48, 93.11 (acetylenic C), 89.54
(acetylenic C), 82.47 (acetylenic C), 81.36 (acetylenic C),
62.29 (80a-C), 59.37 (spiro-C), 53.28 (30-CH3), 51.47 (20-
CH3), 22.46 (60-CH3), 21.31 (80a-CH3), 13.78 (Si(CH3)3)
General procedure for the synthesis of photochromic
DHIs–tripodal linker 17b, 17c, 17e, and 17f
Method A. To an oven-dried screw-cap tube or a round-
bottomed flask equipped with a water cooled West con-
denser and a magnetic stir bar the 2-iodosubstituted
fluorene DHIs 11b, 11c, 11e, and 11f (3 mmol), 20 mg
palladium di(triphenylphosphine) dichloride (0.06 mmol),
78 mg triphenylphosphine (0.03 mmol), and 36 mg CuI
(0.15 mmol) were added to 1-(4-iodophenyl)-3,5,7-tris[4-
(ethoxycarbonyl)phenyl]adamantane 15 (3 mmol). The
vessel was then sealed with a rubber septum, evacuated,
and backfilled with nitrogen (three times). A co-solvent
system of 20 cm3 freshly distilled THF and 0.83 cm3 tri-
ethylamine (6 mmol) was added. The reaction mixture was
stirred in an oil bath at 45 °C for 15 h (TLC monitored)
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 (20 cm3). The
organic layer was diluted with CH2Cl2 and washed with a
saturated solution of NH4Cl (3 9 30 cm3). The combined
aqueous layers were extracted with CH2Cl2 (3 9 30 cm3),
dried over anhydrous MgSO4, and the solvent removed in
vacuo. The crude products were then purified by twice
repeated column chromatography on silica gel using
CH2Cl2 as eluent. The pure products were obtained as
yellow needles.
ꢀ
ppm; IR (KBr): m = 3,110–3,043 (C–H, arom.), 2,895–
2,981 (C–H, aliph.), 2,152 (acetylenic bonds), 1,741
(30-C=O), 1,692 (20-C=O), 1,588 (C=N), 1,446 (C=C),
1,375, 1,263, 1,146, 1,087, 955, 896, 761 cm-1; MS:
m/z = 610.23 [M?].
Dimethyl (40aS)-20,40a-dimethyl-2-[[4-[[4-[(trimethyl-
silyl)ethynyl]phenyl]ethynyl]phenyl]ethynyl]spiro[9H-fluo-
rene-9,50(40aH)-pyrrolo[1,2-b]pyridazine]-60,70-dicarbox-
ylate (13f, C46H38N2O4Si)
1
Yield 61%, m.p.: 143 °C; H NMR (400 MHz, CDCl3):
Method B. In comparison with method A 13.5 mg
palladium diacetate (0.06 mmol) was used instead of
20 mg palladium di(triphenylphosphine) dichloride (0.06
mmol) and 20 cm3 toluene and 3 cm3 DMF replaced 20 cm3
THF.
d = 7.98–8.03 (d, J = 2.4 Hz, 1H, CH arom.), 7.92–7.94
(d, J = 2.4 Hz, 1H, CH arom.), 7.81–7.85 (d, J = 1.89 Hz,
1H, CH arom.), 7.50–7.55 (m, 6H, CH arom.), 7.46–7.50
(d, J = 7.98 Hz, 2H, CH arom.), 7.40–7.43 (d, J =
2.4 Hz, 1H, CH arom.), 7.26–7.30 (d, J = 2.4 Hz, 1H,
CH arom.), 7.20–7.24 (dt, J = 2.4 Hz, J = 0.88 Hz, 1H, CH
arom.), 7.16–7.19 (dt, J = 2.4 Hz, J = 0.88 Hz, 1H, CH
arom.), 5.85–5.49 (m, 1H, 70-CH), 4.70–4.74 (dt,
J = 9.60 Hz, J = 1.76 Hz, 80-CH), 3.87 (s, 3H, 30-CH3),
Method C. In comparison with method A 43 mg
bis(dibenzylideneacetone)palladium(0) (0.07 mmol) was
used instead of 20 mg palladium di(triphenylphosphine)
dichloride (0.06 mmol) and 1 cm3 DIEA (6 mmol) replaced
0.83 cm3 triethylamine (6 mmol).
123

370
S. A. Ahmed, S. Y. Al-Raqa
Dimethyl 2-[[4-[3,5,7-tris[4-(ethoxycarbonyl)phenyl]-1-
adamantyl]phenyl]ethynyl]spiro[9H-fluorene-9,50(40aH)-
pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate (17a)
Method A: yield 25%; method B: yield 31%; method C:
yield 54%; analytical data were identical with those
published in Ref. [67].
J = 7.60 Hz, 6H, CH arom.), 7.44–7.48 (d, 10H,
J = 8.72 Hz, CH arom.), 7.33–7.36 (d, 2H, J = 8.69 Hz),
7.15–7.19 (d, 2H, J = 8.60 Hz, CH arom.), 7.12–7.16 (m,
2H, CH arom.), 6.80–6.86 (dd, J = 1.76 Hz, J = 1.76 Hz,
1H, 60-CH), 5.76–5.84 (m, 1H, 70-CH), 5.33–5.37 (t,
J = 2.2 Hz, 1H, 80-CH), 4.96–5.99 (dt, J = 8.00 Hz,
J = 2.00 Hz, 80a-CH), 4.56–4.60 (q, 6H, J = 7.12 Hz,
3CH2 ethyl ester), 3.91 (s, 3H, 30-CH3), 3.43 (s, 3H, 20-
CH3), 2.13 (two overlapping s, 12H), 1.45 (t, 9H,
J = 7.12 Hz, 3CH3 ethyl ester) ppm; 13C NMR
(100 MHz, CDCl3): d = 166.99 (30-CO), 164.36 (20-CO),
162.98 (CO ethyl ester), 153.16, 149.48, 148.37, 148.56,
146.85, 142.69, 141.32, 138.87, 138.36, 138.10, 136.71,
136.63, 133.37, 133.54, 131.36, 130.28, 129.87, 128.71,
127.40, 124.96, 124.37, 123.84, 123.30, 122.11, 121.87,
121.29, 118.64, 116.73, 113.64, 109.52, 94.39 (acetylenic
C), 93.43 (acetylenic C), 89.76 (acetylenic C), 89.32
(acetylenic C), 88.26, 64.64 (80a-C), 63.21 (spiro-C),
61.54, 52.34 (30-CH3), 51.48 (20-CH3), 46.47, 39.63,
30.48, 26.21, 24.60, 23.76, 22.81, 22.13, 14.54,
Dimethyl 2-[[4-[[4-[3,5,7-tris[4-(ethoxycarbonyl)phenyl]-
1-adamantyl]phenyl]ethynyl]phenyl]ethynyl]spiro[9H-flu-
orene-9,50(40aH)-pyrrolo[1,2-b]pyridazine]-60,70-dicarbox-
ylate (17b, C76H64N2O10)
Method A: yield 28%, m.p.: 164 °C; method B: yield 57%,
m.p.: 162 °C; method C: yield 52%, m.p.: 163 °C; 1H NMR
(400 MHz, CDCl3): d = 8.49–8.52 (d, J = 8.00 Hz, 1H,
CH arom.), 8.22–8.42 (d, J = 8.72 Hz, 6H, CH arom.),
8.08–7.12 (d, J = 8.00 Hz, 1H, CH arom.), 7.72–7.75 (d,
J = 7.20 Hz, 1H, CH arom.), 7.53–7.54 (dd, J = 7.20 Hz,
J = 7.60 Hz, 4H, CH arom.), 7.45–7.49 (d, 8H,
J = 8.72 Hz, CH arom.), 7.30–7.35 (d, 2H, J = 8.69 Hz),
7.10–7.14 (d, 2H, J = 8.60 Hz, CH arom.), 7.01–7.10 (m,
2H, CH arom.), 6.84–6.89 (dd, J = 1.76 Hz, J = 1.76 Hz,
1H, 60-CH), 5.69–5.76 (m, 1H, 70-CH), 5.34–5.67 (t,
J = 2.2 Hz, 1H, 80-CH), 4.90–5.94 (dt, J = 8.00 Hz,
J = 2.00 Hz, 80a-CH), 4.53–4.57 (q, 6H, J = 7.12 Hz,
3CH2 ethyl ester), 3.95 (s, 3H, 30-CH3), 3.41 (s, 3H, 20-
CH3), 2.14 (two overlapping s, 12H), 1.41 (t, 9H,
J = 7.12 Hz, 3CH3 ethyl ester) ppm; 13C NMR
(100 MHz, CDCl3): d = 167.46 (30-CO), 165.22 (20-CO),
163.15 (CO ethyl ester), 154.06, 149.68, 148.63, 148.60,
146.98, 142.78, 141.58, 138.97, 138.46, 138.12, 136.85,
136.67, 133.37, 133.25, 131.70, 130.13, 129.82, 128.79,
127.43, 124.79, 124.36, 123.75, 123.36, 122.07, 121.64,
121.38, 118.07, 116.79, 113.63, 109.83, 94.43 (acetylenic
C), 93.45 (acetylenic C), 89.76 (acetylenic C), 89.34
(acetylenic C), 88.36, 64.63 (80a-C), 63.20 (spiro-C),
61.51, 52.36 (30-CH3), 51.46 (20-CH3), 46.48, 39.65,
30.36, 26.20, 24.67, 23.38, 22.84, 22.10, 14.41,
ꢀ
12.17 ppm; IR (KBr): m = 3,089–3,019 (C–H, arom.),
2,890–2,979 (C–H, aliph.), 2,219 (acetylenic bond), 1,743
(30-C=O), 1,708 (CO ester), 1,643 (20-C=O), 1,587 (C=N),
1,449 (C=C), 1,343, 1,252, 1,180, 1,132, 967, 895,
760 cm-1; MS: m/z = 1,264.49 [M?].
Dimethyl (40aS)-20,40a-dimethyl-2-[[4-[3,5,7-tris[4-(eth-
oxycarbonyl)phenyl]-1-adamantyl]phenyl]ethynyl]-
spiro[9H-fluorene-9,50(40aH)-pyrrolo[1,2-b]pyridazine]-
60,70-dicarboxylate (17d)
Method A: yield 22%; method B: yield 34%; method C:
yield 52%; analytical data identical with those published in
Ref. [67].
Dimethyl (40aS)-20,40a-dimethyl-2-[[4-[[4-[3,5,7-tris[4-
(ethoxycarbonyl)phenyl]-1-adamantyl]phenyl]ethynyl]-
phenyl]ethynyl]spiro[9H-fluorene-9,50(40aH)-pyrrolo-
[1,2-b]pyridazine]-60,70-dicarboxylate
ꢀ
12.12 ppm; IR (KBr): m = 3,098–3,032 (C–H, arom.),
(17e, C78H68N2O10)
2,895–2,980 (C–H, aliph.), 2,223 (acetylenic bond), 1,746
(30-C=O), 1,706 (CO ester), 1,646 (20-C=O), 1,584 (C=N),
1,451 (C=C), 1,346, 1,252, 1,181, 1,127, 968, 891,
766 cm-1; MS: m/z = 1,164.46 [M?].
Method A: yield 24%, m.p.: 134 °C; method B: yield 68%,
m.p.: 133 °C; method C: yield 49%, m.p.: 134 °C; 1H
NMR (400 MHz, CDCl3): d = 8.37–8.39 (d, J = 8.04 Hz,
1H, CH arom.), 8.11–8.19 (d, 6H, J = 8.72 Hz), 8.06–8.09
(d, J = 8.00 Hz, 1H, CH arom.), 7.78–7.81 (d,
J = 7.20 Hz, 1H, CH arom.), 7.65–7.66 (dd,
J = 7.20 Hz, J = 7.60 Hz, 4H, CH arom.), 7.55–7.61 (d,
8H, J = 8.72 Hz, CH arom.), 7.42–7.45 (d, 2H,
J = 8.60 Hz), 7.11–7.17 (d, 2H, J = 8.60 Hz), 7.00–7.08
(m, 2H, CH arom.), 5.69–5.73 (m, 1H, 70-CH), 5.13–5.15
(dt, J = 8.00 Hz, J = 2.00 Hz, 80-CH), 4.53–4.56 (q, 6H,
J = 7.12 Hz, 3CH2 ethyl ester), 3.95 (s, 3H, 30-CH3), 3.51
(s, 3H, 20-CH3), 2.17 (two overlapping s, 12H), 2.13 (s, 3H,
60-CH3), 1.60 (s, 3H, 80-CH3), 1.45 (t, 9H, J = 7.12 Hz,
3CH3 ethyl ester) ppm; 13C NMR (100 MHz, CDCl3):
Dimethyl 2-[[4-[[4-[[4-[3,5,7-tris[4-(ethoxycarbonyl)-
phenyl]-1-adamantyl]phenyl]ethynyl]phenyl]ethy-
nyl]phenyl]ethynyl]spiro[9H-fluorene-9,50(40aH)-pyrrol-
o[1,2-b]pyridazine]-60,70-dicarboxylate
(17c, C84H68N2O10)
Method A: yield 27%, m.p.: 143 °C; method B: yield 65%,
m.p.: 141 °C; method C: yield 50%, m.p.: 144 °C; 1H NMR
(400 MHz, CDCl3): d = 8.56–8.59 (d, J = 8.00 Hz, 1H,
CH arom.), 8.32–8.40 (d, J = 8.72 Hz, 6H, CH arom.),
8.11–7.15 (d, J = 8.00 Hz, 1H, CH arom.), 7.70–7.74 (d,
J = 7.20 Hz, 1H, CH arom.), 7.52–7.55 (dd, J = 7.20 Hz,
123

Photochromism of dihydroindolizines
371
d = 167.62 (30-CO), 165.42 (20-CO), 163.36 (CO ethyl
ester), 152.85, 150.33, 148.72, 148.78, 147.54, 142.56,
142.30, 139.68, 138.63, 138.67, 136.14, 136.81, 133.66,
133.47, 131.26, 130.09, 129.79, 128.76, 127.63, 124.46,
124.19, 124.49, 123.36, 122.28, 121.79, 121.53, 118.39,
117.47, 112.49, 105.80, 94.89 (acetylenic C), 93.59
(acetylenic C), 89.98 (acetylenic C), 89.62 (acetylenic C),
88.38, 65.67 (80a-C), 63.45 (spiro-C), 61.81, 52.46 (30-
CH3), 51.27 (20-CH3), 46.95, 39.64, 30.20, 26.37, 24.57,
23.60, 22.23, 22.74 (60-CH3), 22.44, 21.16 (80-CH3), 14.16,
Professor Dr Heinz Du¨rr (University of Saarland, Saarbru¨cken, Ger-
many), Professor Dr Aboel-Magd A. Abdel-Wahab (Assiut
University, Egypt), Henri Bouas-Laurent, and Professor Dr Jean-Luc
Pozzo (University of Bordeaux, France) for their continuous helpful
discussions and carrying out some measurements.
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12.62 ppm; IR (KBr): m = 3,079–3,006 (C–H, arom.),
2,893–2,967 (C–H, aliph.), 2,225 (acetylenic bond), 1,749
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C
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