Photochromism of dihydroindolizines: Part XIV. Synthesis and photophysical behavior of photochromic dihydroindolizine-tripodal linkers toward anchoring sensitizers to semiconductor nanoparticles

Article abstract of DOI:10.1002/poc.1669

Photochromic dihydroindolizines (DHIs) 4a,5-dihydropyrrolo[1,2-b]pyridazine based tripodal-linker systems with adamantane core and ethyl benzoate tripods as anchoring groups have been successfully synthesized. In addition, new spirocyclopropene precursors have been prepared through both chemical and photochemical processes. The photochromic properties of the newly synthesized DHIs derivatives have been optimized and fine-tuned by the incorporation of various substituents on the fluorene (region A) and pyridazine (region C) moieties. Several alternative routes for the synthesis of the DHIs under investigation have been established. The Sonogashira crosscoupling reaction was utilized for fragment coupling between DHIs and the phenylacetylene tether of the adamantane core. Several reaction conditions of this key reaction were surveyed to obtain optimal yields of a new series of coupling products targeted for anchoring to semiconductor nanoparticles. The chemical structures of the newly synthesized materials were elucidated by both analytical and spectroscopic tools. Irradiation of the photochromic DHIs with polychromatic light resulted in ring opened colored betaines which underwent cycloreversion reactions via thermal 1,5-electrocyclization processes. The kinetic of the thermal 1,5-electrocyclization was studied by using a UV/VIS/NIR spectrophotometer. The kinetic measurements showed the half-lives of the colored betaines to be in the second domain. A pronounced increase in the half-lives of betaines bearing dimethyl-substituted pyridazine was noted compared with non-substituted pyridazine betaines. A strong effect of solvent polarity on the λ_max and half-lives of the betaines was observed. The further adjustment of the absorption maxima and the kinetic properties via the manipulation of substituents on the fluorene (region A) and pyridazine moieties (region C) should yield more refined systems for application as supports onto metal-oxide surfaces which remains an active area of our ongoing research. Copyright

Full text of DOI:10.1002/poc.1669

Research Article
Received: 9 June 2009,
Revised: 21 November 2009,
Accepted: 24 November 2009,
Published online 30 March 2010 in Wiley Online Library: 2011
(wileyonlinelibrary.com) DOI 10.1002/poc.1669
Photochromism of dihydroindolizines:
part XIV. Synthesis and photophysical
behavior of photochromic dihydroindolizine-
tripodal linkers toward anchoring sensitizers
to semiconductor nanoparticles
a
b
*
Saleh Abdel-Mgeed Ahmed and Shaya Y. Al-Raqa
Photochromic dihydroindolizines (DHIs) 4a,5-dihydropyrrolo[1,2-b]pyridazine based tripodal-linker systems with
adamantane core and ethyl benzoate tripods as anchoring groups have been successfully synthesized. In addition,
new spirocyclopropene precursors have been prepared through both chemical and photochemical processes. The
photochromic properties of the newly synthesized DHIs derivatives have been optimized and fine-tuned by the
incorporation of various substituents on the fluorene (region A) and pyridazine (region C) moieties. Several alternative
routes for the synthesis of the DHIs under investigation have been established. The Sonogashira crosscoupling
reaction was utilized for fragment coupling between DHIs and the phenylacetylene tether of the adamantane core.
Several reaction conditions of this key reaction were surveyed to obtain optimal yields of a new series of coupling
products targeted for anchoring to semiconductor nanoparticles. The chemical structures of the newly synthesized
materials were elucidated by both analytical and spectroscopic tools. Irradiation of the photochromic DHIs with
polychromatic light resulted in ring opened colored betaines which underwent cycloreversion reactions via thermal
1,5-electrocyclization processes. The kinetic of the thermal 1,5-electrocyclization was studied by using a UV/VIS/NIR
spectrophotometer. The kinetic measurements showed the half-lives of the colored betaines to be in the second
domain. A pronounced increase in the half-lives of betaines bearing dimethyl-substituted pyridazine was noted
compared with non-substituted pyridazine betaines. A strong effect of solvent polarity on the lmax and half-lives of
the betaines was observed. The further adjustment of the absorption maxima and the kinetic properties via the
manipulation of substituents on the fluorene (region A) and pyridazine moieties (region C) should yield more refined
systems for application as supports onto metal-oxide surfaces which remains an active area of our ongoing research.
Copyright ß 2010 John Wiley & Sons, Ltd.
Supporting information may be found in the online version of this paper.
Keywords: anchoring groups; dihydroindolizines (DHIs); photochromism; photofatigue; Sonogashira coupling; tripodal linker
chromenes, azo compounds, and dihydroindolizines (DHIs).
INTRODUCTION
These photochromic families are appealing since they might
find utility in electronic storage media as well as in optoelectronic
devices.[11–13]
Several mandatory properties must be met for the organic
photochromic compounds in order to be useful in photonic
device applications such as erasable memory media and optical
The term photochromism derives from the Greek words ‘‘phos’’
(light) and ‘‘chroma’’ (color) and means the generation of color
under the influence of light. When applied to the molecular
world, this term implies a reversible photoinduced coloration of
an ensemble of molecules in an amorphous, crystalline, or
solution state.[1–7] It is well known that photochromic compounds
support their activities in a reversible photochemical reaction
induced by the absorption of electromagnetic radiation, mainly
in the ultraviolet region to provoke a visible color change of the
original colorless molecule. Throughout the last decade,
photochromic compounds have been included in the develop-
ment process of optoelectronic devices as integral active
components.[8–10] An important characteristic of this optical
change is the clear difference in the absorption spectra shown by
these two species (colored and colorless forms). There exist
several families of compounds that exhibit photochromism such
as diarylethenes, spiropyrans, spirooxazines, fulgides, viologens,
*
Correspondence to: S. A. Ahmed. Present address: Chemistry Department,
Faculty of Science, Taibah University, 30002, Al-Madena Al-Mounawara, Saudi
Arabia.
E-mail: saleh_63@hotmail.com
a
S. A. Ahmed
Department of Chemistry, Faculty of Science, Assiut University, Assiut 71516,
Egypt
b
Shaya. Y. Al-Raqa
Department of Chemistry, Faculty of Science, Taibah University, Al-Madena
Al-Mounawara 30002, Saudi Arabia.
J. Phys. Org. Chem. 2011, 24 173–184
Copyright ß 2010 John Wiley & Sons, Ltd.

S. A.-M. AHMED AND S. Y. AL-RAQA
switching. Foremost are thermal irreversibility, photofatigue
resistance, and high efficiency in rapid photoconversion
processes.[1–7] An additional 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 accomplished by designing photochromic com-
pounds that possess many different locations on their molecular
skeletons where functional groups can be anchored.[14,15] More-
over, p-aggregation of the attached chromophores is a known
problem that changes or even suppresses the chromophore
properties.[16,17] Recently, Tour,[18–24] Galoppini,[25–35] Ru¨ck- Braun,[36]
and others[37–46] have developed three-dimensional linkers with
tetrahedral core unit for sufficient control of the perpendicular shape
and the head group to surface distance of the metal oxide
nanoparticles. Additionally, it has been shown that tripods are
feasible linkers that prevent p-stacking or dimerization of
azobenzenes when adsorbed on gold or applied as AFM-tip.[36–46]
Photochromic DHIs which were discovered and developed by
Du¨rr[47–57] are well-known photochromic materials that have
been attracting much interest from the viewpoint of both
fundamental elucidation of electrocyclization reactions and their
potential applications to optical memories and switches.[58–73]
This class of thermally reversible photochromic switches has
been found to display excellent photochromic properties in
solution as well as in the solid state: excellent fatigue resistance,
short response time, high quantum yields, and large changes of
absorption wavelength between the two isomers. This photo-
chromic family which is based on the 1,5-electrocyclization
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.[74,75] Recently
we have synthesized some new photochromic DHIs bearing
various acetylenic bridges in the fluorene part (region A of the
DHI skeleton) under Sonogashira coupling conditions which may
be useful in the application of electronic devices. In continuation
of our research work dealing with the synthesis and photo-
chromic behavior of photochromic DHIs, in this paper, we
modified the DHI skeleton by substitution in 2- and 7-positions of
the fluorene part (region A) with mono- and di-tripodal linker
unit(s) which may be promising candidates toward anchoring
onto metal oxide nanoparticles. Also, we reported the synthesis
and photophysical properties of a tripodal-linker system with
adamantane core and ethyl benzoate tripods as anchoring
groups and photochromic DHIs bearing variously substituted
pyridazines. Different synthetic outlines of palladium-mediated
Sonogashira coupling will be described.
enones 4a,b as yellow solids in moderate yield (65 and 72% yield,
respectively).
When hydrazine hydrate was allowed to react with substituted
fluorenone derivatives 4a,b in boiling ethanol for 4 h, the
corresponding hydrazones 5a,b were obtained as white crystals
in 82 and 89% yield, respectively. The hydrazone derivatives 5a,b
underwent oxidation with manganese dioxide in dry ether at
room temperature in the absence of light to afford 9-diazo-
2-iodo-9H-fluorene (6a) and 9-diazo-2,7-diiodo-9H-fluorene (6b)
as red needles in moderate yield (56 and 67% yield, respectively).
Cycloaddition of methyl acetylenedicarboxylate (MADC) to the
9-diazofluorene derivatives 6a,b in dry ether under dark
conditions for 12 h led to the formation of dimethyl 2-iodospiro-
[fluorene-9,30-pyrazole]-40,50-dicarboxylate (7a) in 46% yield and
dimethyl 2,7-diiodospiro[fluorene-9,30-pyrazole]-40,50-dicarboxylate
(7b) in 52% yield as pale yellow crystals.
Photolysis of the pyrazole derivatives 7a,b under inert atmos-
phere in dry ether solution for 3 h gave the target spirocyclo-
propene derivatives dimethyl 20-iodospiro[cycloprop[2]ene-1,90-
fluorene]-2,3-dicarboxylate (8a) and dimethyl 20,70-diiodoospiro-
[cycloprop[2]ene-1,90-fluorene]-2,3-dicarboxylate (8b) in 32 and
46% yield, respectively. The chemical structures of the newly
synthesized compounds 2a,b–8a,b (Scheme 1) were confirmed
and established by both spectroscopic (NMR, IR, and mass
spectrometry) and analytical tools (all compounds gave
satisfactory elemental analysis data). For example, the 1HNMR
(400 MHz, CDCl3) of the spirocyclopropene precursor 8b showed
the following signals: d 7.90–7.93 (d, J ¼ 1.76 Hz, 2H, CH-arom.),
7.78–7.79 (d, J ¼ 1.32 Hz, 2H, CH-arom.), 7.62–7.64 (d, J ¼ 8.9 Hz,
2H, CH-arom.); 3.82 (s, 6H, 20, 30-CH3) ppm.
Synthesis of photochromic dihydroindolizines DHIs
11e–h bearing mono- and diiodofluorene (region A)
and substituted pyridazines 9a,b in the heterocyclic
region (region B)
The synthesis of photochromic DHIs, namely, dimethyl-2,7-dibromo-
4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b](substituted)pyridazine]-60,70-
dicarboxylate 11a–d via nucleophilic addition of substituted
pyridazines 9a,b to spirocyclopropenes 1a,b was previously
[70–74]
reported by us
. Likewise, nucleophilic addition of
substituted pyridazines 9a,b to spirocyclopropenes 8a,b[47–75]
(Scheme 2) in dry ether at room temperature and under dry
nitrogen and dark conditions (TLC-monitored using CH2Cl2 as an
eluent) led to the formation of the photochromic DHIs 11e–h in
low to moderate yields (32–56%). The reaction involves the
electrophilic addition of the electron-deficient spirocyclopro-
penes 8a,b to the nitrogen of the N-heterocyclic pyridazines 9a,b
which leads to ring opening via the intermediacy of a
cyclopropyl-allyl conversion of 10e–h to the colored betaines
10e–h (Scheme 2). A subsequent ring closure to DHIs 11e–h
results in a partially slow thermal 1,5-electrocyclization back
reaction (Scheme 2) which can be reversed upon exposure to light.
DHIs 11e–h were obtained in pure form by column chromatog-
raphy on silica gel using dichloromethane as an eluent.
RESULTS AND DISCUSSION
Synthesis of mono- and dihalo-substituted
spirocyclopropene precursors
The mono- and diiodo-substituted spirocyclopropenes 8a and 8b
were prepared in six steps, starting with the precedented
conversion of 2-nitro-9H-fluoren-9-one (2a) and 2,7-dinitro-9H-
fluoren-9-one (2b) to the corresponding 2-amino-9H-fluoren-
9-one 3a and 2,7-diamino 9H-fluoren-9-one 3b by reduction with
stannous chloride in ethyl acetate (Scheme 1).[76,77] Treatment of
compounds 3a,b with sodium nitrite in concentrated sulfuric acid
yielded the corresponding mono- and bis-diazonium salt, which
upon treatment with potassium iodide gave the diiodoflour-
Palladium-mediated Sonogashira coupling of photochromic
DHIs 11a–f tripodal-linker 12 under different reaction
conditions
The synthesis of the tripodal-linker system 12 was carried out
according to well-known literature procedures.[36,78,79] In the
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PHOTOCHROMIC DIHYDROINDOZILINE: TOWARD NANOTECHNOLOGY APPLICATIONS
Scheme 1. Preparation of mono- and diiodo-substituted spirocyclopropenes 8a,b
reaction of bromo-substituted DHIs 11a–d with one or two moles
of the tripodal-linker 12 under standard Sonogashira conditions
(3% Pd(PPh3)Cl2, 10% PPh3, 5% Cu2I2/ Et3N, THF, 18h at 458C,
method A), low yields of coupling products 14a–d were obtained
(10–18% yield, method A; Scheme 3). Changing the reaction
conditions of the Sonogashira coupling by using Pd(OAc)2/PPh3
and 10% Cu2I2, Et3N, toluene, DMF, 24h at 408C (method B)
afforded the coupling products 14a–d in slightly better yields
(14–22%). Aiming to improve the chemical yields of DHIs 14a–d,
the reaction conditions were modified by using bis(dibenzylidene-
acetone)palladium (0) as a Pd(0) source, 10% Cu2I2, triphenylpho-
sphine, DIEA in THF at 408C for 6 h (method C). Such conditions
afforded the coupling products 14a–d in 18–25% yields. In
addition, coupling of photochromic DHIs 11a–d with one or
two moles of the linker 12 using 1,0-phenanthroline NaI, Cu2I2,
DMF, and TEA at 110 8C (method D) did not show any improvement
in the yields of 14a–d and instead resulted in extensive
decomposition. This suggests that the instability of the DHI
system is due to high reaction temperatures and basic reaction
conditions.[74,75]
On the other hand, the coupling reactions of DHIs 11a–d and
the linker 12 using Pd(PPh3)4 in dry pyrrolidine at 50 8C for 6 h
(also RT and 40 8C were done) showed no evidence for the
formation the coupling products 14a–d (method E). In this
method, copper-free reaction conditions were applied to avoid
the homo-dimerization of the linker system. Attempts to improve
the yield by increasing and decreasing the percentage of the
palladium catalyst and the reaction time were unsuccessful in
improving the yields in all of the preceding reactions.
conditions, the mono- and diiodo-substituted DHIs 11e–h
(Scheme 3) were synthesized. The DHIs 11e–h were allowed
to react with the linker 12 under Sonogashira coupling conditions
aiming to get better coupling product yields. The above-
mentioned reaction conditions have been applied during the
reaction of DHI 11e–h with one or two moles of the linker 12 in
order to improve the product yield of the coupling products
14a–d. The best reaction conditions with optimized yields were
found to be with bis(dibenzylideneacetone)palladium (0), Cu2I2,
triphenylphosphine, DIEA in THF at 40 8C for 6 h (method C) which
led to the formation of the coupling products 14a–d in 52–69%
yield. All of the preceding various coupling conditions (Methods
A–E) for the synthesis of DHIs 14a–d were applied to mono- and
diiodo-substituted DHIs 11e–h and the yields were measured
(Method A, 22–29%; Method B, 30–37%; Method D, 7–10%, and
Method E, 9–12%). Pronounced improvements in reaction yields
using mono- and diiodo-substituted DHIs 11e–h compared with
mono- and dibromo-substituted DHIs 11a–d were noted. The
yields of DHIs 14a–d using the reaction conditions of methods D
and E were still low, albeit better than those obtained in the
coupling reactions with DHIs 11a–d bearing mono- and
dibromo-substituted DHIs using the same methods. The chemical
structures of all newly synthesized photochromic DHIs 14a–d
were established on the basis of spectral and analytical tools as
they showed spectral data corroborating the suggested chemical
structures and also gave the satisfactory elemental analyses data.
For instance, assignments of 80-CH, 80a-CH as well as some other
diagnostic protons in the DHI skeleton were done by the aid of
NOESY spectrum of 14c. Herein, we observed that 80a-CH at
d ¼ 4.83 ppm is close in space to 80-CH at d ¼ 5.07 ppm, and 1-CH
of the fluorene moiety at d ¼ 7.63 ppm. This shows that 80a-CH is
In order to increase the reactivity of DHIs 11a–d toward the
coupling with the tripod 12 under Sonogashira coupling
J. Phys. Org. Chem. 2011, 24 173–184
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S. A.-M. AHMED AND S. Y. AL-RAQA
—
—
—
—
—
—
—
H; 11f, R
—
1
Scheme 2. Structures of known DHIs 11a–d and synthetic outline to the new photochromic dihydroindolizines 11e–h (11e, R1
R
2
X
—
—
—
—
—
—
—
—
—
—
CH , X I)
—
3
—
R2 CH , X H; 11g, R
R
2
H, X I; 11h, R
—
R
—
—
—
3
1
1
2
in 8‘a-position and not at 8‘-position. Indeed, the connectivity
between 80-CH and 8-CH of the fluorene part at d ¼ 7.54 ppm was
observed. This close proximity of 80-CH with 8-CH suggests that
the pyridazine moiety is perpendicular to the fluorene skeleton.
This observation is also supported by molecular modeling calcu-
lation of DHI 14a (Fig. 1). The molecular mechanics calculation
(MM2) showed t0hat the distance between both 80a-CH and 80-CH
obtained from the absorption features of photochromic DHIs
11e–h and 14a–d. Electronic spectra of the newly synthesized
DHIs 11e–h and 14a–d were measured in dichloromethane using
a
UV/VIS/NIR spectrophotometer with a concentration of
1 ꢀ 10ꢁ5 mol/L at 23 8C. All of the studied DHIs 11e–h and
14a–d are yellow in the solid state and in dichloromethane
solution (Table 1). The intensities (log e) of the absorption bands
ranged between 3.96 and 4.49 depending on whether the
fluorene is substituted by one or two iodine atoms (DHIs 11e–h)
as well as one or two tripodal units (DHIs 14a–d). The absorption
of DHIs 11e–h and 14a–d were observed in the far UV-region and
showed maxima lying between 393 and 407 nm (Table 1). This
absorption depends on the number of the tripodal units on the
fluorene group (region A). No significant effect on the absorption
of mono- and diiodo-substituted DHIs 11a–d was recorded. A
pronounced bathochromic shift of di-substituted tripodal-DHI
14c,d by about 8 nm compared with mono-substituted tripodal-
DHI was monitored. This may be attributed to the increase in
extended conjugation in the DHI skeleton after the coupling
reaction. Changing the substitution in the pyridazine region from
un-substituted to substitution by two methyl groups could not
˚
connected to 6 -CH and 1-CH of the fluorene moiety is <3 A
which is in good agreement with the NMR results (Fig. 1).
Photophysical properties of the newly synthesized
photochromic DHIs 11e–h and 14a–d and their
corresponding betaines 10e–h and 13a–d in
dichloromethane solution at ambient temperature
Absorption spectra of DHIs 11e–h and 14a–d and their
corresponding betaines 10e–h and 13a–d in solution
The absorption spectra of DHIs 11a–d and their corresponding
betaines 10a–d were previously studied by us.[63–75] Photo-
physical data pertinent to their photochromic properties were
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PHOTOCHROMIC DIHYDROINDOZILINE: TOWARD NANOTECHNOLOGY APPLICATIONS
—
—
— —
Y H; 14b,
Scheme 3. Palladium-mediated Sonogashira coupling of DHIs 11a–h and tripod-linker 12 for the synthesis of DHIs 14a–d (14a, R1
R
2— —
—
—
—
—
—
—
—
—
—
—
—
—
R CH )
—
2
R1
R
2
CH , Y H; 14c, R
R
2
H; 14d, R
—
3
1
1
3
influence the absorption maxima of the DHI system. As
established previously,[47–75] these absorption bands can be
*
assigned to the locally excited p–p -transition (LE) located in the
butadienyl-vinyl-amine chromophores of the DHIs 11e–h and
14a–d (Table 1).
Irradiation of DHIs 11e–h and 14a–d with polychromatic light
led to ring opened betaines (Figs. 2–4). The colored betaine forms
10e–h and 13a–d showed red to blue-green colors in CH2Cl2
solution (with a concentration of 1 ꢀ 10ꢁ5 mol/L) at room tempe-
rature because of their inherent sluggish 1,5-electrocyclization.
The absorption maxima of the colored betaines 10e–h and
13a–d were found in the visible region lying between 520
(betaine 10a) and 639 nm (betaine 13d). The UV-spectra of the
colored betaines containing non-substituted pyridazine as a
heterocyclic moiety in region C as in betaines 10e,g and 13a,c
(Fig. 3) exhibit red colored betaines and showed only one
absorption maximum between 520 and 530 nm. On the other
hand, the betaine forms which contain substituted dimethyl
pyridazine in region C as in the case of betaines 10f–h and 13b,d
(Figs 2 and 4) exhibited green-blue colored betaines and showed
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S. A.-M. AHMED AND S. Y. AL-RAQA
Table 1. UV/VIS/NIR absorption DHIs 11e–h and 14a–d and their corresponding betaines 10e–h and 13a–d and kinetic data of
betaines 10e–h and 13a–d in the second range (recorded by UV/VIS/NIR-spectrophotometer) in CH2Cl2 solution (23 8C,
c ¼ 1 ꢀ 10ꢁ5 mol/L)
DHI/betaine
lmax (DHI) (nm)
log (e)
lmax (betaine) (nm)
k ꢀ 10ꢁ3 (sꢁ1
)
t1/2 (s)
Color of betaine
11e/10e
11f/10f
393
394
396
398
402
403
405
407
3.96
3.98
4.03
4.11
4.22
4.34
4.39
4.49
520
350, 444,627
523
354, 448,629
529
353, 442,632
530
354, 443,635
5.25
0.62
6.13
0.72
2.57
0.46
1.95
0.39
132
1120
113
968
270
1513
356
1769
Red
Blue-green
Red
Blue-green
Red
Blue-green
Red
Blue-green
11g/10g
11h/10h
14a/13a
14b/13b
14c/13c
14d/13d
Figure 1. Representation of the optimized (MM2) structure of DHI 14a.
Figure 2. UV/VIS/NIR of photochromic DHI 14d and the corresponding
betaine form 13d after UV irradiation in CH2Cl2 (c ¼ 1 ꢀ 10ꢁ5 mol/L) at
ambient temperature.
three absorption maxima with three isobestic points (Table 1,
Figs 2 and 4). The existence of the three isobestic points proves
that the thermal back reaction of the colored betaines follows
first order. Interestingly, a bathochromic shift of the absorption of
the betaines containing non-substituted pyridazines 10e,g and
13a,c by more than 110 nm in the visible region compared with
the betaines with dimethyl-substituted pyridazines 10f–h, 13b,d
was recorded. This wide-range bathochromic shift led to the
change of the betaine colors from red to green-blue which can
be attributed to the increase in the electron donating abilities of
the two methyl groups to stabilize the zwitter ionic betaine
forms[70,71,74,75] (Table 1). Furthermore, a noticeable bathochro-
mic shift of about 3–4 nm accompanied the increase in the
number of tripodal units from 1 to 2 which did not show any
dependence on the substituted or non-substituted pyridazine.
This may be attributed to the extended conjugation of the
fluorene unit with the tripodal-acetylenic aromatic phenyl rings
of the tripodal system. Further spectroscopic data related to the
UV/VIS measurements of the colored betaines 10e–h and 13a–d
are listed in Table 1.
The kinetics of the thermal 1,5-electrocyclization was studied
by using a UV/VIS/NIR spectrophotometer (Figs. 3 and 4). The
kinetic measurements showed that the half-lives of the colored
betaines 10e–h and 13a–d are in the second domain and lie
between 113 and 1769 s (Table 1, Figs. 3 and 4). A highly
Figure 3. Kinetic UV/VIS/NIR spectrum of the thermal fading of betaine
10g to DHI 11g (cycle time ¼ 30 s, run time ¼ 400 s) in CH2Cl2 (c ¼ 1 ꢀ
10ꢁ5 mol/L) at 253 K.
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PHOTOCHROMIC DIHYDROINDOZILINE: TOWARD NANOTECHNOLOGY APPLICATIONS
Figure 4. Kinetic UV/VIS/NIR spectrum of the thermal fading of betaine
Figure 6. UV-Bleaching and thermal fading between betaine 13c and
13b to DHI 14b (cycle time ¼ 200 s, run time ¼ 3000 s) in CH2Cl2
DHI 14c and the standard betaine/DHI system (irradiation/thermal fading/
irradiation cycles) with irradiation time of 5 min at wavelength 530 nm in
CH2Cl2 (c ¼ 1 ꢀ 10ꢁ5 mol/L) at ambient temperature.
(c ¼ 1 ꢀ 10ꢁ5 mol/L) at 253 K.
pronounced increase in the half-lives of the betaines bearing
dimethyl-substituted pyridazine 10f, 10h, 13b, and 13d by
approximately a factor of 7 compared with the half-lives of the
betaines bearing non-substituted pyridazine 10e, 10g, 13a, and
13c is noted. This increase in the half-lives may be attributed to
the stabilization of the positive and negative charges on the
betaines forms by the electron-donating methyl groups. An
increase in the half-lives of the betaine forms by increasing the
number of the tripod linker from mono-substituted (13b) to
di-substituted (13d) tripod-DHIs by approximately a factor of 1.30
was observed. Also, a noticeable increase in the half-lives of the
betaines coupled with tripodal molecules as in 13a–d compared
with non-coupled betaines 10e–h by a factor of 1.5–2.0 was
observed. These tunings of the absorption maxima and the
kinetic properties by the changing of the substitution in the
fluorene part (region A) as well as in the pyridazine part (region C)
are important to develop the potential of such compounds
toward applications.
Photo-fatigue resistance of photochromic DHIs 11e–h and 14a–d
and their corresponding betaines 10e–h and 13a–d in
dichloromethane solution (c ¼ 1 ꢀ 10ꢁ5 mol/L) at 253 K
The photostability of the photochromic materials is a very important
property for assessing their quality as suitable for applications. As
such, in a photochromic system, the problem of carrying out a
large number of coloration–decoloration cycles arises frequently.
The gradual loss of the ability to change color by exposure to
visible or ultraviolet light in this context has been termed
Figure 5. Balcony diagram representing the time-relative absorbance
relationship of the photodegradation experiment for determination the
t30-value of the betaines 10e–h and 13a–d in CH2Cl2 (c ¼ 1 ꢀ 10ꢁ5 mol/L)
at ambient temperature.
Figure 7. Influence of solvent polarity on the half-lives (t1/2) of betaines
10e–h and 13a–d monitored by UV/VIS/NIR (c ¼ 1 ꢀ 10ꢁ5 m/L) at 23 8C.
J. Phys. Org. Chem. 2011, 24 173–184
Copyright ß 2010 John Wiley & Sons, Ltd.
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S. A.-M. AHMED AND S. Y. AL-RAQA
Table 2. Photodegradation data of betaines 10e–h and 14a–d in dichloromethane solution (c ¼ 1 ꢀ 10ꢁ5 mol/L) at 23 8C
Betaines
t30-betaine/ DHI (min)
F
Betaines
t30-betaine/ DHI (min)
F
10e
10f
10g
10h
425
649
502
717
243
1.75
2.67
2.07
2.95
1.00
13a
13b
13c
13d
243
583
694
510
628
243
2.40
2.86
2.10
2.58
1.00
Standard
Table 3. Solvatochromic effect on the (t1/2) of thermal 1,5-electrocyclization of selected betaines 10e–h and 13a–d and ET(30)
values of ten different solvents recorded by kinetic UV/VIS/NIR technique (c ¼ 1 ꢀ 10ꢁ5 mol/L) at ambient temperature
Betaines t1/2 (s)
Solvents
10e
10f
10g
10h
13a
13b
13c
14d
ET(30)
n-Pentane
Toluene
Dioxane
Tetrahydrofurane
Chloroform
Dichloromethane
Acetonitrile
2-Propanol
Ethanol
98
882
913
983
1020
1052
1120
1276
1321
1437
1543
79
99
545
801
861
896
929
968
1122
1168
1253
1330
201
229
246
256
267
270
318
342
349
379
1162
1231
1346
1367
1423
1500
1673
1812
1907
2067
278
281
316
328
341
350
386
432
450
486
1351
1418
1526
1543
1640
1722
1924
2079
2195
2341
32
34
36
37
39
41
46
49
52
56
104
103
110
126
132
160
167
176
186
106
107
111
113
132
142
149
162
Methanol
fatigue.[1–7] Gautron[80] has advanced a quantitative approach to
measure the fatigue in photochromic systems.
13a, and 13c by a factor of about 0.2 has been seen. Interestingly,
the tripodal-betaines 13a–d showed higher t30-values compared
with other betaines under investigation. Betaine 13b
(t30 ¼ 694 min) substituted with two methyl groups in the
pyridazine moiety showed the highest photo-fatigue resistance
compared with other betaines 13a,c,d and also by a factor of 1.86
compared with the standard betaine (t30 ¼ 243 min). The high
detectable photostability of these materials will help this family
to find their applications.
Figure 6 represents an interesting property of the UV-bleaching/
thermal fading of the DHI 13c and DHI 14c and the standard
betaine dicyanopyridazine-DHI with irradiation time of 5 min and
waiting for thermal fading for 1 h for 20 cycles (number of cycle
means the bleaching and thermal fading which corresponds to
one cycle). These cycles of DHI/betaine showed after irradiation
and thermal fading no big evidence of any decomposition
compared with the standard betaine product as recorded by the
UV/VIS measurements.
Due to the slow thermal bleaching process of the betaines to
DHIs, a temperature UV/VIS/NIR measurement was used in this case.
Irradiation of the degassed dichloromethane solution of DHIs
11e–h and 14a–d at room temperature (23 8C) with polychromatic
light (l ¼ 200–400nm) led to the formation of the colored betaines
10e–h and 13a–d. Upon continued irradiation they decomposed
after some time (irradiation time means the continuous irradiation
of the colored betaines for a fixed duration of time). However, if
oxygen is excluded, these systems are noticeably more stable. It is
possible that in the presence of oxygen, the betaines 10e–h and
13a–d act as sensitizers toward singlet oxygen.[70,71]
The t30-value is defined as the measure of the decrease in the
initial absorbance by 70% with remaining 30% of the betaines
absorbance at zero time of the photodegradation experiment.
The factor in the photofatigue resistance is the relative value of
the t30-value of the measured compound and the t30-value of the
standard compound (dicyano-pyridazine DHI). From the photo-
stability measurements listed in Fig. 5 and Table 2 it is clear that all
betaines under investigation showed a higher photo-fatigue
resistance than the standard dicyano-pyridazine DHI (t30 ¼ 243 min)
by a factor ranging between 1.75 as in the case of betaine 10e and
2.95 as in the case of betaine 10h. A pronounced increase of the
t30-values by substitution of the fluorene part by mono- and
di-substituted tripod-units was observed. An increase in the
t30-values of the betaines incorporating two methyl pyridazine as
in betaines 10f, 10h, 13b, and 13d compared with the betaines
incorporating non-substituted pyridazine as in betaines 10e, 10g,
Solvatochromism
It has been known that UV/VIS/NIR-absorption spectra of the
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 bands.[81–85] A strong
effect of the solvent polarity on the lmax and half-lives of betaines
10e–h and 13a–d was observed. Changing the solvent from
tetrahydrofurane (ET(30) ¼ 37) to methanol (ET(30) ¼ 56) led to a
hypsochromic shift ranged between Dnffi þ 820 and Dnffi þ
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Copyright ß 2010 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2011, 24 173–184

PHOTOCHROMIC DIHYDROINDOZILINE: TOWARD NANOTECHNOLOGY APPLICATIONS
1198 cmꢁ1 in the absorption in visible region. These two
solvatochromic shifts are ascribable to p–p* transitions in the
visible region.
procedures published by Galoppini[25–35] and Ru¨ck-Braun.[36] Full
characterization of spirocyclopropenes 8e–h will be given in
details in the forthcoming paper.[87] Solutions to be photolyzed
were flushed with dry nitrogen for 30 min before switching on the
UV lamp. Progress of the reaction and purity of the products
isolated were monitored using thin layer chromatography (TLC).
Separation and purification of all synthesized photochromic
materials were carried out using column chromatography (80 cm
length ꢀ 2 cm diameter) on silica gel and CH2Cl2 as an eluent.
Melting points were determined on an Electrothermal Eng. Ltd
melting point apparatus and are uncorrected. Some procedures
are indispensable to obtain high quality analytical results such as
(1) the purifications of the DHIs were done by two or three times
column chromatography till showing NMR highly pure spectra,
(2) the obtained samples after chromatographic purifications
were vacuum dried for 48 h at 45 8C, (3) the samples to be
analyzed were weighed in a moisture free atmosphere, and (4)
the analysis process was repeated for at least three times and the
average values were taken.[88–93] All NMR spectra were collected
on a Bruker DRX 400 spectrometer (400 MHz) in CDCl3 using TMS
as the internal standard. Chemical shifts (d) are reported in ppm.
FT-IR measurements were performed using a Perkin Elmer
Paragon 1000 instrument. Mass spectra were recorded on a VG
AutoSpec apparatus 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 a matrix. IR spectra
were measured on a BIO-Rad Excalibur series, FTS 3000.
UV-spectra were recorded on a UV/VIS/NIR JASCO V-570
computerized spectrophotometer. Experimental details, pro-
cedures, and full characterizations of the new synthesized DHIs
11e–h and 14a–d are described below.
A pronounced solvent influence on the half-lives (t1/2) of the
selected betaines 10e–h and 13a–d was determined using UV/
VIS technique at room temperature in ten different solvents
(Table 3). A pronounced increase in the half-lives with increasing
solvent polarity was recorded in all studied betaines 10e–h and
13a–d (Fig. 7). This is mainly attributed to the partial charge
transfer from the betaine form to the solvent and vice versa, as a
result of weak Coulombic-exchange effects. Therefore, the
charged zwitterionic betaine structure was stabilized by increas-
ing the solvent polarity due to the electrostatic interactions
between them. The strong tuning of the half-lives in the different
media polarities will help these compounds to select the solvent
for suitable applications.
Conclusion
Eight photochromic tripodal-DHI derivatives have been synthes-
ized though multistep reactions. Palladium-mediated Sonoga-
shira coupling reactions have been applied for mono-, di-bromo,
and -iodosubstituted fluorene moieties of the DHI system for
optimized reaction conditions and product yields. The coupling
reactions have been carried out on the fluorene group (region A)
with the flexible tripodal system having anchoring groups to help
the extension of the photochromism of the target molecules for
future applications by supporting them on the surfaces of
metal-oxides nanoparticles. In addition, new mono- and
di-iodosubstituted spirocyclopropenes and their corresponding
DHIs have been synthesized. Different attempts toward optimiz-
ing conditions for the Sonogashira-mediated coupling of the DHI
skeleton with the tripodal system and the adamantane core have
been presented. Interesting photochromic properties with tuning
of the chemical structure of the photochromic DHIs by changing
the substitutions in the fluorene part and in the pyridazine region
have been recorded. This pronounced influence of the
substitutions in both A and C regions showed strong effects
on the UV/VIS absorption of DHIs and betaines as well as on
kinetic properties (half-lives). These newly synthesized photo-
chromic DHIs and their corresponding betaines showed a very
low ability to the photodegradation by direct irradiation or by
cycling between opened and closed forms for 20 cycles. The
solvent effect of ten solvents with different polarities on the
photochromism of DHIs and their corresponding betaines has
been observed. The tuning of the photochromic properties of the
new DHIs and their corresponding betaines will help to find
suitable applications. More studies on the anchoring of these
compounds onto the surface of metal oxides will be discussed in
details in the ongoing research work.
Synthesis of photochromic dihydroindolizines 11e–f:
General procedure
A mixture of spirocyclopropenes 8a,b (1 mmol) in 50 ml dry ether
and pyridazine 8a and 2,6-dimethyl pyridazine (1.5 mmol) was
stirred at room temperature under dry N2 with exclusion of light
for 24 h (TLC-controlled). Ether was removed under reduced
pressure and the residues were purified by column chromatog-
raphy on silica gel and dichloromethane as an eluent. The pure
product was obtained after crystallization from the proper
solvents to afford the products as yellow crystals.
Dimethyl 2-iodo-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-
60,70-dicarboxylate 11e: R1
R
X
H, yield ¼ 45%, mp ¼ 98 8C.
—
— —
—
2— —
1H NMR (400 MHz, CDCl3) d 8.22–8.24 (d, J ¼ 8.00 Hz, 1H,
CH-arom.), 7.93–7.94 (d, J ¼ 8.00 Hz, 1H, CH-arom.), 7.76–7.78
(d, J ¼ 7.20 Hz, 1H, CH-arom.), 7.60–7.66 (dd, J ¼ 7.20, J ¼ 7.60 Hz,
2H, CH-arom.), 7.41–7.48 (m, 2H, CH-arom.), 6.95–6.98 (dd,
J ¼ 1.76, J ¼ 1.76, 1H, 60-CH), 5.64–5.67 (m, 1H, 70-CH), 5.13–5.17 (t,
J ¼ 2.2 Hz, 1H, 80-CH), 4.86–4.98 (dt, J ¼ 8.00 Hz, J ¼ 2.00 Hz,
8a0-CH), 3.84 (s, 3H, 30-CH3), 3.49 (s, 3H, 20-CH3) ppm. 13CNMR
(400 MHz, CDCl3) d 164.25 (30-CO), 162.31 (20-CO), 149.82, 148.85,
142.52, 139.13, 138.62, 138.34, 133.61, 133.37, 130.06, 127.64,
124.16, 123.78, 124.25, 122.01, 121.39, 118.82, 105.86, 65.24
(80a-C), 63.28 (spiro-C), 53.79 (30-CH3), 51.46 (20-CH3) ppm; IR (KBr):
n ¼ 3136ꢁ3097 (C-H, arom.), 2832–2990 (C—H, aliph.), 1740
EXPERIMENTAL
Photolysis of the corresponding pyrazole derivatives 7a,b has
been done in the photochemical reactor of Schenck[86] made
from Pyrex (l > 290 nm) according to reported procedures.[86]
The source of irradiation was a high pressure mercury lamp
Philips-HPK (125 W) and the photolysis time is 3 h. Photochromic
DHIs 11a–d were previously prepared by us.[70,71,74,75] The
tripod-linker system 12 was prepared following the reaction
0
0
—
—
—
—
—
(3 -C O), 1692 (2 -C O), 1584 (C N), 1446 (C C), 1329, 1243,
—
—
—
1182, 1084, 957, 880, 772 cmꢁ1; HR-MS m/e (%) 512.02 [Mþ];
Elemental Analysis for C23H17IN2O4: C, 53.92; H, 3.34; N, 5.47;
Found %: C, 53.93; H, 3.33; N, 5.46.
J. Phys. Org. Chem. 2011, 24 173–184
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S. A.-M. AHMED AND S. Y. AL-RAQA
Dimethyl
2-iodo-20,4a0-dimethyl-4a0H-spiro[fluorene-9,50-
DHIs 11a–h (3 mmol), bis(dibenzylideneacetone)palladium(0)
(86 mg, 0. 15 mmol), copper(I) iodide (72 mg, 0.3 mmol), triphenyl-
phosphine (157 mg, 0.06 mmol) to 1-(ethynylphenyl)-3,5,7- tris(4-
carboethoxy)adamantane 12 (1.49 mmol). The vessel was then
sealed with a rubber septum, evacuated, and backfilled with
nitrogen (three times). A co-solvent system of freshly distilled THF
(20 ml) followed by DIEA (2.1 ml, 12 mmol) were added. The
reaction mixture was stirred in a 40 8C oil bath for 6 h
(TLC-controlled) until the reaction is completed. 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
(3 ꢀ 30 ml). The combined aqueous layers were extracted with
CH2Cl2 (3 ꢀ 30ml). The combined organic layers were dried over
anhydrous MgSO4 and the solvent removed under reduced
pressure. The crude products were then purified by twice column
chromatography on silica gel and CH2Cl2 as an eluent. The pure
products were obtained with highly purity as yellow needles. Full
characterizations of the coupling products 14a–d are cited below:
Dimethyl 2-(ethynylphenyl)-3,5,7-tris(4-carboethoxy)adamantyl-
pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 11f: R1
R
—
—
CH ,
—
—
2
3
X ¼ H, yield ¼ 32%, mp ¼ 72 8C. 1H NMR (400 MHz, CDCl3) d
8.17– 8.20 (d, J ¼ 8.00 Hz, 1H, CH-arom.), 7.90–7.93 (d, J ¼ 8.00 Hz,
1H, CH-arom.), 7.81–7.83 (d, J ¼ 7.20 Hz, 1H, CH-arom.), 7.66–7.69
(dd, J ¼ 7.20, J ¼ 7.60 Hz, 2H, CH-arom.), 7.44–7.50 (m, 2H,
CH-arom.), 5.67–5.92 (d, J ¼ 9.73 Hz, 1H, 70-CH), 5.10–5.13 (d,
J ¼ 9.72 Hz, 1H, 80-CH), 3.87 (s, 3H, 30-CH3), 3.32 (s, 3H, 20-CH3), 2.12
(s, 3H, 60-CH3), 1.54 (s, 3H, 80-CH3) ppm. 13CNMR (400 MHz, CDCl3)
d 164.03 (30-CO), 162.12 (20-CO), 149.23, 147.48, 144.32, 139.75,
138.01, 132.72, 131.43, 131.73, 129.54, 127.73, 121.17, 121.35,
121.08, 119.24, 101.46, 67.23 (80a-C), 66.85 (spiro-C), 53.27
(30-CH3), 51.19 (20-CH3), 22.47 (60-CH3), 21.27 (80-CH3) ppm; IR
(KBr): n ¼ 3121 (C—H, arom.), 2912–2998 (C—H, aliph.), 1740
0
0
—
—
—
—
—
(3 -C O), 1687 (2 -C O), 1615 (C N), 1533 (C C), 1449, 1363,
—
—
—
1278, 1154, 1101, 949, 880, 767 cmꢁ1; HR-MS m/e (%) 540.05 [Mþ];
Elemental Analysis for C25H21IN2O4: C, 55.57; H, 3.92; N, 5.18;
Found %: C, 55.56; H, 3.92; N, 5.17.
Dimethyl
2,7-diiodo-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]
pyridazine]-60,70-dicarboxylate 11g: R1
R
H, X ¼ I, yield ¼
—
—
—
—
2
56%, mp ¼ 127 8C.1H NMR (400 MHz, CDCl3) d 8.34– 8.37 (d,
J ¼ 8.00 Hz, 1H, CH-arom.), 7.95–7.96 (d, J ¼ 8.00 Hz, 1H,
CH-arom.), 7.72–7.74 (d, J ¼ 7.20 Hz, 1H, CH-arom.), 7.53–7.56
(dd, J ¼ 7.20, J ¼ 1.76 Hz, 1H, CH-arom.), 7.47–7.50 (m, 2H,
CH-arom.), 6.95–6.98 (dd, J ¼ 1.76, J ¼ 1.76, 1H, 60-CH),
5.60–5.64 (m, 1H, 70-CH), 5.17–5.20 (t, J ¼ 2.2 Hz, 1H, 80-CH),
4.90–4.93 (dt, J ¼ 8.00 Hz, J ¼ 2.00 Hz, 8a0-CH), 3.81 (s, 3H, 30-CH3),
3.52 (s, 3H, 20-CH3) ppm. 13CNMR (400 MHz, CDCl3) d 164.75
(30-CO), 162.97 (20-CO), 150.12, 148.64, 142.73, 139.64, 138.74,
138.30, 133.94, 133.22, 129.12, 127.87, 124.27, 123.45, 124.78,
121.67, 121.20, 118.87, 105.86, 65.20 (80a-C), 63.35 (spiro-C), 53.87
(30-CH3), 51.57 (20-CH3) ppm; IR (KBr): n ¼ 3101–3087 (C—H, arom.),
4a H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate
0
—
—
—
—
14a: From DHI 11a; R1
R
H, method A, yield ¼ 13%,
2
mp ¼ 137 8C; method B, yield ¼ 12%, mp ¼ 136 8C; method C,
—
—
—
H,
—
yield ¼ 20%, mp ¼ 136–137 8C; from DHI 11e: R1
R
2
method A, yield ¼ 25%, mp ¼ 136 8C; method B, yield ¼ 31%,
mp ¼ 137 8C; method C, yield ¼ 54%, mp ¼ 136 8C; method D,
yield ¼ 8%, mp ¼ 136 8C; method E, yield ¼ 10%, mp ¼ 137 8C. 1H
NMR (400 MHz, CDCl3) d 8.46– 8.49 (d, J ¼ 8.00 Hz, 1H, CH-arom.),
8.15–8.17 (d, 6H, J ¼ 8.72 Hz), 8.08–7.13 (d, J ¼ 8.00 Hz, 1H,
CH-arom.), 7.65–7.68 (d, J ¼ 7.20Hz, 1H, CH-arom.), 7.53–7.54
(dd, J ¼ 7.20, J ¼ 7.60 Hz, 2H, CH-arom.), 7.43–7.47 (d, 6H,
J ¼ 8.72 Hz), 7.36–7.40 (d, 2H, J ¼ 8.60 Hz), 7.16–7.19 (d, 2H,
J ¼ 8.60 Hz), 7.08–7.14 (m, 2H, CH-arom.), 6.92–6.95 (dd, J ¼ 1.76,
J ¼ 1.76, 1H, 60-CH), 5.60–5.62 (m, 1H, 70-CH), 5.20–5.23 (t,
J ¼ 2.2 Hz, 1H, 80-CH), 4.97–5.01(dt, J ¼ 8.00 Hz, J ¼ 2.00 Hz,
8a0-CH), 4.46–4.50 (q, 6H, J ¼ 7.12 Hz), 3.90 (s, 3H, 30-CH3), 3.42
(s, 3H, 20-CH3), 2.16 (two overlapping, s, 12H), 1.42 (t, 9H,
0
0
—
—
—
2898–2982 (C—H, aliph.), 1737 (3 -C O), 1687 (2 -C O), 1580
—
ꢁ1
—
—
(C N), 1441 (C C), 1330, 1241, 1178, 1088, 960, 875, 762 cm
;
—
—
HR-MS m/e (%) 637.92 [Mþ]; Elemental Analysis for C23H16I2N2O4: C,
43.29; H, 2.53; N, 4.39; Found %: C, 43.30; H, 2.54; N, 4.40.
Dimethyl
2,7-diiodo-20,4a0-dimethyl-4a0H-spiro[fluorene-9,50-
13
pyrrolo[1,2-b]pyridazine]-60,70-dicarboxylate 11h: R1
R
J ¼ 7.12 Hz) ppm. CNMR (400 MHz, CDCl3) d 167.25 (30-CO),
—
—
CH ,
—
—
2
3
X ¼ I, yield ¼ 39%, mp ¼ 103 8C.1H NMR (400 MHz, CDCl3) d
8.20–8.23 (d, J ¼ 8.00 Hz, 1H, CH-arom.), 7.96–7.99 (d, J ¼ 8.00 Hz,
Hz, 1H, CH-arom.), 7.73–7.76 (d, J ¼ 7.20 Hz, 1H, CH-arom.),
7.61–7.64 (dd, J ¼ 7.20, J ¼ 7.60 Hz, 2H, CH-arom.), 7.41–7.43 (m,
2H, CH-arom.), 5.64–5.66 (d, J ¼ 9.73 Hz, 1H, 70-CH), 5.17–5.20 (d,
J ¼ 9.72 Hz, 1H, 80-CH), 3.84 (s, 3H, 30-CH3), 3.36 (s, 3H, 20-CH3), 2.10
(s, 3H, 60-CH3), 1.57 (s, 3H, 80-CH3) ppm. 13CNMR (400 MHz, CDCl3)
d 163.64 (30-CO), 161.98 (20-CO), 148.64, 147.34, 144.46, 139.77,
138.13, 132.28, 131.48, 131.75, 129.63, 127.75, 121.10, 121.32,
121.12, 119.25, 101.57, 67.34 (80a-C), 66.67 (spiro-C), 53.22
(30-CH3), 51.24 (20-CH3), 22.41 (60-CH3), 21.31 (80-CH3) ppm; IR
(KBr): n ¼ 3097 (C—H, arom.), 2914–2983 (C—H, aliph.), 1746
165.31 (20-CO), 163.15 (CO-ethyl ester), 153.9, 149.82, 148.85,
148.65, 147.7, 142.70, 142.52, 139.13, 138.62, 138.34, 136.09,
136.01, 133.61, 133.37, 131.87, 130.06, 129.97, 128.83, 127.64,
124.25, 124.16, 123.91, 123.78, 122.01, 121.95, 121.39, 118.82,
117.71, 112.64, 105.86, 93.41 (acetylenic-C), 89.34 (acetylenic-C),
88.17, 65.67 (80a-C), 63.38 (spiro-C), 61.53, 52.65 (30-CH3), 51.40
(20-CH3), 46.91, 39.73, 30.08, 26.24, 24.94, 23.80, 22.86, 22.14,
14.57, 12.20 ppm; IR (KBr): n ¼ 3017S3067 (C—H, arom.),
0
—
2887–2981 (C—H, aliph.), 2211 (acetylenic bond), 1751 (3 -C
—
0
—
—
—
O), 1709 (CO-ester), 1691 (2 -C O), 1588 (C N), 1454 (C C),
—
—
—
1348, 1261, 1183, 1118, 956, 895, 767 cmꢁ1; HR-MS m/e (%)
1064.42 [Mþ]; Elemental Analysis for C68H60N2O10: C, 76.67; H,
5.68; N, 2.63; Found %: C, 76.65; H, 5.69; N, 2.64.
0
0
—
—
—
—
—
(3 —C O), 1681 (2 —C O), 1635 (C N), 1520 (C C), 1442,
—
—
—
1360, 1266, 1146, 1118, 976, 878, 760 cmꢁ1; HR-MS m/e (%)
665.95 [Mþ]; Elemental Analysis for C25H20I2N2O4: C, 45.07; H, 3.03;
N, 4.20; Found %: C, 45.06; H, 3.05; N, 4.19.
Dimethyl 2-(ethynylphenyl)-3,5,7-tris(4-carboethoxy)adamantyl-
20,4a0-dimethyl-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,
70-dicarboxylate 14b: From DHI 11b; R1
R
—
—
—
CH , method A,
—
2
3
yield ¼ 10%, mp ¼ 122 8C; method B, yield ¼ 16%, mp ¼ 123 8C;
—
—
—
—
method C, yield ¼ 18%, mp ¼ 122 8C; from DHI 11f: R1
R
2
Sonogashira-mediated coupling for the synthesis of
photochromic DHIs-tripodal-linker 14a–d: General
procedure (Best conditions)
CH3, method A, yield ¼ 22%, mp ¼ 123 8C; method B, yield ¼ 34%,
mp ¼ 123 8C; method C, yield ¼ 52%, mp ¼ 122 8C; method D,
yield ¼ 7%, mp ¼ 121 8C; method E, yield ¼ 9%, mp ¼ 121 8C.1H
NMR (400 MHz, CDCl3) d 8.32–8.36 (d, J ¼ 8.00 Hz, 1H, CH-arom.),
8.09–8.11 (d, 6H, J ¼ 8.72 Hz), 8.07–7.10 (d, J ¼ 8.00 Hz, 1H,
CH-arom.), 7.76–7.80 (d, J ¼ 7.20 Hz, 1H, CH-arom.), 7.60–7.63
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 the mono- and dihalo-substituted fluorene
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Copyright ß 2010 John Wiley & Sons, Ltd.
J. Phys. Org. Chem. 2011, 24 173–184

PHOTOCHROMIC DIHYDROINDOZILINE: TOWARD NANOTECHNOLOGY APPLICATIONS
(dd, J ¼ 7.20, J ¼ 7.60 Hz, 2H, CH-arom.), 7.40–7.43 (d, 6H,
J ¼ 8.72 Hz), 7.32–7.36 (d, 2H, J ¼ 8.60 Hz), 7.16–7.19 (d, 2H,
J ¼ 8.60 Hz), 7.05–7.09 (m, 2H, CH-arom.), 5.68–5.72 (m, 1H, 70-CH),
5.11–5.17 (dt, J ¼ 8.00 Hz, J ¼ 2.00 Hz, 80-CH), 4.50–4.53 (q, 6H,
J ¼ 7.12 Hz), 3.94 (s, 3H, 30-CH3), 3.49 (s, 3H, 20-CH3), 2.19 (two
overlapping, s, 12H), 2.12 (s, 3H, 60-CH3), 1.62 (s, 3H, 80-CH3), 1.42 (t,
1H, CH-arom.), 8.32–8.36 (d, 12H, J ¼ 8.72 Hz), 8.12–7.15 (d,
J ¼ 8.00 Hz, 2H, CH-arom.), 7.67–7.70 (d, J ¼ 7.20 Hz, 2H,
CH-arom.), 7.51–7.54 (dd, J ¼ 7.20, J ¼ 7.60 Hz, 3H, CH-arom.),
7.61–7.64 (d, 12H, J ¼ 8.72 Hz), 7.26–7.32 (d, 2H, J ¼ 8.60 Hz),
7.10–7.13 (d, 2H, J ¼ 8.60 Hz), 7.06–7.08 (m, 2H, CH-arom.),
5.88–5.92 (m, 1H, 70-CH), 5.18–5.23 (dt, J ¼ 8.00 Hz, J ¼ 2.00 Hz,
80-CH), 4.49–4.53 (q, 12H, J ¼ 7.12 Hz), 3.86 (s, 3H, 30-CH3), 3.44 (s,
3H, 20-CH3), 2.17 (two overlapping, s, 24H), 2.16 (s, 3H, 60-CH3), 1.53
(s, 3H, 80-CH3), 1.47 (t, 18H, J ¼ 7.12 Hz), ppm. 13CNMR (400 MHz,
CDCl3) d 166.43 (30-CO), 165.98 (20-CO), 164.16 (CO-ethyl ester),
153.94, 150.18, 148.79, 148.32, 148.47, 144.31, 143.63, 141.79,
140.36, 138.74, 138.30, 136.18, 136.03, 134.46, 133.74, 132.30,
131.79, 130.62, 127.50, 125.67, 123.16, 122.48, 122.00, 121.32,
118.38, 117.57, 112.21, 105.89, 93.47 (acetylenic-C), 89.35
(acetylenic-C), 88.67, 65.32 (80a-C), 63.52 (spiro-C), 61.64, 52.51
(30-CH3), 51.97 (20-CH3), 46.53, 40.28, 31.64, 26.31, 24.70, 23.18,
22.65 (60-CH3), 22.28, 21.16 (80-CH3), 14.85, 12.34, ppm; IR (KBr):
n ¼ 3100–3032 (C—H, arom.), 2910–2997 (C—H, aliph.), 2216
13
9H, J ¼ 7.12 Hz) ppm. CNMR (400 MHz, CDCl3) d 167.65 (30-CO),
165.35 (20-CO), 163.28 (CO-ethyl ester), 152.99, 150.34, 148.65,
148.79, 147.56, 142.62, 142.37, 139.63, 138.68, 138.67, 136.10,
136.85, 133.63, 133.47, 131.22, 130.19, 129.85, 128.64, 127.78,
124.61, 124.10, 124.02, 123.75, 122.18, 121.87, 121.46, 118.76,
117.26, 112.50, 105.81, 93.76 (acetylenic-C), 89.79 (acetylenic-C),
88.28, 65.41 (80a-C), 63.40 (spiro-C), 61.87, 52.41 (30-CH3), 51.23
(20-CH3), 46.89, 39.65, 30.18, 26.17, 24.85, 23.64, 22.37, 22.76
(60-CH3), 22.43, 21.13 (80-CH3), 14.13, 12.58, ppm; IR (KBr):
n ¼ 3069ꢁ3021 (C—H, arom.), 2895–2976 (C—H, aliph.), 2228
0
0
—
—
—
(acetylenic bond), 1748 (3 -C O), 1702 (CO-ester), 1687 (2 -C
—
—
—
O), 1586 (C N), 1450 (C C), 1379, 1261, 1175, 1136, 950, 887,
—
—
746 cmꢁ1; HR-MS m/e (%) 1092.46 [Mþ]; Elemental Analysis for
C70H64N2O10: C, 76.90; H, 5.90; N, 2.56; Found %: C, 76.89; H, 5.94;
N, 2.58.
(acetylenic bond), 1742 (3 -C O), 1713 (CO-ester), 1685 (2 -C
0
0
—
—
—
—
—
—
O), 1567 (C N), 1452 (C C), 1355, 1261, 1185, 1134, 947, 868,
—
—
751 cmꢁ1; HR-MS m/e (%) 1770.75 [Mþ]; Elemental Analysis for
115H106N2O16: C, 77.94; H, 6.03; N, 1.58; Found %: C, 77.93; H, 6.05;
N, 1.57.
Dimethyl
2,7-((bis(ethynylphenyl)-3,5,7-tris(4-carboethoxy)
C
adamanty)l-4a0H-spiro[fluorene-9,50-pyrrolo[1,2-b]pyridazine]-60,70-
—
—
—
H, method A,
—
dicarboxylate 14c: From DHI 11c; R1
R
2
yield ¼ 18%, mp ¼ 146 8C; method B, yield ¼ 14%, mp ¼ 147 8C;
Acknowledgements
—
—
—
H,
—
method C, yield ¼ 23%, mp ¼ 146 8C; from DHI 11g: R1
R
2
The author is highly indebted to Alexander von Humboldt
foundation (AvH) and Taibah University for financial support of
this work. He also thanks Prof. Dr Heinz Du¨rr (University of
Saarland, Saarbru¨cken, Germany), Prof. Dr Henri Bouas-Laurent,
and Prof. Dr Jean-Luc Pozzo (University of Bordeaux, France) for
their continuous helpful discussions and measurements.
method A, yield ¼ 29%, mp ¼ 145 8C; method B, yield ¼ 37%,
mp ¼ 146 8C; method C, yield ¼ 69%, mp ¼ 145 8C; method D,
yield ¼ 10%, mp ¼ 146 8C; method E, yield ¼ 12%, mp ¼ 145 8C.
1H NMR (400 MHz, CDCl3) d 8.22–8.24 (d, J ¼ 8.00 Hz, 1H,
CH-arom.), 8.10–8.14 (d, 12H, J ¼ 8.72 Hz), 8.04–7.07 (d,
J ¼ 8.00 Hz, 2H, CH-arom.), 7.60–7.63 (d, J ¼ 7.20 Hz, 2H,
CH-arom.), 7.49–7.55 (dd, J ¼ 7.20, J ¼ 7.60 Hz, 3H, CH-arom.),
7.46–7.9 (d, 12H, J ¼ 8.72 Hz), 7.20–7.26 (d, 2H, J ¼ 8.60 Hz),
7.02–7.05 (d, 2H, J ¼ 8.60 Hz), 7.08–7.14 (m, 2H, CH-arom.),
6.99–7.01 (dd, J ¼ 1.76, J ¼ 1.76, 1H, 60-CH), 5.72–5.73 (m, 1H,
70-CH), 5.36–5.40 (t, J ¼ 2.2 Hz, 1H, 80-CH), 5.06–5.08 (dt,
J ¼ 8.00 Hz, J ¼ 2.00 Hz, 8a0-CH), 4.42-4.48 (q, 12H, J ¼ 7.12 Hz),
3.92 (s, 3H, 30-CH3), 3.40 (s, 3H, 20-CH3), 2.19 (two overlapping, s,
24H), 1.48 (t, 18H, J ¼ 7.12 Hz) ppm. 13CNMR (400 MHz, CDCl3) d
166.98 (30-CO), 165.76 (20-CO), 164.01 (CO-ethyl ester), 153.91,
150.02, 148.95, 148.64, 148.02, 144.35, 143.67, 141.68, 140.27,
138.95, 138.20, 136.11, 136.11, 134.03, 133.87, 132.16, 131.64,
129.90, 128.84, 127.50, 125.67, 124.78, 123.05, 122.48, 121.17,
121.02, 118.24, 117.36, 112.13, 105.78, 93.87 (acetylenic-C), 89.01
(acetylenic-C), 88.46, 65.34 (80a-C), 63.57 (spiro-C), 61.43, 52.46
(30-CH3), 51.47 (20-CH3), 46.87, 40.21, 31.64, 26.38, 24.78, 23.34,
22.78, 22.24, 14.67, 12.29 ppm; IR (KBr): n ¼ 3117ꢁ3041 (C—H,
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Dimethyl
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method A, yield ¼ 14%, mp ¼ 126 8C; method B, yield ¼ 22%,
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CH , method A, yield ¼ 25%, mp ¼ 126 8C; method B,
2
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method D, yield ¼ 8%, mp ¼ 126 8C; method E, yield ¼ 11%,
mp ¼ 125 8C. 1H NMR (400 MHz, CDCl3) d 8.22–8.24 (d, J ¼ 8.00 Hz,
J. Phys. Org. Chem. 2011, 24 173–184
Copyright ß 2010 John Wiley & Sons, Ltd.
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