Oligothiophene-linked bisnaphthopyrans: Sequential and temperature- dependent photochromism

Article abstract of DOI:10.1002/chem.200600958

Photochromic bisnaphthopyrans linked with oligothiophenes were synthesized and their photochromic behavior studied. Sequential and temperature-dependent photochromism was observed in the oligothiophene linked bisnaphthopyrans. The kinetics of photo and thermal processes in bisnaphthopyrans in comparison with naphthopyrans were studied, Substituent and linking effects on the photochromic properties are discussed. We demonstrate that the cross-talk between the two photochromophores is dependent on the length of the oligothiophene linker. The presence of the bithiophene linker led to high colorability and high quantum yield of coloration.

Full text of DOI:10.1002/chem.200600958

FULL PAPER
DOI: 10.1002/chem.200600958
Oligothiophene-Linked Bisnaphthopyrans:
Sequential and Temperature-Dependent Photochromism
Weili Zhao and Erick M. Carreira*[a]
Abstract: Photochromic bisnaphthopyr-
ans linked with oligothiophenes were
synthesized and their photochromic be-
havior studied. Sequential and temper-
ature-dependent photochromism was
observed in the oligothiophene linked
bisnaphthopyrans. The kinetics of
photo and thermal processes in bis-
naphthopyrans in comparison with
naphthopyrans were studied. Substitu-
ent and linking effects on the photo-
chromic properties are discussed. We
demonstrate that the cross-talk be-
tween the two photochromophores is
dependent on the length of the oligo-
thiophene linker. The presence of the
bithiophene linker led to high colora-
bility and high quantum yield of colo-
ration.
Keywords:
heterocycles
dyes/pigments
· oligothiphene
·
·
photochromism · sensors
Introduction
benzodihydropyrene photochromophore examined dis-
played inverse photochromism. In the case of dihydroindoli-
zine, the observations made under laser-induced photolysis
were not carried over under continuous irradiation. None of
the above-mentioned systems are therefore satisfactory for
use in protective eye wear or in displays.
Over the last number of decades, photochromic dyes have
attracted considerable attention because of the wide range
of potential applications.[1,2] Recent interests have been fo-
cused on design, synthesis, and study of novel bisphotochro-
mophores.[3–10] We have recently documented the first bis-
naphthopyran showing sequential photochromism wherein
the color hue changes with time at room temperature under
UV irradiation.[9] In our continuing interest in the discovery
of bisphotochromophores displaying novel properties, we
have identified bisnaphthopyran systems which display tem-
perature-dependent photochromism. In this paper, we
report the detailed synthesis, photochromic behavior, and
mechanistic studies of such bisnaphthopyrans linked through
oligothiophene spacers.
A number of bisnaphthopyran systems have been report-
ed, wherein naphthalene subunits are linked via ethenes;
however, these display unwanted irreversible photoreac-
tions.[8c] When acetylenic linkages are employed either
normal photochromism or no photochromism is observ-
ed.[8b,e] Tetrathiafulvalene (TTF)-containing bisnaphthopyr-
ans display weak photochromism.[8j] The use of flexible link-
ers for the pyrans or, alternatively, fusion of both these units
onto a common naphthalene unit fails to lead to novel pho-
tochromism.[8g–i] Recently, bis-[3H]-naphtho
[2,1-b]pyrans
A
Among the known bisphotochromic systems reported,[3–10]
only a few exhibit behavior that differs significantly from
the monomeric counterpart. Studies of covalently-linked in-
teractive photochromophores have been observed only in a
few cases involving diarylethene and bisbenzodihydropyrene
under continuous irradiation,[3g–l,4] and in dihydroindolizine
under laser-induced photolysis.[7b] However, in the former
cases, the photogenerated colored form of the diarylethene
is thermally stable and fails to undergo fading; and the bis-
linked at the sp3-hybridized carbon of the pyrans with ter-
thiophene or quaterthiophene were reported;[10] however,
no kinetic parameters were documented for these systems.
Such terthiophene and quaterthiophene linked bisnaphtho-
pyrans are expected to have low photoconversion because
of fast fading rate due to the substitution by the electron
rich units employed, as well as inherent fluorescence of the
oligothiophene linker.[8b]
We have chosen to synthesize and investigate molecules
wherein two pyran units are linked through an electron rich
bithiophene linker, which is known to afford systems dis-
playing high colorability.[11] In this respect, we have been in-
terested in the influence of linker size on the photochemical
properties of bisnaphthopyrans. Implementation of the plan
of study has led to the synthesis of 1a–h (see below), which,
[a] Dr. W. Zhao, Prof. Dr. E. M. Carreira
Laboratorium für Organische Chemie, ETH Zürich, HCI H335
8093 Zürich (Schweiz)
Fax : (+41)1-632-1328
E-mail: carreira@org.chem.ethz.ch
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apolar solvent such as toluene.[13] We recently reported a
facile one-pot synthesis of naphthopyrans using pyridinium
p-toluenesulfonate (PPTS) as the catalyst in combination
with trimethyl orthoformate as dehydrating agent.[14] The
application of this methodology to the preparation of thio-
phene substituted naphthopyran compounds affords 2a–i in
excellent yields. The starting aromatic thienyl ketones were
synthesized by Friedel-Crafts reaction of thiophene precur-
sor 3 with aroyl chloride in dry CH2Cl2 by using tin tetra-
chloride as catalyst, which afforded the desired ketones 4a–i
in good to excellent yields. The required 3,3-disubstituted
propargyl alcohols 5a–i were synthesized from aromatic ke-
tones by reaction with sodium acetylide. We noted that the
use of excess acetylene gas in the reaction mixture through
its continuous bubbling is helpful in reducing the amount of
side product (2-butyne-1,4-diol derivative) resulting from
double addition.[15] This protocol represents a useful im-
provement to the preparation of these building blocks. Thus,
although 5h was reported in yield of 36% using 3 equiv of
sodium acetylide in xylene,[16] it could be prepared in yield
of 71% by using only 1.68 equiv of sodium acetylide with
this modified procedure.[14] The homo-coupling reaction of
thienyl naphthopyran was performed in THF with the lithi-
ated species at low temperature using cupric chloride (1.6–
2.0 equiv) as oxidant. Good to excellent yields (55–97%) of
bisnaphthopyrans were obtained from various thienyl naph-
thopyrans.
as detailed below, furnishes novel systems wherein covalent-
ly coupled photochromophores work synergistically.
Results and Discussion
Synthesis of bisnaphthopyran 1a–h: The approach which has
been employed for the preparation of bisnaphthopyrans,
such as 1h, has been to couple 5,5’-bis-trimethyltin-2,2’-bis-
thiophene and the corresponding substituted 2-(4-bromo-
thienyl)-[3H]-naphtho[2,1-b]pyrans via Stille cross-cou-
G
pling.[10a,12] The low yield (43%) and the use of the distannyl
bithiophene detract from the appeal of such a method. The
attempted synthesis of bisnaphthopyrans via copper promot-
ed homo-coupling of bromothienyl pyran was unsuccess-
ful.[10a] We have developed a complementary approach to
the coupling of naphthopyrans involving the lithiation of the
terminal thiophene followed by a copper-promoted homo-
coupling (see 2 ! 1, Scheme 1).
Due to the symmetric nature of bisnaphthopyrans 1a–h,
1
the H NMR spectra are relatively simple. The characteristic
1H NMR resonance for the vinyl proton adjacent to the
carbon bearing the heteroatom (O) for 1c–e and 1g–h (the
non-fluorinated compounds) can be found as doublets at d
The most commonly used method for preparation of
naphthopyrans is based on the Claisen rearrangement of
propargyl naphthol ethers, which can be made in situ from
naphthol with diaryl propargylic alcohol in the presence of
catalytic amounts of acid catalyst (typically, TsOH) in an
6.0–6.3 ppm with
a coupling constant of 10 Hz. The
13C NMR of the sp3-hybridized carbon is also characteristic,
appearing at about 80 ppm. In the case of fluorine substitut-
ed bisnaphthopyrans, coupling
patterns are consistent with
those reported for similarly-
substituted fluorinated pyr-
ans.[8f] For example, the vinyl
proton adjacent to the heteroa-
tom in the ortho-fluorophenyl
substituted bisnaphthopyran 1a
appears as a doublet of dou-
1
blets in the H NMR spectrum
5
due to JH,F coupling and as a
doublet in the 13C NMR spec-
5
trum due to JC,F coupling.[8f]
Photochromism of bithiophene
linked bisnaphthopyran 1a–e in
solutions: All of the bisnaph-
thopyrans 1a–h synthesized in
this study as well as their pre-
cursors (2a–i) are photochro-
mic. The mechanistic details of
the photochromism of the mon-
Scheme 1. Synthesis of bisnaphthopyran 1. i) acyl chloride (1.04 equiv), SnCl4 (1.04 equiv), CH2Cl2, À4 to
238C: 4a, 98.0%; 4b, 91.1%; 4c, 89.6%; 4d, 92.6%; 4e, 98.0%; 4 f, 44.5%; 4g, 62.0%; 4h, 67.7%; 4i, 57.8%;
ii) sodium acetylide (1.4–2.0 equiv), DMSO, acetylene, 2–3 h, 238C: 5a, 60.2%; 5b, 82.4%; 5c,[17] 74.5%; 5d,
86.6%; 5e, 84.1%; 5 f, 82.7%; 5g, 86.6%; 5h, 71.0%; 5i, 82.7%; iii) 2-naphthol (1.0 equiv), PPTS (5 mmol%),
238C to reflux, (CH2Cl)2: 2a, 88.8%; 2b, 98.2%; 2c, 97.0%; 2d, 95.3%; 2e, 92.0%; 2 f, 89.2%; 2g, 92.4%; 2h,
83.5%; 2i, 94.5%; iv) nBuli (1.6m, 1.6 equiv), CuCl2 (1.6–2.0 equiv), À78 to 238C, overnight: 1a, 72.7%; 1b,
55.0%; 1c, 96.5%; 1d, 77.1%; 1e, 65.5%; 1 f, 76.9%; 1g, 88.2%; 1h, 83.5%.
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Photochromism
FULL PAPER
omeric precursor pyran 2 are shown in Scheme 2. It is well-
known that the original state of compound 2 is the closed
pyran form (closed). Upon exposure to UV irradiation, the
slowly; however, it is susceptible to rapid bleaching upon ir-
radiation with visible light.
Compound 1a has absorption maxima (l, in nm) and ex-
tinction coefficients (e, in molÀ1 dm3 cmÀ1) at 306 (sh)
(26700), 318 (33800), 333 (sh) (28400), which are similar to
the absorption maxima displayed by bithiophene 2 f [306
(sh) (20700), 317 (23400)] but with larger extinction coeffi-
cients. Monothiophene 2a [304 (5520), 316 (6400), 346
(4360), and 358 (4200)] has quite different absorption from
either 1a or 2 f (see Figure 2). By comparing Figure 1 and 2,
Scheme 2. Photochromic reaction of pyran 2.
colored species generated are the more abundant and fast-
fading trans–cis (TC) and the trans–trans (TT), which is
present as a minor component and is most stable.[12] The TC
form has been shown to be generated preferentially in the
early stages of the photocoloration process.[18] These (TC
and TT) can undergo thermal fading, and the bleaching pro-
cess can be enhanced photochemically with visible light.
The color change and UV spectra of photochromophoric
bispyran 1a upon UV irradiation in toluene at room temper-
ature are shown in Figure 1. The near colorless solution of
Figure 2. UV-visible spectra of compound 2a (top) and 2 f (bottom)
(both 2.5”10À5 m in toluene) prior to and after UV (366 nm) irradiation
for 5 s and 2 min at room temperature.
it is clear that bithiophene linked bisnaphthopyran 1a has
greater similarity to compound 2 f with a bithiophene sub-
stituent than to monothiophene 2a. Upon exposure to UV
light, the absorption maxima remain almost unchanged fol-
lowing UV irradiation for 5 s and 2 min, respectively, for
both 2a and 2 f.
Figure 1. UV-visible spectra of compound 1a (2.5”10À5 m in toluene)
prior to and after UV (366 nm) irradiation for 5, 30 s and 4 min at room
temperature.
The dramatic change of color hue of bisnaphthopyran 1a
upon extended periods of irradiation with UV light suggests
that a sequential photochromic process has taken place in
1a, namely ring-opening and coloration of the second naph-
thopyran unit takes place following the opening of the first
naphthopyran unit upon extended irradiation. In contrast to
1a, no sequential photochromism was observed for 1b at
room temperature. When a solution of compound 1b in tol-
uene was irradiated with UV (366 nm) at ambient tempera-
1a (2.5”10À5 m in toluene) rapidly undergoes coloration to
orange-red after irradiation with UV (366 nm) for 5 s. Expo-
sure of 1a for extended periods of time produced interesting
results. The color hue changed to red-purple after 30 s and
to purple-blue after 4 min. Removal of the irradiation
source resulted in fading of the color in the reverse order.
After 30 min a residual color persists (pale red), which fades
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2673

E. M. Carreira and W. Zhao
ture, the colorless solution turned to red rapidly, however,
no change of color hue was observed under prolonged (even
intense) irradiation, which suggests that the position of fluo-
rine substituent plays important role in the photochromic
behavior of bisnaphthopyran 1a/1b.
to the opening of the second photochromic unit in the bis-
pyran molecule 1b. The discovery of sequential photo-
chromism in 1a and temperature-dependent photochromism
in 1b prompted us to investigate the photochromism of
these bisnaphthopyrans in quantitative manner.
It is known that ortho-fluoro substitution slows down the
fading rate dramatically compared with para-fluoro substitu-
tion in photochromic pyran systems.[13] The main difference
between 1a and 1b is that the thermal fading in 1a is slow,
however in 1b is fast. We speculated that by lowering the
temperature to slow down the fading process, sequential
photochromism would then be observed in 1b. Consistent
with this hypothesis, when a cold solution of 1b was irradiat-
ed with UV light, the colorless solution changed to purple
(58C) and to purple-blue (À108C) gradually (see Figure 3).
A number of mathematical approximations and simula-
tions have to be used for the kinetic study of photochromic
pyrans wherein the reversible thermal and photochemical
processes involve more than two colored species.[20,21] Addi-
tional difficulties are expected for the kinetic study with bis-
naphthopyrans 1a/1b as a consequence of the two photo-
chromic units present in the same molecule.
We proceeded to identify the colored species generated
with 1a after UV irradiation. In prior work, it has been
demonstrated that the fast fading colored species (TC) of
2,2-di(4-fluorophenyl)-6-methoxy-2H-1-chromene generated
by UV irradiation has half life time (t1/2) about 1.5 h at
À458C.[22] With this background information in hand, we
proceeded to isolate the various colored intermediates gen-
erated by UV irradiation through the use of low-tempera-
ture chromatography (À788C).
Chromatographic separation at low temperature was first
applied to the known 3,3-diphenyl-[3H]-naphtho[2,1-b]pyran
U
as a control experiment in order to check the validity and
feasibility of the method for the separation of unstable col-
ored species. We managed to isolate two colored species:
one during the early stage of irradiation, which is assigned
to the TC form and a second minor, which is more stable,
and thus assigned to the TT form. The isolated TC form has
e value of 18100 molÀ1 dm3 cmÀ1 at the absorption maximum,
and
the
isolated
TT
form
displays
e
=
16900 molÀ1 dm3 cmÀ1. The former is in good agreement to
the previously reported simulation data, while the latter is
not. However, as noted in the earlier simulation work,[20a]
the large error associated with the predicted value for the
miniscule amounts the TT form casts into question the accu-
racy of this value.
Figure 3. UV/Vis spectra of compound 1b (2.3”10À5 m in toluene) prior
to and after UV (366 nm) irradiation for 4 min at various temperature. a)
Prior to UV irradiation; b) UV irradiation at ambient temperature; c)
UV irradiation at 58C; d) UV irradiation at À108C.
For comparison, the color hue of reference compound 2i
upon UV irradiation remains unchanged in the same range
of temperature, and only an increase in intensity of the
color was observed. For 1b in the dark, the color faded
through the color sequence observed during coloration, but
in reverse. Thus 1b displays interesting temperature-depen-
dent photochromism.
Temperature-dependent photochromism had been ob-
served in spiropyran systems bearing a spiroindoline ring at
the sp3-hybridized carbon adjacent to a pyran oxygen at
very low temperature (ꢀÀ808C). This has been attributed
to the thermal equilibration between various colored species
generated from the same photochromophore, as well as to
aggregates of the colored forms.[19] A noteworthy difference
between the spiroindolinepyran and pyran photochromo-
phores is that the pyran system generates a quinoid in its
open form whereas the spiropyran is transformed into a
zwitterionic open form.[1,13] In our dimeric pyran system, we
believe that the mechanism of temperature-dependent pho-
tochromism is completely different from the spiropyran due
Upon irradiation of 1a, two red and one purple-blue spe-
cies could be identified. Three different separation strategies
were employed in order to isolate and examine these indi-
vidually. For the separation of the fast-fading red compound
with absorption at 517 nm at ambient temperature, a solu-
tion of 1a was irradiated at 366 nm for 5 s at À308C in
CH2Cl2/hexane 2:1 and then transferred to a column of
silica gel at À788C. Elution initially with cold CH2Cl2 fol-
lowed by CH2Cl2/Et2O 100:1 under slight vacuum permitted
the collection of various fractions into thick-walled tubes
which were immersed in liquid nitrogen. These fractions
were then transferred to a pre-cooled cuvette in an Oxford
Cryostat; as the frozen fractions partially melted, the UV/
Vis spectrum was acquired at À788C. The colored solution
isolated was allowed to warm up to room temperature and
was kept in dark until complete fading of the color had
been observed. The absorption spectrum of bisnaphthopyran
1a that had been isolated through the procedure described
was compared to a standard solution of 1a. In such manner
the concentration of the isolated colored form could be de-
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Photochromism
FULL PAPER
termined. The spectrum of isolated colored form (red, fast
fading) of 1a has the same shape as the one generated at
room temperature by exposure to UV irradiation for 5 s.
The intensity of the spectrum taken at room temperature
was 85% intensity of the one taken at À788C due to the
change of the volume of the solvent. Thus the extinction co-
efficient of the isolated colored form (converted to the
value at room temperature) could be calculated according
to Lambert–Beer law to be 303 (27200), 317 (24600), 358
(21900), 514 (29200).
these colored species of 1b was identical to that detailed for
1a. The spectra of isolated colored species of 1b are shown
in Figure 5. The spectroscopic data for 1a and b as well as
reference compounds 2 f and i are collected in Table 1.
For separation of the more stable red species present in
minor quantities generated from 1a, it was exposed to UV
(366 nm) for an extended period of time. A solution of com-
pound 1a in CH2Cl2/hexane 2:1 was initially irradiated with
UV (366 nm) for 50 s at 208C and was allowed to fade at
room temperature so as to eliminate the fast fading red spe-
cies as monitored with a Cary 50 UV/Vis spectrometer at
510 nm. The partially faded solution of 1a was resubmitted
to another cycle of irradiation along with fading as de-
scribed above, and then the colored solution was loaded on
a pre-cooled column (À788C) of silica gel. Elution with cold
CH2Cl2 followed by CH2Cl2/Et2O 100:1 under slight vacuum
permitted the collection of various fractions into thick-
walled tubes which were immersed in liquid nitrogen and
treated as described for the fast-fading red species. The ex-
tinction coefficient of the isolated red species displaying
slow fading rate was calculated to be 303 (19000), 317
(19700), 360 (19400), 523 (25200) at room temperature.
For the separation of the purple-blue colored species, 1a
in CH2Cl2/hexane 2:1 was irradiated with UV (366 nm) for
4 min at À308C, and the chromatographic separation was ef-
fected following a similar protocol. The extinction coeffi-
cient of the isolated purple-blue species with slow fading
rate was calculated to be 282 (26300), 370 (17700), 500sh
(26900), 593 (47800). The spectra of isolated colored species
of 1a at À788C are superimposed and shown in Figure 4.
Compound 1b displayed the same number of colored spe-
cies at low temperature. The protocol for the isolation of
Figure 5. Absorption spectra of the colored species generated from 1b
isolated by low-temperature chromatography on silica gel at À788C in
CH2Cl2/Et2O 100:1.
Table 1. Spectroscopic data of bisnaphthopyrans and reference pyrans in
CH2Cl2 as well as their colored forms in CH2Cl2/Et2O 100:1. e is in the
unit of molÀ1 dm3 cmÀ1
.
Compound e[a] closed–closed e closed-TC e closed-TT e open–open
1a 306sh 303 303 289
(26800) (27200) (21200) (22000)
318 317 316 366
(33800) (24600) (18700) (15400)
333sh 358 359 574
(28100) (21900) (21100) (42200)
514 514
(29200) (23900)
303 303
(17700) (19000)
317 317
(17800) (19700)
360 360
(22000) (19400)
527 523
(29000) (25200)
A
G
A
ACHTREUNG
A
G
A
ACHTREUNG
A
G
A
ACHTREUNG
A
ACHTREUNG
1b
306sh
(26200)
318
(33200)
333sh
(28000)
282
(26300)
370
(17700)
500sh
(26900)
593
(47800)
A
N
G
ACHTREUNG
G
ACHTREUNG
U
ACHTREUNG
ACHTREUNG
Compound
e* closed
e TC
e TT
2 f
306sh
295
283
A
N
ACHTREUNG
A
N
ACHTREUNG
A
ACHTREUNG
2i
306sh
(21300)
317
(23900)
G
A
ACHTREUNG
U
A
ACHTREUNG
Figure 4. Absorption spectra of the colored species of 1a isolated by low-
temperature chromatography on silica gel at À788C in CH2Cl2/Et2O
100:1.
AHCTREUNG
[a] In CH2Cl2.
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E. M. Carreira and W. Zhao
The coloration behavior of bisnaphthopyrans 1c–e is simi-
lar to that of 1b. The photochromic mechanism of 1a–e is
shown in Scheme 3. On the basis of prior work in this area,
measured by the standard procedure using potassium fer-
rioxalate actinometer to be 4.99”10À6 EinsteinsÀ1 dmÀ3.[23]
Under irradiation with 366 nm light, Aclosed–closed = 0.437 for
1b. The absorbance at 527 nm
for 50 mm solution of 1b in
CH2Cl2 upon UV irradiation at
300 K is shown in Figure 6a. We
assume that the small differen-
ces (3 nm) in the absorption
maxima at room temperature
from the one at À788C will not
affect the value of e. We also
noted that there is no differ-
ence of the absorbance of pho-
tochromic
compounds
in
CH2Cl2 from the one in
CH2Cl2/Et2O 100:1 so that we
could directly use the e value
from Table 1 for the calcula-
tions. (dAclosed-TC/dt)t!0 could be
obtained from a linear fitting of
photocoloration shown in Fig-
ure 6b. When the change of ab-
sorbance (dAclosed-TC/dt) was
plotted against absorbance A,
Scheme 3. Photochromic reaction of bisnaphthopyran 1a–e.
it is reasonable to attribute the fast-fading red species to the
s-trans–cis forms (only one isomer of the two is shown as
closed-TC); the red species generated with slow thermal
fading rate can be assigned to the s-trans–trans forms (only
one isomer of the two is shown as closed-TT). The purple-
blue species results from further irradiation and is generated
upon opening of both pyran units to a form with extended
conjugation (only one isomer is shown as open–open).
With the data presented, the quantum yield for the gener-
ation of the fast-fading red species can be calculated. In gen-
eral at an early stage of the photocoloration reaction, we
speculate that closed-TC was formed preferentially upon ex-
posure to UV, as has been claimed in photochromic
pyrans.[18] This allows simplification of the photochromic
sequence, which can then be described with the accompany-
F
ƒ!
ing equation: closed–closed
closed-TC dAclosed-TC/dt =
ƒ
k
À1
[20b,21]
e
closed-TCFI0
[1Àexp(À2.3Aclosed–closed)] À kÀ1Aclosed-TC
.
The maximum absorbance of closed-TC is defined by
Aclosed-TC. The extinction coefficient of closed-TC (eclosed-TC) is
collected in Table 1; F corresponds to the quantum yield of
the photoreaction. I0 is defined as the intensity of the inci-
dent light. Similarly, Aclosed–closed is the absorbance of closed–
closed at the irradiation wavelength (366 nm). By plotting
dAclosed-TC/dt versus Aclosed–closed and extrapolating the color-
forming rate to zero time, the quantum yield F could be
calculated using:
exp(À2.3Aclosed–closed)]}.
F
=
(dAclosed-TC/dt)t!0/{eclosed-TCI0
A
Photocoloration was performed with a 50 mm solution of
photochromic compounds in a thermostated quartz cuvette
irradiated with UV (366 nm) at a 908 angle to the monitor-
ing beam and was monitored at absorption maxima of the
colored forms with a Cary 50 UV/Vis spectrometer. I0 was
Figure 6. Photocoloration of compound 1b in CH2Cl2 (5”10À5 m) at
300 K. a) Absorbance of closed-TC at 515 nm upon UV irradiation; b)
experimental data treated according to Equation (1).
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Photochromism
FULL PAPER
very good linear relationship with a correlation coefficient
better than 0.99 was obtained. Thus (dAclosed-TC/dt)t!0 was
calculated to be 0.070. Repetition of three parallel measure-
ments allowed the determination of F as 0.76ꢁ0.01.
and i were also measured. The data obtained are collected
in Table 2.
Table 2. Kinetic parameters of bisnaphthopyran 1a–e and reference com-
pound 2 f, and 2i in CH2Cl2.
We next proceeded to determine the fading rate of the
fast-fading red species. Upon removal of the irradiation
source, the thermal fading process could be followed with a
Cary 50 UV/Vis spectrometer. In general, in this field biex-
ponential fading processes are involved for these processes.
Upon short irradiation (t = 6 s), due to the low content of
slow fading closed-TT, the fading process is dominated by
closed-TC and could be simplified and represented as a
monoexponential process. The fading of color monitored at
527 nm at 298.4 K for a 50 mm solution of 1b in CH2Cl2 after
5 s of UV (366 nm) irradiation is shown in Figure 7a. Mathe-
matic manipulation of the curve in Figure 7a by plotting dA/
dt versus time leads to good linearity (correlation coefficient
better than 0.99) and the rate of thermal fading for closed-
TC was calculated to be 0.165 sÀ1 at 298.4 K. By measuring
fading rate at various temperatures, the activation energy
(Ea) of thermal fading of closed-TC for 1b could be ob-
tained from Arrhenius plots as shown in Figure 7b and was
calculated to be 56.95 kJmolÀ1.
Compound
F (300 K)
kÀ1 [sÀ1] (298.4 K)
Ea [kJmolÀ1
]
1a
1b
1c
1d
1e
2 f
2i
0.72
0.76
0.95
0.0405
0.151
0.126
0.171
0.278
0.0382
0.167
60.93
56.95
[a]
–
–
–
[a]
[a]
–
–
[a]
[a]
0.76
0.81
64.11
56.30
[a] Not measured.
The photochromic bispyrans 1a–e display similar kinetics
for both photocoloration and fading to that observed for ref-
erence compound 2 (1a versus 2 f and 1b versus 2i) with
same substitution pattern. Bithiophene-linked bispyrans 1a–
e and bithiophene-substituted pyrans 2 f and 2i all have very
efficient photocoloration processes. The thermal fading rate
is dependent on the substitution pattern. In 1a and refer-
ence 2 f, the ortho-fluoro substituent leads to high energy
barrier and slow fading. The unsubstituted or para-substitut-
ed pyran systems along with the bispyran 1b–e display fast
fading, which is promoted by substitution with electron-do-
nating groups.
In a similar fashion, the coloration and thermal fading for
all other bispyrans as well as for reference compounds 2 f
The extinction coefficients for 1a–e in CH2Cl2 and in tolu-
ene fall within a narrow range. For example for compound
1a, the extinction coefficients in toluene are: 306sh (25700),
318 (32900), 333sh (28300), which are very close to the
values in CH2Cl2. Assuming the e value of the colored spe-
cies does not change in CH2Cl2 and in toluene, we could es-
timate the quantum yield (300 K) for photocoloration of bis-
naphthopyrans in toluene: 1a, 0.76; 1b, 0.76; 1c, 0.97; 2 f,
0.81; 2i, 0.82.
We next conducted a study of the fluorescence of the bi-
thiophene-linked bisnaphthopyrans, in order to gain insight
into the novel properties of bisnaphthopyran 1a–e. In gener-
al, for bisphotochromophores, only one photochromic unit
operates in most cases. Irie et al. attributed the failure of op-
eration of the second photochromic unit in dimeric diaryle-
thene systems to intramolecular energy transfer.[3e] In our
bisnaphthopyran systems, we observed clearly the sequential
photochromism in 1a at room temperature and in 1b–e at
low temperature.
The absorption and fluorescence spectra of 1a are shown
in Figure 8. Very weak fluorescence of 1a was observed with
quantum yield estimated to be only 0.00013 by using 9,10-di-
phenylanthracene as the standard.[24] The colored species
formed from 1a (closed-TC, closed-TT, and open–open) do
not show any detectable fluorescence at room temperature,
which suggests that intramolecular energy transfer does not
seem to occur from the colored forms of 1a. Consequently,
the high reaction quantum yield and lack of efficient intra-
molecular energy transfer pathway may probably explain
the sequential photochromism in 1a.
Figure 7. a) Thermal bleaching of the colored species of compound 1b at
298 K after UV activation; b) Arrhenius plots of the kinetic parameters
of closed-TC.
Chem. Eur. J. 2007, 13, 2671 –2685
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E. M. Carreira and W. Zhao
Figure 8. Absorption spectra of bisnaphthopyran 1a (5.0”10À5 m) and
fluorescence spectra of 1a (A=0.04 at 353 nm) in chloroform at room
temperature.
Fatigure-resistance of bisnaphthopyran 1a–e: Fatigue is the
main limitation to the commercialization of many photo-
chromic dyes as variable-transmission materials. The pres-
ence of two photochromic units in bisnaphthopyran systems
led to the investigation of these systems and their resistance
against fatigue in comparison to the simple pyran systems.
Fatigue-resistance of photochromic compounds has been
known to be influenced by many factors.[25] On the basis of
earlier work, it was far from clear whether bisphotochromic
compounds would display enhanced fatigue resistance. For
example, in the single report of dimeric photochromophores
these are documented to be less fatigue-resistant than their
monomers, presumably due to the negative influence of rad-
ical products generated from one photochromic moiety on
the second unit.[5k]
The data collected in Table 2 suggest that the photochro-
mic processes of 1a–e are similar to the corresponding bi-
thiophene substituted pyrans (compare 1a versus 2 f and 1b
versus 2i). These therefore provide an ideal system with
which to compare the fatigue-resistance of bisnaphthopyr-
ans. We thus performed the photodegradation measurement
for 1b in comparison with 2 f under continuous exposure to
UV (366 nm) at 258C of a solution of 1b or 2 f. Bisnaphtho-
pyran 1b provides higher colorability and better fatigue-re-
sistance than reference 2i at the same concentration, howev-
er, this is not the case per photochromic unit (Figure 9).
Sequential photochromism was observed for bisnaphtho-
pyran 1a. However, in this system both photochromic units
operate, resulting in broad absorption. The open–open form
is likely more susceptible to fatigue than singly open forms
(closed-TC and closed-TT) as shown in Figure 10.[26]
Figure 9. Photodegradation and normalized degradation of compound 1b
(2.5”10À5 m) in comparison with reference compound 2i (2.5”10À5 m and
5”10À5 m, respectively) in toluene at 25.58C under white light irradiation.
tion, strong fluorescence was observed (see Figure 11). The
fluorescence quantum yield was measured to be 0.1 in 1 f
relative to 9,10-diphenylanthracene,[24] which suggests that
the fluorescence was derived from the quaterthiophene
tether. As a result of fluorescence, the photocoloration
quantum yields were small, approximately 0.1 (see Table 3).
In stark contrast, the colored forms of 1a–h do not have any
observable fluorescence. So that even with low photocolora-
tion quantum yield, the sequential and temperature-depen-
dent photochromism were still observed in 1a–h presumably
due to lack of the pathway for intramolecular energy trans-
fer.
Substitution effect and linking effect: In the bisnaphthopyr-
an systems we have investigated 1a–h, we have demonstrat-
ed that unusual communication between the two pyran units
is possible, which results in unexpected sequential photo-
chromism and temperature-dependent photochromism.
The absorption data for 1a–h are collected in Table 4.
The absorption maxima of bisnaphthopyrans were mainly
determined by the electron-rich oligothiophene linkers. The
absorption maximum in CH2Cl2 was 318 nm for molecules
containing bithiophene linkers and 406 nm for those with
quaterthiophene linkers, which was affected only a small
amount by substitution on phenyl moiety. This also suggests
Photochromism of quaterthiophene linked bisnaphthopyran
1 f–h: The quaterthiophene-linked bisnaphthopyrans 1 f–h
have much lower photocoloration quantum yields than the
bithiophene linked bisnaphthopyrans 1a–e.
In bisnaphthopyrans 1 f–h, there is strong absorption in
the region of 300–470 nm with extinction coefficients greater
than 42000mÀ1 cmÀ1 at 406 nm in CH2Cl2. Under UV irradia-
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Photochromism
FULL PAPER
Table 3. Kinetic parameters of bisnaphthopyran 1 f–h.
Compound
F (300 K)
Ff (298 K)
k [sÀ1] (298.4 K)
toluene
CHCl3
CH2Cl2
1 f
1g
1h
0.097
0.109
0.104
0.116
0.0067
0.091
0.162
[a]
–
[a]
–
[a] Not measured.
colorability decreased concomitantly with the increasing
electron donating ability of the para-substituents. Incorpora-
tion of ortho-substitution results in slow fading of the col-
ored forms, as a consequence, increased colorability was ob-
served. The slow fading allows the photochromic reaction of
the second unit to take place as shown in the cases of 1a
and 1 f, wherein sequential photochromism was observed at
room temperature. The value of the bathochromic shift be-
tween bisopen forms and monoopen forms are 62 nm for bi-
thiophene linked bispyran 1a and 25 nm for quaterthio-
phene linked bispyran 1 f, respectively, which suggests that
interaction between the two photochromic units in bisnaph-
thopyrans 1 f–h becomes less important with the increased
length of oligothiophene linker.
Fatigue-resistance is normally evaluated by the time re-
quired for decrease of absorbance at absorption maximum
to the half value of the initial colored forms at the photosta-
Figure 10. Photodegradation and normalized degradation of bisnaphtho-
pyran 1a (2.5”10À5 m) in comparison with reference 2 f (2.5”10À5 m) in
toluene at 25.58C under white light irradiation.
1
tionary state (t = ). However, it is difficult to maintain the
2
measurement of fatigue-resistance under identical condi-
tions for a long time. We thought it is more convenient in
our bisnaphthopyran system to compare the relative photo-
stability to the well-known 3,3-diphenyl-naphtho
by adjusting the fatigue of 3,3-diphenyl-naphtho
ACHTREUNG
AHCTREUNG
to about 75% in 1 h under continuous irradiation. The re-
sults are collected in Table 5.
Most of the bisnaphthopyrans display better stability than
3,3-diphenyl-[3H]-naphtho[2,1-b]pyran. The substitution at
G
the para position of the phenyl moiety leads to better fati-
gue-resistance than the substitution at the ortho position
due to increased fading rate. The photostability of bisnaph-
thopyran decreases with increased electron donating ability
of the substituent in phenyl albeit with increased fading
rate. The improved photostability of quaterthiophene linked
bisnaphthopyran 1 f–h may be due to the low quantum yield
of photochromic process.
Figure 11. Absorption and fluorescence spectra of bisnaphthopyran 1 f
(5.0”10À5 m) in chloroform at room temperature.
that the two pyran units are
Table 4. Absorption maxima (l) of bisnaphthopyran 1a–h (2.5”10À5 m) and their colored forms (lcol), as well
as the absorbance (A0) of the colored forms at photostationary state under irradiation in CH2Cl2 at room tem-
perature.
well insulated in bisnaphthopyr-
ans 1a–h. In contrast, the ab-
sorption maxima in the colored
forms are affected both by the
substitution on phenyl and by
the oligothiophene linkers. In
this regard, the absorption
maxima of the colored forms
1a
1b
1c
1d
1e
1 f
1g
1h
l [nm]
lcol [nm]
318
510
318
511
318
515
318
516
318
520
406
542
406
550
406
550
572[a]
0.817
0.857[a]
567[a]
1.13
1.13[a]
A0
0.466
0.455
0.484
0.39
0.478
0.313
shift bathochromically, and the [a] Bisopen form (open–open).
Chem. Eur. J. 2007, 13, 2671 –2685
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E. M. Carreira and W. Zhao
Table 5. Relative photostability of bisnaphthopyran to 3,3-diphenyl-[3H]-
naphtho[2,1-b]pyran in toluene at room temperature.
temperature was controlled with RM6 LAUDA thermo-cryostat. The
temperature inside the cuvette was measured with a EBRO TFX 592 dig-
ital thermometer.
ACHTREUNG
1a
1b
1c
1d
1e
1 f
1g
1h
1H NMR spectra were recorded on a VARIAN Mercury 300 MHz spec-
trometer in CDCl3, all signals are reported in ppm with the internal
chloroform signal at 7.26 ppm. The data is being reported as (s=singlet,
d=doublet, t=triplet, m=multiplet or unresolved, coupling constant(s)
in Hz, and integration). 13C NMR spectra were recorded with 1H decou-
pling on a VARIAN Mercury 75 MHz spectrometer in CDCl3, all signals
are reported in ppm with the internal chloroform signal at 77.0 ppm as
standard.
A
1.04
1.14
1.05
1.02
0.93
1.13
1.17
1.15
[a]
(A1/A0)ref
0.88[b]
1.09[b]
[a] A0 is absorbance of the colored forms for bispyrans at absorption
maxima at photostationary state upon white light exposure, and A1 is the
absorbance of the colored forms at absorption maxima after 1 h white
light illumination. (A0)ref is the absorbance of the colored forms for the
reference compound 3,3-diphenyl-[3H]-naphtho[2,1-b]pyran at its absorp-
A
tion maxima at photostationary state upon white light exposure, and
(A1)ref is the absorbance of the colored forms for the reference compound
at its absorption maxima after 1 h white light irradiation. [b] Relative
photostability at the longest absorption maximum of bisopen forms
(open–open).
Infrared spectra were recorded on a Perkin Elmer Spectrum RX-I FT-IR
spectrophotometer as thin films or as solution in chloroform and are re-
ported as cmÀ1
.
Mass spectrometric measurements were performed by the mass spec-
trometry service of the LOC at the ETH Zürich.
Photoreaction was generally carried out in quartz container irradiated
with either 8 W or 40 W Camag UV Lamp, or with 150 W Medium Pres-
sure Hg Lamp from Heraeus Labor UV-Reaktorsystem.
Conclusion
Fluorescence measurements were performed on Fluorolog-3 fluorometer
(Model FL-3–22) and Aminco Bauman Series 2 Luminescence Spectrom-
eter. To obtain accurate excitation spectra, excitation monochromator
was calibrated by Xenon lamp scan. The emission monochromator was
calibrated using a mercury lamp. The response of the detector was cali-
brated with standard tungsten/halogen lamp. Fluorescence quantum yield
determination was performed in 10 mm quartz cuvette using 9,10-diphe-
nylanthracene as the standard (Ff = 0.95).[24] Non-degassed, spectroscop-
ic grade chloroform was used as solvent and very dilute solutions (A =
0.04) were adopted in the measurements to minimize reabsorption ef-
fects.
We have observed sequential and temperature-dependent
photochromism in oligothiophene linked bisnaphthopyrans,
and thus unusual interaction of the two chromophores. We
have demonstrated that the cross-talk between the two pho-
tochromophores is dependent on the length of the oligothio-
phene linker. The presence of the bithiophene linker leads
to high colorability and high quantum yield of coloration.
By contrast, the quaterthiophene linker results in much di-
minished quantum yield and colorability. Furthermore, the
General procedure for low-temperature chromatography: A solution of
photochromic compound in a mixture of CH2Cl2/hexane 2:1 in a quartz
container irradiated with UV (366 nm) was loaded onto a silica gel
column fitted with a cooling jacket which was filled with dry ice/acetone
under slight vacuum, then was eluted with initially cold CH2Cl2, followed
by CH2Cl2/Et2O 100:1 (cooled by either dry ice or liquid nitrogen) under
slight vacuum. The collected fractions in thick-wall tubes were immedi-
ately frozen with liquid nitrogen.
quaterthiophene-linked bisnaphthopyran also renders
a
system displaying strong fluorescence. In all the bisnaphtho-
pyrans studied, no fluorescence was detected for the colored
forms at room temperature. The photochromic bisnaphtho-
pyrans have similar fatigue-resistance to monopyran species.
The observations we have made along with the in-depth
mechanistic studies will open up new avenues for the design
of novel photochromic compounds. Studies aimed at identi-
fying other members of bisphotochromophores displaying
unusual optical behavior are underway and will be reported
as results become available.
a) Separation of closed-TC: The solution of compound 1a–c, or 1 f in
CH2Cl2/hexane 2:1 irradiated with UV light for 5 s at temperature
ꢀÀ308C was loaded on the silica gel column, and closed-TC was sepa-
rated following the general procedure.
b) Separation of closed-TT: The solution of compound 1a or b in
CH2Cl2/hexane 2:1 was irradiated with UV light for 50 s at 208C, the
fading of color was monitored with Cary 50 at 510 nm until very slow
fading was observed. This irradiation/fading procedure was repeated,
then the sample was loaded on the cold silica gel column, and closed-TT
was separated following the general procedure.
Experimental Section
General information: All reactions were performed using oven dried
glassware. 1,2-Dichloroethane and DMSO were dried over molecular
sieves 3 Š. CH2Cl2 and THF were dried by passing through two 4”36
inch columns of anhydrous neutral A-2 alumina (8”14 mesh; Macherey
und Nagel; activated under a flow of N2 at 3008C over night) to remove
water. Bithiophene was synthesized according to literature method.[27] All
chemicals were purchased from Aldrich and Fluka, and used as such. The
solvents used for UV/Vis, IR and fluorescence study are all spectroscopic
c) Separation of open–open: The solution of compound 1a or b in
CH2Cl2/hexane 2:1 irradiated with UV light for 4 min at temperature
ꢀÀ308C was loaded on silica gel column, and open–open was separated
following the general procedure.
TC and TT of compound 2 f and i, as well as 3,3-diphenyl-[3H]-naphtho-
A
tively.
grade. 3,3-Diphenyl-[3H]-naphtho
ACHTREUNG
Low-temperature UV measurements: The frozen fraction isolated by
low-temperature chromatography was transferred into a cuvette cooled
to À788C in Oxford Cryostat while the frozen solution partially melted,
then UV/Vis spectra were recorded in Cary 50 with Oxford Cryostat at
À788C. Spectra are corrected for background absorption.
Calculation of extinction coefficient: The spectra of isolated colored
forms of 1a–-c, f, 2 f, and i have the same shape as colored forms generat-
ed at room temperature by UV, however with slightly shifted absorption
maxima (< 5 nm). The absorbance was recorded at À788C (the spectra
recorded at room temperature was 85% intensity of the one recorded at
À788C due to the change of the volume of the solvent). The colored
yl)-[3H]-naphtho
yl)-[3H]-naphtho
dure.[14]
ACHTREUNG
ACHTREUNG
For flash chromatography technical grade solvents were used, which
were distilled prior to use. Chromatographic purification was performed
as flash chromatography using Brunschwig silica 32–63, 60 Š, or MN-alu-
miniumoxide (neutral) with 0.3–0.5 bar pressure.
UV/Vis spectra were recorded in VARIAN Cary 50 UV/Vis spectrome-
ter equipped with thermostated sell holder with a magnetic stirrer under-
neath. The data is reported as l (e) in the units of nm (mÀ1 cmÀ1). The
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Chem. Eur. J. 2007, 13, 2671 –2685

Photochromism
FULL PAPER
forms isolated were then warmed up to room temperature, and was kept
in dark till complete fading of the color (if some residue color of TT or
closed-TT remains, it could be bleached by irradiation with visible light).
The regenerated absorption spectrum of bisnaphthopyran 1a–c, f, 2 f, and
i was compared with standard solution of 1a–c, f, 2 f, and i so that the
concentration of the colored from isolated could be obtained and the ex-
tinction coefficient of the isolated colored form (converted to the value
at room temperature) could be calculated according to Lambert–Beer
law.
7.65 (dd, J=3.7, 1.2 Hz, 1H), 7.63–7.55 (m, 1H), 7.54–7.46 (m, 2H),
7.17 ppm (dd, J=5.0, 3.7 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=187.9,
143.5, 138.0, 134.7, 134.0, 132.1, 129.0, 128.3, 127.8 ppm; IR (CHCl3): n˜ =
3023, 3013, 1637, 1600, 1515, 1448, 1414, 1354, 1290, 1232, 1053, 844, 758,
721 cmÀ1
;
p-Methylphenyl thiophene-2-yl ketone (4d): The general procedure was
followed and the reaction was performed at 238C for 3 h. Pale-pink solid
1
was obtained in yield of 92.6%. M.p. 75.0–75.68C (lit.[30] 768C); H NMR
(300 MHz, CDCl3): d=7.82–7.76 (m, 2H), 7.70(dd, J=5.0, 1.3 Hz, 1H),
7.65 (d, J=3.7, 1.3 Hz, 1H), 7.33–7.27 (m, 2H), 7.16 (dd, J=5.0, 3.7 Hz,
1H), 2.45 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d=187.9, 143.8,
143.0, 135.4, 134.4, 133.8, 129.3, 129.0, 127.8, 21.6 ppm; IR (CHCl3): n˜ =
Photocoloration and quantum yield measurements: Photocoloration ki-
netic measurements were carried out in thermostated cuvette irradiated
with UV (366 nm) from 150 W medium pressure Hg lamp filtered
through the combination of yfc6 and C3C23 optical filters and was fo-
cused with quartz lenses using 5.0”10À5 m solution of photochromic com-
pound in CH2Cl2. Irradiation beam of UV is at 908 angle to the monitor-
ing beam and the absorbance was monitored at the absorption maximum
of the colored form with Cary 50 UV/Vis spectrometer. The light intensi-
ty was measured with potassium ferrioxalate actinometer following stan-
dard procedure.[22]
Thermofading kinetic measurements: 5.0”10À5 m solution of photochro-
mic compound in CH2Cl2 in thermostated cuvette was irradiated for 5 s
with UV (366 nm). Once the light source was removed, the absorbance
at the absorption maximum of the colored form was monitored with
Cary 50. The temperature was controlled with thermocryostat to be
287.4 K.
3023, 3013, 1631, 1606, 1514, 1415, 1354, 1312, 1297, 850, 722 cmÀ1
.
p-Methoxyphenyl thiophene-2-yl ketone (4e): The general procedure was
followed and the reaction was performed at 238C for 5 h. Colorless crys-
tals were obtained in yield of 98.0%. M.p. 74–758C (lit.[31] 73.5–748C);
1H NMR (300 MHz, CDCl3): d=7.94–7.87 (m, 4H), 7.69 (dd, J=5.0,
1.2 Hz, 1H), 7.65 (dd, J=3.7, 1.2 Hz, 1H), 7.16 (dd, J=5.0, 3.7 Hz, 1H),
7.02–6.92 (m, 4H), 3.90 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d=
186.6, 162.9, 143.7, 133.9, 133.3, 131.5, 130.6, 127.6, 113.6, 55.5 ppm; IR
(CHCl3): n˜ =3019, 2868, 2842, 1630, 1600, 1509, 1414, 1354, 1311, 1292,
1259, 1210, 1175, 1031, 856, 849, 758 cmÀ1
.
General procedure for preparation of 2,2’-bithiophene-5-yl ketone: Tin
tetrachloride (12 mmol) was added dropwise under nitrogen with stirring
to a solution of bithiophene (12 mmol) and (substituted) benzoyl chloride
(16 mmol) in CH2Cl2 (90 mL) below 48C. After addition, the reaction
mixture was stirred at room temperature, poured onto mixture of crushed
ice (100 g) and 5m HCl (5 mL). The organic layer was separated and the
aqueous layer was extracted with CH2Cl2 (15 mL). The combined organic
solution was passed through a short silica gel column (CH2Cl2/ethyl ace-
tate 10:1). Solvent was removed, the residue was recrystallized from
CH2Cl2/hexane.
Fatigue-resistance measurements: A stirred solution of photochromic
compound in toluene was equilibrated in a thermostated cuvette for 0.5 h
prior to photoirradiation. It was irradiated for 4 min with white light
from 150 W Xenon lamp which was passed through a water circulated
heat trap and C3C26 optical filter to eliminate heat, infrared light, and
UV light less than 300 nm, then the absorbance was started to be moni-
tored with Cary 50. The output of the white light was measured with
EPM-1000 power meter.
2,2’-Bithiophene-5-yl o-fluorophenyl ketone (4 f): The general procedure
was followed and the reaction was performed at 48C for 40 min followed
by 238C for 1 h. Yellow-green crystals were obtained in yield of 44.5%.
M.p. 81.4–82.08C; 1H NMR (300 MHz, CDCl3): d=7.63–7.47 (m, 2H),
7.43 (dd, J=4.1, 1.9 Hz, 1H), 7.40–7.31 (m, 2H), 7.30–7.12 (m, 3H),
7.08 ppm (dd, J=5.3, 3.7 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=184.6,
159.7 (1J=252.7 Hz), 147.3, 141.9, 136.4, 136.3, 132.9 (3J=8.6 Hz), 130.3
(3J=3.4 Hz), 128.4, 126.9, 126.0, 124.3, 124.3 (4J=4.9 Hz), 116.5 ppm
(2J=22.0 Hz); IR (CHCl3): n˜ =3078, 3020, 3013, 1637, 1613, 1508, 1485,
General procedure for preparation of thienyl ketone: Tin tetrachloride
(20.84 g, 80 mmol) was added dropwise under nitrogen with stirring to
ice-cooled solution of thiophene (6.5 g, 77 mmol) and (substituted) ben-
zoyl chloride (80 mmol) in CH2Cl2 (90 mL) over 20 min. After addition,
the reaction mixture was stirred for further 10 min, then stirred at room
temperature for 2.5–5 h before pouring onto mixture of crushed ice
(200 g) and 5m HCl (10 mL). The organic layer was separated and the
aqueous layer was extracted with CH2Cl2 (15 mL). The combined organic
solutions were concentrated to remove most of the solvent. The residue
was filtered through a plug of silica gel and washed with CH2Cl2. After
removal of solvent, the residue was recrystallized from CH2Cl2/hexane.
Solid was collected by filtration. The mother liquid was decolored with
charcoal and recrystallized from CH2Cl2/hexane.
1445, 1422, 1314, 1315, 1228, 1058, 875, 815, 757, 703 cmÀ1
.
2,2’-Bithiophene-5-yl naphthalene-2-yl ketone (4g): The general proce-
dure was followed and the reaction was performed 238C for 2 h. Yellow
solid was obtained in yield of 62.0%. M.p. 139.3–139.98C; 1H NMR
(300 MHz, CDCl3): d=8.40 (s, 1H), 8.02–7.88 (m, 4H), 7.63 (d, J=
4.0 Hz, 1H), 7.66–7.54 (m, 2H), 7.38 (dd, J=3.7, 1.2 Hz, 1H), 7.36 (dd,
J=5.3, 1.2 Hz, 1H), 7.25 (d, J=3.7 Hz, 1H), 7.09 ppm (dd, J=5.3,
3.7 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=187.4, 146.0, 141.6, 136.2,
135.7, 135.1, 135.0, 132.2, 130.1, 129.1, 128.3, 128.2, 128.0, 127.7, 126.7,
126.5, 125.7, 125.1, 124.0 ppm; IR (CHCl3): n˜ =3063, 3026, 3012, 1625,
1507, 1466, 1447, 1422, 1354, 1311, 1297, 1236, 1226, 1058, 810, 794, 722,
o-Fluorophenyl thiophene-2-yl ketone (4a): The general procedure was
followed and the reaction was performed at 238C for 4 h. Brown oil was
obtained in yield of 98.0%. 1H NMR (300 MHz, CDCl3): d = 7.75 (dd,
J=5.0, 1.2 Hz, 1H), 7.62–7.48 (m, 3H), 7.27 (td, J=7.4, 1.3 Hz, 1H),
7.23–7.15 (m, 1H), 7.14 ppm (dd, J=5.0, 4.0 Hz, 1H); 13C NMR (CDCl3):
d=184.8, 159.4 (1J=252.1 Hz), 143.9, 135.3 (5J=2.4 Hz), 135.1, 132.7
(3J=7.9 Hz), 130.0 (3J=3.1 Hz), 127.0 (2J=15.3 Hz), 124.0 (4J=3.1 Hz),
116.3 ppm (2J=22.0 Hz); IR (CHCl3): n˜ =3020, 1644, 1613, 1516, 1486,
702 cmÀ1
.
2,2’-Bithiophene-5-yl p-Methoxyphenyl ketone (4h): The general proce-
dure was followed and the reaction was performed at 238C for 20 min.
Yellow-green crystals were obtained in yield of 67.7%. M.p. 119.0–
119.68C (lit.[16] 119–1208C); 1H NMR (300 MHz, CDCl3): d=7.94–7.86
(m, 4H), 7.55 (d, J=4.0 Hz, 1H), 7.35 (dd, J=3.7, 0.9 Hz, 1H), 7.33 (dd,
J=5.3, 1.2 Hz, 1H), 7.21 (d, J=3.7 Hz, 1H), 6.97 (dd, J=5.3, 3.7 Hz,
1H), 7.03–6.96 (m, 4H), 3.90 ppm (s, 3H); 13C NMR (75 MHz, CDCl3):
d=186.2, 162.8, 145.3, 141.7, 136.3, 134.8, 131.3, 130.4, 128.1, 126.3, 125.5,
123.9, 113.6, 95.6, 55.5 ppm; IR (CHCl3): n˜ =3076, 3013, 2967, 2842, 1624,
1600, 1573, 1506, 1447, 1423, 1315, 1293, 1259, 1214, 1175, 1058, 1131,
1452, 1412, 1356, 1305, 1286, 1228, 1053, 889, 854, 769, 753 cmÀ1
.
p-Fluorophenyl thiophene-2-yl ketone (4b): The general procedure was
followed and the reaction was performed at 238C for 2.5 h. Pale-pink
solid was obtained in yield of 91.1%. M.p. 96.8–97.58C (lit.[28] 98–998C);
1H NMR (200 MHz, CDCl3): d=7.97–7.84 (m, 2H), 7.73 (dd, J=5.0,
1.3 Hz, 1H), 7.63 (dd, J=3.7, 0.8 Hz, 1H), 7.25–7.10 (m, 3H), 2.99 (s,
1H), 2.90 ppm (s, 1H); 13C NMR (CDCl3): d=186.7, 162.5 (1J=
253.8 Hz), 143.3, 134.6, 134.3, 134.3, 131.7 (3J=9.6 Hz), 128.0, 115.6 ppm
(2J=21.3 Hz); IR (CHCl3): n˜ =3025, 3018, 1638, 1600, 1505, 1416, 1354,
1300, 1287, 1241, 1232, 1157, 1053, 858, 758 cmÀ1
.
869, 844, 810, 701 cmÀ1
.
Phenyl thiophene-2-yl ketone (4c): The general procedure was followed
and the reaction was performed at 238C for 4 h. White solid was ob-
tained in yield of 89.6%. M.p. 52.0–52.68C (lit.[29] 48–508C); 1H NMR
(300 MHz, CDCl3): d=7.90–7.82 (m, 4H), 7.73 (dd, J=5.0, 1.2 Hz, 1H),
2,2’-Bithiophene-5-yl p-fluorophenyl ketone (4i): The general procedure
was followed and the reaction was performed at 238C for 70 min. Yellow
solid was obtained in yield of 57.8%. M.p. 115.3–115.88C; 1H NMR
(300 MHz, CDCl3): d=7.96–7.82 (m, 2H), 7.53 (d, J=3.4 Hz, 1H), 7.40–
Chem. Eur. J. 2007, 13, 2671 –2685
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2681

E. M. Carreira and W. Zhao
7.30 (m, 2H), 7.24–7.11 (m, 3H), 7.08 ppm (dd, J=5.0, 3.7 Hz, 1H);
13C NMR (75 MHz, CDCl3): d=186.4, 165.4 (1J=253.9 Hz), 146.5, 141.4,
136.3, 134.4, 131.7, 131.6 (3J=8.5 Hz), 128.4, 126.8, 125.9, 124.2,
115.7 ppm (2J=22.0 Hz).
55.3 ppm; IR (CHCl3): n˜ =3582, 3306, 3020, 2960, 2840, 2119, 1608, 1585,
1510, 1464, 1304, 1252, 1176, 1036, 972, 959, 832, 706 cmÀ1
.
1-(2,2’-Bithiophene-5-yl)-1-(o-fluorophenyl)prop-2-yn-1-ol (5 f): The gen-
eral procedure was followed using 2.2 equiv of sodium acetylide as base
and yellow-brown oil was obtained in yield of 82.7%. 1H NMR
(300 MHz, CDCl3): d=7.75 (td, J=8.1, 1.9 Hz, 1H), 7.41–7.31 (m, 1H),
1-Phenyl-1-(thiophene-2-yl)-prop-2-yn-1-ol (5c): Lithium acetylide dia-
mine complex (15 mmol) in dry DMSO (25 mL) was added to p-aromatic
ketone (15 mmol) in portions with stirring over 20 min. After addition,
the reaction mixture was stirred at room temperature for 2 h, poured
onto crushed ice, CH2Cl2 (30 mL) was added, filtered through Celite, ex-
tracted with CH2Cl2. The mixture was dried over anhydrous sodium sul-
fate, filtered, and purified by flush chromatography (silica gel, hexane/
CH2Cl2 1:2). Evaporation of the solvent gave yellow oil in yield of
7.24–7.16(m, 2H), 7.13 (dd, J=3.4, 1.2 Hz, 1H), 7.10 (ddd, J=11.6, 3.4,
H
1.2 Hz, 1H), 7.05 (d, J=3.7 Hz, 1H), 7.00 (d, J=3.7 Hz, 1H), 6.99 (dd,
J=5.0, 3.4 Hz, 1H), 3.31 (s, 1H), 3.30 (s, 1H), 2.90 (s, 1H), 2.89 ppm (s,
1H); 13C NMR (75 MHz, CDCl3): d=160.0 (1J=248.1 Hz), 146.4, 138.2,
137.0, 130.4 (3J=8.6 Hz), 130.4 (2J=6.3 Hz), 127.8, 127.1 (2J=1.5 Hz),
126.3, 124.6, 124.0 (4J=3.7 Hz), 124.0, 122.9, 116.3 (2J=20.6 Hz), 83.8,
69.0 ppm; IR (CHCl3): n˜ =3025, 3018, 1638, 1600, 1505, 1416, 1354, 1300,
1
76.8%. H NMR (300 MHz, CDCl3): d=7.73–7.68 (m, 2H), 7.42–7.29 (m,
3H), 7.27 (dd, J=5.0, 1.2 Hz, 1H), 7.09 (dd, J=3.7, 1.2 Hz, 1H), 6.92
(dd, J=5.0, 3.7 Hz, 1H), 3.02 (s, 1H), 2.99 ppm (s, 1H); 13C NMR
(75 MHz, CDCl3): d=149.3, 143.5, 128.2, 128.1, 126.3, 126.0, 125.6, 125.5,
85.7, 74.9, 71.7 ppm; IR (CHCl3): n˜ =3582, 3306, 3068, 3029, 3013, 2119,
1601, 1491, 1450, 1434, 1353, 1324, 1234, 1180, 1160, 1031, 973, 958, 834,
1287, 1241, 1232, 1157, 1053, 858, 758 cmÀ1
.
1-(2,2’-Bithiophene-5-yl)-1-(naphthalene-2-yl)prop-2-yn-1-ol (5g): The
general procedure was followed using 2.0 equiv of sodium acetylide as
base and yellow-brown oil was obtained in yield of 86.6%. 1H NMR
(300 MHz, CDCl3): d=8.25 (d, J=1.9 Hz, 1H), 7.96–7.80 (m, 3H), 7.74
(dd, J=8.7, 1.9 Hz, 1H), 7.58–7.46 (m, 2H), 7.19 (dd, J=5.3, 1.2 Hz,
1H), 7.11 (dd, J=3.7, 1.2 Hz, 1H), 7.04 (d, J=3.7 Hz, 1H), 7.01–6.92 (m,
2H), 3.08 (s 1H), 2.97 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=
147.8, 140.3, 138.2, 136.8, 132.9, 132.9, 128.4, 128.2, 127.6, 127.5, 126.4,
126.2, 124.5, 124.0, 123.9, 123.7, 122.8, 85.2, 75.4, 71.7 ppm; IR (CHCl3):
n˜ =3580, 3305, 3062, 3012, 2958, 2929, 2118, 1601, 1508, 1466, 1425, 1356,
701 cmÀ1
.
General procedure for preparation of propargyl alcohol: Sodium acety-
lide (1.4–2.2 equiv) suspended in dry DMSO (25 mL) was added aromatic
ketone (25 mmol) in portions with stirring over 20 min under water bath
cooling while bubbling acetylene gas. After addition, the reaction mixture
was stirred at room temperature for 2 h, poured onto crushed ice, acidi-
fied with 4m HCl until the pH was approximately 6. After extraction
with CH2Cl2 (20 mL, then 2”10 mL), the mixture was dried over anhy-
drous sodium sulfate and filtered. Evaporation of the solvent, the result-
ed oil was purified by flush chromatography on neutral alumina (activity
III) (hexane/CH2Cl2 2:1).
1315, 1270, 1228, 1119, 1037, 979, 942, 894, 858, 820, 798, 698 cmÀ1
.
1-(2,2’-Bithiophene-5-yl)-1-(p-methoxyphenyl)prop-2-yn-1-ol (5h): The
general procedure was followed using 1.68 equiv of sodium acetylide as
base and yellow-brown oil was obtained in yield of 71.0%. 1H NMR
(300 MHz, CDCl3): d=7.67–7.60 (m, 2H), 7.19 (dd, J=5.0, 1.2 Hz, 1H),
7.12 (dd, J=3.7, 1.2 Hz, 1H), 7.01–6.95 (m, 3H), 7.94–7.87 (m, 2H), 3.82
(s, 3H), 3.03 (s, 1H), 2.90 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=
159.4, 148.3, 137.9, 137.0, 135.4, 127.6, 127.0, 125.9, 124.5, 123.7, 113.5,
85.5, 75.0, 71.4, 55.3 ppm; IR (CHCl3): n˜ =3581, 3305, 3076, 3020, 3012,
2960, 2840, 2118, 1608, 1585, 1510, 1465, 1304, 1253, 1176, 1036, 973, 957,
1-(o-Fluorophenyl)-1-(thiophene-2-yl)-prop-2-yn-1-ol (5a): The general
procedure was followed using 1.5 equiv of sodium acetylide as base and
yellow-brown oil was obtained in yield of 60.2%. 1H NMR (300 MHz,
CDCl3): d=7.70 (td, J=8.1, 1.9 Hz, 1H), 7.40–7.30 (m, 1H), 7.30 (dd, J=
5.4, 1.3 Hz, 1H), 7.17 (td, J=7.8, 1.3 Hz, 1H), 7.14 (ddd, J=3.7, 1.3,
0.6 Hz, 1H), 7.04 (dd, J=11.5, 8.1, 1.3 Hz, 1H), 6.95 (dd, J=5.0, 3.4 Hz,
1H), 3.26 (d, J=3.4 Hz, 1H), 2.87 ppm (d, J=0.9 Hz, 1H); 13C NMR
(75 MHz, CDCl3): d=159.8 (1J=248.4 Hz), 147.6, 130.6 (2J=9.4 Hz),
130.2 (3J=8.5 Hz), 127.0 (3J=1.8 Hz), 126.4, 126.1, 125.7, 123.8 (4J=
3.0 Hz), 116.2 (1J=21.4 Hz), 84.1, 74.5 (5J=2.2 Hz), 69.0 ppm; IR
(CHCl3): n˜ =3586, 3306, 3080, 3068, 3030, 3013, 2123, 1614, 1586, 1488,
829, 805, 698 cmÀ1
.
1-(2,2’-Bithiophene-5-yl)-1-(p-fluorophenyl)prop-2-yn-1-ol (5i): The gen-
eral procedure was followed using 2.2 equiv of sodium acetylide as base
and yellow-brown oil was obtained in yield of 82.7%. 1H NMR
(300 MHz, CDCl3): d=7.74–7.65 (m, 2H), 7.21 (dd, J=5.0, 1.2 Hz, 1H),
7.12 (dd, J=3.7, 1.2 Hz, 1H), 7.11–7.02 (m, 2H), 7.02–6.96 (m, 3H), 3.04
(s, 1H), 2.92 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=162.5 (1J=
247.8 Hz), 147.9, 139.2, 138.4, 127.8, 127.6 (3J=8.5 Hz), 126.2, 124.7,
123.9, 122.9, 115.2 (2J=22.0 Hz), 85.1, 75.3, 71.2 ppm.
1453, 1354, 1332, 1273, 1230, 1179, 1151, 1026, 973, 839, 706 cmÀ1
.
1-(p-Fluorophenyl)-1-(thiophene-2-yl)-prop-2-yn-1-ol (5b): The general
procedure was followed using 1.5 equiv of sodium acetylide as base and
yellow-brown oil was obtained in yield of 82.4%. 1H NMR (200 MHz,
CDCl3): d=7.73–7.61 (m, 2H), 7.28 (dd, J=5.0, 1.3 Hz, 1H), 7.09 (dd,
J=3.7, 1.3 Hz, 1H), 7.10–6.98 (m, 2H), 6.93 (dd, J=5.0, 3.7 Hz, 1H),
2.99 (s, 1H), 2.90 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=162.7
(1J=246.6 Hz), 149.5, 139.6 (4J=2.6 Hz), 127.7 (3J=7.6 Hz), 126.6, 126.4,
125.7, 115.2 (2J=22.0 Hz), 85.5, 75.1, 71.2 ppm; IR (CHCl3): n˜ =3582,
3305, 3078, 3020, 2120, 1604, 1508, 1410, 1354, 1322, 1234, 1209, 1160,
General procedure for preparation of naphthopyran 2: Propargyl alcohol
5 (1.05 mmol) and 2-naphthol (144.2 mg, 1 mmol) in the presence of
PPTS (12.6 mg, 0.05 mmol) and trimethyl orthoformate (0.21 mL,
2 mmol) in 1,2-dichloroethane (2 mL) was refluxed for 2 h or stirred at
238C for 3–4.5 h followed by 0.5–1 h reflux. Solvent was removed in
vacuo and the residue was purified by chromatography (silica gel,
CH2Cl2/hexane 2:1), and recrystallization from CH2Cl2/hexane (or dried
under high vacuum).
1035, 975, 959, 837, 706 cmÀ1
.
1-(p-Methylphenyl)-1-(thiophene-2-yl)-prop-2-yn-1-ol (5d): The general
procedure was followed using 1.5 equiv of sodium acetylide as base and
yellow-brown oil was obtained in yield of 86.6%. 1H NMR (200 MHz,
CDCl3): d=7.62–7.53 (m, 2H), 7.26(dd, J=5.0, 1.2 Hz, 1H), 7.23–7.13 (m,
2H), 7.10 (dd, J=3.7, 1.2 Hz, 1H), 6.92 (dd, J=5.0, 3.7 Hz, 1H), 2.96 (s,
1H), 2.88 (s, 1H), 2.36 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d=
149.8, 141.0, 138.2, 129.0, 126.5, 126.1, 125.7, 125.6, 85.8, 74.8, 71.6,
21.0 ppm; IR (CHCl3): n˜ =3582, 3306, 3068, 3020, 3012, 2925, 2868, 2119,
1611, 1511, 1434, 1353, 1323, 1234, 1182, 1035, 972, 960, 845, 837, 812,
3-(o-Fluorophenyl-3-(thiophene-2-yl)-[3H]-naphtho
[2,1-b]pyran
(2a):
The general procedure was followed and the reaction was performed
under reflux for 2 h, pale-yellow solid was obtained in yield of 88.8%.
M.p. 118–118.58C (lit.[11] 1168C); 1H NMR (300 MHz, CDCl3): d=7.97
(d, J=8.3 Hz, 1H), 7.76 (td, J=8.1, 1.9 Hz, 1H), 7.74 (d, J=8.1 Hz, 1H),
7.70 (d, J=9.0 Hz, 1H), 7.49 (ddd, J=8.4, 6.9, 1.6 Hz, 1H), 7.35 (ddd, J=
8.1, 6.9, 1.2 Hz, 1H), 7.33–7.20 (m, 4H), 7.14 (td, J=7.5, 1.2 Hz, 1H),
7.04 (ddd, J=11.5, 8.1, 1.2 Hz, 1H), 7.01–6.96 (m, 1H), 6.92 (dd, J=5.0,
3.4 Hz, 1H), 6.50 ppm (dd, J=10.0, 4.7 Hz, 1H); 13C NMR (75 MHz,
CDCl3): d=159.5 (1J=249.0 Hz), 150.1, 148.1, 131.2 (2J=11.0 Hz), 130.0
(3J=11.0 Hz), 129.8, 129.6, 128.6, 127.6 (3J=3.7 Hz), 126.8, 126.5, 126.4,
126.2, 125.8 (5J=3.7 Hz), 123.9, 123.9 (4J=3.7 Hz), 121.4, 119.8, 118.2,
116.5 (2J=23.2 Hz), 113.8, 78.2 ppm (3J=2.6 Hz); UV (toluene): lmax (e)
= 306sh (20700), 317 (23400 molÀ1 dm3 cmÀ1); IR (KBr): n˜ =3062, 1632,
1602, 1584, 1504, 1460, 1224, 1205, 1177, 1159, 1086, 1003, 952, 825, 814,
749, 725, 696 cmÀ1; HRMS (MALDI): m/z (%): calcd for C23H15FOS:
359.0911; found: 359.0914 (100) [M+H+].
706 cmÀ1
.
1-(p-Methoxyphenyl)-1-(thiophene-2-yl)-prop-2-yn-1-ol (5e): The general
procedure was followed using 2.0 equiv of sodium acetylide as base and
brown oil was obtained in yield of 84.1%. 1H NMR (300 MHz, CDCl3):
d=7.64–7.57 (m, 2H), 7.26 (dd, J=5.0, 1.2 Hz, 1H), 7.08 (dd, J=3.7,
1.2 Hz, 1H), 6.92 (dd, J=5.0, 3.7 Hz, 1H), 6.91–6.85 (m, 2H), 3.81 (s,
3H), 2.93 (s, 1H), 2.88 ppm (s, 1H); 13C NMR (75 MHz, CDCl3): d=
159.2, 149.6, 135.8, 127.0, 126.3, 125.9, 125.3, 113.4, 85.8, 74.8, 71.4,
2682
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Chem. Eur. J. 2007, 13, 2671 –2685

Photochromism
FULL PAPER
3-(p-Fluorophenyl-3-(thiophene-2-yl)-[3H]-naphtho
N
(2b):
J=5.0, 1.2 Hz, 1H), 7.09 (dd, J=3.7, 1.2 Hz, 1H), 6.97 (d, J=3.7 Hz,
1H), 6.96 (dd, J=5.0, 3.7 Hz, 1H), 6.92–6.85 (m, 2H), 6.84 (d, J=3.7 Hz,
1H), 6.25 (d, J=9.7 Hz, 1H), 3.79 ppm (s, 3H); 13C NMR (75 MHz,
CDCl3): d=159.4, 150.4, 148.6, 138.3, 137.4, 136.3, 130.1, 129.9, 129.6,
128.6, 127.8, 127.1, 127.0, 126.8, 124.5, 123.8, 122.9, 121.4, 119.9, 118.4,
113.9, 113.5, 80.2, 55.2 ppm; IR (KBr): n˜ =3060, 2952, 2930, 2833, 1633,
1607, 1584, 1509, 1460, 1438, 1251, 1203, 1175, 1083, 1034, 999, 806, 746,
695 cmÀ1; HRMS (MALDI): m/z (%): calcd for C28H20O2S2: 453.0977;
found: 453.0976 (100) [M+H+].
The general procedure was followed and the reaction was performed
under reflux for 2 h, colorless solid was obtained in yield of 98.2%. M.p.
122.5–1248C; 1H NMR (300 MHz, CDCl3): d=7.97 (d, J=8.4 Hz, 1H),
7.73 (d, J=8.1 Hz, 1H), 7.68 (d, J=9.0 Hz, 1H), 7.60–7.51 (m, 2H), 7.49
(ddd, J=8.4, 7.2, 1.2 Hz, 1H), 7.34 (ddd, J=8.1, 6.8, 1.2 Hz, 1H), 7.32 (d,
J=9.7 Hz, 1H), 7.29 (dd, J=5.0, 1.6 Hz, 1H), 7.19 (d, J=8.7 Hz, 1H),
7.08–6.88 (m, 4H), 6.25 ppm (d, J=10.0 Hz, 1H); 13C NMR (75 MHz,
CDCl3): d=162.4 (1J=246.6 Hz), 150.3, 149.3, 140.4, 130.2, 129.8, 129.6,
128.7, 128.4 (3J=7.3 Hz), 127.1, 126.9, 126.5, 123.9, 121.3, 120.0, 118.3,
115.0 (2J=20.8 Hz), 113.9, 80.0 ppm; IR (KBr): n˜ =3062, 1632, 1602,
1585, 1504, 1461, 1224, 1206, 1177, 1159, 1086, 1003, 952, 825, 814, 749,
3-(2,2’-Bithiophene-5-yl)-3-(p-fluorophenyl)-[3H]-naphtho[2,1-b]pyran
G
(2i): The general procedure was followed and the reaction was performed
at 238C for 4.5 h followed by 1 h reflux, beige solid was obtained in yield
of 94.5%. M.p. 155.5–156.38C; 1H NMR (300 MHz, CDCl3): d=7.98 (d,
J=8.7 Hz, 1H), 7.74 (d, J=8.1 Hz, 1H), 7.69 (d, J=8.7 Hz, 1H), 7.63–
7.54 (m, 2H), 7.50 (ddd, J=8.4, 6.9, 1.2 Hz, 1H), 7.35 (ddd, J=8.1, 6.8,
0.9 Hz, 1H), 7.34 (d, J=10.0 Hz, 1H), 7.20 (d, J=10.0 Hz, 1H), 7.17 (dd,
J=5.3, 0.9 Hz, 1H), 7.10 (dd, J=3.4, 0.9 Hz, 1H), 7.09–6.99 (m, 2H),
6.97 (dd, J=5.0, 3.7 Hz, 1H), 6.96 (d, J=3.7 Hz, 1H), 6.84 (d, J=4.0 Hz,
1H), 6.23 ppm (d, J=10.0 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=
162.5 (1J=246.6 Hz), 150.2, 148.0, 140.0, 138.6, 137.2, 130.3, 129.9, 129.7,
128.7, 128.4 (3J=8.5 Hz), 127.8, 127.2, 126.9, 126.7, 124.7, 123.9, 122.9,
121.4, 120.3, 118.3, 115.1 (2J=22.0 Hz), 113.9, 80.0 ppm; IR (KBr): n˜ =
3070, 1632, 1603, 1584, 1503, 1459, 1231, 1209, 1157, 1084, 1046, 986, 828,
815, 796, 748, 692 cmÀ1; UV (toluene): lmax (e) = 306sh (21000), 317
(23600 molÀ1 dm3 cmÀ1); HRMS (MALDI): m/z (%): calcd for
C27H17FOS2: 441.0778; found: 441.0774 (100) [M+H+].
726, 696 cmÀ1
; HRMS (MALDI): m/z (%): calcd for C23H15FOS:
359.0911; found: 359.0913 (100) [M+H+].
3-(p-Methylphenyl)-3-(thiophene-2-yl)-[3H]-naphtho[2,1-b]pyran (2d):
The general procedure was followed and the reaction was performed
under reflux for 2 h, white solid was obtained in yield of 95.3%. M.p.
159.2–159.68C; 1H NMR (300 MHz, CDCl3): d=7.96 (d, J=8.4 Hz, 1H),
7.72 (dd, J=8.1, 0.6 Hz, 1H), 7.67 (d, J=8.7 Hz, 1H), 7.51–7.43 (m, 3H),
7.32 (ddd, J=8.1, 6.8, 0.9 Hz, 1H), 7.32–7.26 (m, 2H), 7.20 (d, J=8.7 Hz,
1H), 7.18–7.10 (m, 2H), 6.95 (dd, J=3.4, 1.2 Hz, 1H), 6.91 (dd, J=5.0,
3.4 Hz, 1H), 6.28 (d, J=10.0 Hz, 1H), 2.33 ppm (s, 3H); 13C NMR
(75 MHz, CDCl3): d=150.3, 149.5, 141.5, 137.5, 129.9, 129.7, 129.4, 128.7,
128.5, 126.1, 127.4, 126.6, 126.3, 123.6, 121.3, 119.6, 118.3, 113.8, 80.2,
21.1 ppm; IR (KBr): n˜ =3084, 3022, 2918, 1634, 1510, 1461, 1435, 1244,
1236, 1104, 1091, 1005, 808, 751, 711 cmÀ1; HRMS (MALDI): m/z (%):
calcd for C24H18OS: 355.1162; found: 355.1164 (100) [M+H+].
General procedure for preparation of bispyran 1: Butyl lithium (1.6m,
0.5 mL, 0.8 mmol) was added dropwise with stirring to a solution of
naphthopyran 2 (0.5 mmol) in dry THF (4 mL) at À788C under nitrogen.
The mixture was stirred for 0.5 h, anhydrous cupric chloride (1.6–
2.2 equiv) was added in one portion. Stirring was continued for 2 h then
slowly warm up to room temperature and stirred overnight. Crushed ice
(10 g) was added to the reaction mixture. After acidification with 4m
HCl until the pH was approximately 1, the mixture was extracted with
CH2Cl2 (25 mL, then 2”10 mL). The combined organic solution was
dried over anhydrous sodium sulfate. If any solid was suspended in
CH2Cl2, heating was applied to dissolve the solid, cooled to room temper-
ature and then dried. Subsequently, it was filtered and passed through a
short silica gel column washed with CH2Cl2. After removal of the most of
the solvent until the total volume was approximately 5 mL, the mixture
was heated to reflux, cooled down and allowed to stand at room temper-
ature. The resulting solid was filtered and washed with a small volume of
CH2Cl2. The solid was collected and purified by chromatography (silica
gel, hexane/CH2Cl2 1:1) and recrystallized from CH2Cl2/hexane.
3-(2,2’-Bithiophene-5-yl)-3-(o-fluorophenyl)-[3H]-naphtho[2,1-b]pyran
G
(2 f): The general procedure was followed and the reaction was per-
formed at 238C for 4 h followed by 1 h reflux, pale-purple foam was ob-
tained in yield of 89.2%. 1H NMR (300 MHz, CDCl3): d=8.00 (d, J=
8.1 Hz, 1H), 7.83 (td, J=8.1, 1.9 Hz, 1H), 7.76 (d, J=8.1 Hz, 1H), 7.73
(d, J=9.0 Hz, 1H), 7.50 (ddd, J=8.1, 6.9, 1.2 Hz, 1H), 7.41–7.26 (m,
4H), 7.18 (dd, J=5.0, 1.2 Hz, 1H), 7.17 (td, J=7.4, 1.2 Hz, 1H), 7.11 (dd,
J=3.7, 1.2 Hz, 1H), 7.08 (ddd, J=11.5, 8.1, 1.2 Hz, 1H), 6.99 (d, J=
3.7 Hz, 1H), 6.97 (dd, J=5.3, 3.7 Hz, 1H), 6.91 (d, J=3.7 Hz, 1H),
6.52 ppm (dd, J=10.0, 4.7 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=
159.5 (1J=250.3 Hz), 150.0, 146.8, 138.5, 137.3, 130.9 (2J=11.0 Hz), 130.2,
130.0 (3J=8.7 Hz), 129.8, 129.7, 128.6, 127.8, 127.6 (3J=2.4 Hz), 126.9,
126.8, 125.3 (5J=4.9 Hz), 124.6, 124.0, 123.9 (4J=3.5 Hz), 123.1, 121.4,
120.1, 118.2, 116.5 (1J=22.0 Hz), 113.8, 78.2 ppm (3J=2.3 Hz); IR (KBr):
n˜ =3065, 1634, 1582, 1515, 1483, 1460, 1449, 1272, 1230, 1204, 1082, 1002,
803, 759, 747, 694 cmÀ1; UV (CH2Cl2): lmax (e) = 306sh (20700), 317
(23300 molÀ1 dm3 cmÀ1); UV (toluene): lmax (e)
= 306sh (20000), 317
(22800 molÀ1 dm3 cmÀ1); HRMS (MALDI): m/z (%): calcd for
C27H17FOS2: 441.0778; found: 441.0774 (100) [M+H+].
5,5’-Bis[3-(o-fluorophenyl)-[3H]-naphtho[2,1-b]pyran-3-yl]-2,2’-bithio-
A
phene (1a): The general procedure was followed and 2.0 equiv of CuCl2
was used, pink solid was obtained in yield of 72.7%. M.p. 206–2078C;
1H NMR (300 MHz, CDCl3): d=7.96 (d, J=8.4 Hz, 2H), 7.76 (ddd, J=
9.7, 7.8, 1.9 Hz, 1H), 7.73 (d, J=7.8 Hz, 1H), 7.69 (d, J=9.0 Hz, 1H),
7.54–7.42 (m, 1H), 7.40–7.24 (m, 3H), 7.22 (d, J=8.7 Hz, 1H), 7.18–7.09
(m, 1H), 7.08–6.96 (m, 1H), 6.88 (d, J=3.7 Hz, 1H), 6.83 (d, J=3.7 Hz,
1H), 6.44 ppm (dd, J=10.0, 4.4 Hz, 1H); 13C NMR (75 MHz, CDCl3):
d=159.1 (1J=247.8 Hz), 149.7, 146.6, 138.0, 130.6 (2J=11.0 Hz), 130.0,
129.8 (3J=7.9 Hz), 129.6, 129.4, 128.4, 127.3 (3J=2.8 Hz), 126.7, 126.7,
125.1 (5J=4.3 Hz), 123.8, 123.8 (4J=3.3 Hz), 122.9, 121.2, 120.0, 118.0,
116.3 (2J=21.9 Hz), 113.6, 78.1 ppm (3J=2.5 Hz); IR (KBr): n˜ =3065,
2956, 1635, 1613, 1581, 1512, 1482, 1446, 1238, 1207, 1082, 987, 800,
748 cmÀ1; UV (CH2Cl2): lmax (e) = 306sh (26800), 318 (33800), 333sh
3-(2,2’-Bithiophene-5-yl)-3-(naphthalene-2-yl)-[3H]-naphtho[2,1-b]pyran
U
(2g): The general procedure was followed and the reaction was per-
formed at 238C for 3.5 h followed by 1 h reflux, yellow orange solid was
obtained in yield of 92.4%. M.p. 189–1908C; 1H NMR (300 MHz,
CDCl3): d=8.09 (d, J=1.8 Hz, 1H), 7.99 (d, J=8.4 Hz, 1H), 7.88–7.78
(m, 3H), 7.77–7.67 (m, 3H), 7.54–7.43 (m, 3H), 7.39 (d, J=9.7 Hz, 1H),
7.33 (ddd, J=8.1, 6.8, 1.2 Hz, 1H), 7.28 (d, J=8.3 Hz, 1H), 7.17 (dd, J=
5.0, 1.2 Hz, 1H), 7.09 (dd, J=3.7, 1.2 Hz, 1H), 6.97 (d, J=4.7 Hz, 1H),
6.96 (dd, J=5.0, 3.7 Hz, 1H), 6.89 (d, J=3.7 Hz, 1H), 6.36 ppm (d, J=
9.7 Hz, 1H); 13C NMR (75 MHz, CDCl3): d=150.4, 148.1, 141.3, 137.3,
133.0, 132.9, 130.3, 129.9, 129.6, 128.7, 128.6, 128.2, 127.8, 127.7, 127.4,
126.4, 126.3, 125.4, 124.6, 123.9, 123.0, 121.4, 120.4, 118.4, 114.0,
80.5 ppm; IR (KBr): n˜ =3101, 3053, 1629, 1586, 1512, 1461, 1426, 1240,
1203, 1182, 1085, 1035, 1010, 828, 806, 747, 693 cmÀ1; HRMS (MALDI):
m/z (%): calcd for C31H20OS2: 473.1028; found: 473.1028 (100) [M +].
(28100 molÀ1 dm3 cmÀ1); UV (toluene): lmax (e)
= 306sh (25700), 318
(32900), 333sh (28300 molÀ1 dm3 cmÀ1); HRMS (MALDI): m/z (%):
calcd for C46H28F2O2S2: 714.1493; found: 714.1496 (100) [M +].
3-(2,2’-Bithiophene-5-yl)-3-(p-methoxyphenyl)-[3H]-naphtho
G
5,5’-Bis[3-(p-fluorophenyl)-[3H]-naphtho[2,1-b]pyran-3-yl]-2,2’-bithio-
N
(2h): The general procedure was followed and the reaction was per-
formed at 238C for 3.5 h followed by 0.5 h reflux, light purple foam was
obtained in yield of 83.5%. 1H NMR (300 MHz, CDCl3): d=7.98 (d, J=
8.1 Hz, 1H), 7.73 (d, J=8.1 Hz, 1H), 7.68 (d, J=9.0 Hz, 1H), 7.57–7.50
(m, 2H), 7.48 (ddd, J=8.4, 6.8, 1.6 Hz, 1H), 7.34 (ddd, H=8.1, 6.8,
0.9 Hz, 1H), 7.32 (d, J=9.7 Hz, 1H), 7.20 (d, J=9.0 Hz, 1H), 7.17 (dd,
phene (1b): The general procedure was followed and 2.0 equiv of CuCl2
was used, beige solid was obtained in yield of 55.0%. M.p. 200–2018C;
1H NMR (300 MHz, CDCl3): d=7.96 (d, J=8.1 Hz, 1H), 7.73 (d, J=
7.8 Hz, 1H), 7.67 (d, J=8.7 Hz, 1H), 7.59–7.50 (m, 2H), 7.48 (ddd, J=
8.4, 6.9, 1.3 Hz, 1H), 7.34 (ddd, J=8.1, 7.2, 1.2 Hz, 1H), 7.32 (d, J=
10.3 Hz, 1H), 7.17 (d, J=8.7 Hz, 1H), 7.07–6.96 (m, 2H), 6.88 (d, J=
Chem. Eur. J. 2007, 13, 2671 –2685
ꢀ 2007 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
2683

E. M. Carreira and W. Zhao
3.7 Hz, 1H), 6.80 (d, J=3.7 Hz, 1H), 6.18 ppm (d, J=10.0 Hz, 1H);
13C NMR (75 MHz, CDCl3): d=162.5 (1J=247.8 Hz), 150.2, 148.2, 140.0
(4J=3.7 Hz), 138.3, 130.3, 129.8, 129.6, 128.7, 128.4 (3J=8.6 Hz), 127.2,
126.9, 126.7, 123.9, 123.0, 121.4, 120.3, 118.3, 115.1 (2J=22.0 Hz), 113.8,
80.0 ppm; IR (KBr): n˜ =3067, 1632, 1608, 1588, 1508, 1461, 1240, 1202,
1158, 1085, 1004, 834, 802, 751 cmÀ1; UV (CH2Cl2): lmax (e) = 306sh
(26200), 318 (33200), 333sh (28000 molÀ1 dm3 cmÀ1); UV (toluene): lmax
(e) = 306sh (26700), 318 (33800), 333sh (28400 molÀ1 dm3 cmÀ1); HRMS
(MALDI): m/z (%): calcd for C46H28F2O2S2: 714.1493; found: 714.1498
(100) [M +].
128.4, 127.4 (3J=2.4 Hz), 126.8, 126.7, 125.1 (5J=4.6 Hz), 124.3, 124.1,
123.8, 122.9, 121.3, 120.0, 118.0, 116.4 (2J=22.0 Hz), 113.6, 78.2 ppm (3J=
2.2 Hz); IR (KBr): n˜ =3063, 1632, 1583, 1515, 1484, 1450, 1275, 1230,
1203, 1083, 1005, 809, 794, 756 cmÀ1; UV (CH2Cl2): lmax (e)
=
304
(14300), 318 (17500), 366sh (28400), 407 (42500 molÀ1 dm3 cmÀ1); UV
(toluene): lmax (e)
= 304 (15500), 318 (17900), 366sh (27600), 407
(40400 molÀ1 dm3 cmÀ1); HRMS (MALDI): m/z (%): calcd for
C62H36F2O2S4: 879.1326; found: 879.1320 (100) [M+H+].
5,5’’’-Bis[3-(naphthalene-2-yl)-[3H]-naphtho[2,1-b]pyran-3-yl]-
G
[2,2’,5’,2’’,5’’,2’’’]-quaterthiophene (1g): The general procedure was fol-
lowed and 1.6 equiv of CuCl2 was used, yellow-green solid was obtained
in yield of 88.2%. M.p. 163–1658C; H NMR (300 MHz, CDCl3): d=8.08
5,5’-Bis[3-phenyl-3H]-naphtho[2,1-b]pyran-3-yl]-2,2’-bithiophene 1c: The
A
1
general procedure was followed and 2.0 equiv of CuCl2 was used, beige
solid was obtained in yield of 96.5%. M.p. 244–2458C; 1H NMR
(300 MHz, CDCl3): d=7.95 (d, J=8.4 Hz, 1H), 7.72 (d, J=8.4 Hz, 1H),
7.65 (d, J=9.0 Hz, 1H), 7.60–7.53 (m, 2H), 7.51–7.43 (m, 1H), 7.40–7.24
(m, 5H), 7.18 (d, J=8.7 Hz, 1H), 6.87 (d, J=3.7 Hz, 1H), 6.80 (d, J=
3.7 Hz, 1H), 6.23 ppm (d, J=10.0 Hz, 1H); 13C NMR (75 MHz, CDCl3):
d=150.1, 148.1, 143.9, 138.0, 129.9, 129.6, 129.4, 128.4, 128.0, 127.8, 127.1,
126.7, 126.6, 126.2, 123.6, 122.7, 121.2, 119.9, 118.2, 113.7, 80.3 ppm; IR
(KBr): n˜ =3061, 3026, 1630, 1588, 1515, 1460, 1446, 1244, 1215, 1202,
1088, 1004, 905, 806, 754, 729, 697 cmÀ1; UV (CH2Cl2): lmax (e) = 306sh
(22400), 318 (28500), 333sh (24100 molÀ1 dm3 cmÀ1); UV (toluene): lmax
(e) = 306sh (19800), 318 (25500), 333sh (21800 molÀ1 dm3 cmÀ1); HRMS
(MALDI): m/z (%): calcd for C46H30O2S2: 679.1760; found: 679.1752
(100) [M+H+].
(d, J=1.9 Hz, 1H), 7.99 (d, J=8.4 Hz, 1H), 7.88–7.78 (m, 3H), 7.76–7.64
(m, 3H), 7.54–7.42 (m, 3H), 7.38 (d, J=9.6 Hz, 1H), 7.37–7.30 (m, 1H),
7.27 (d, J=9.0 Hz, 1H), 7.02–6.94 (m, 2H), 6.95 (d, J=3.7 Hz, 1H), 6.88
(d, J=3.7 Hz, 1H), 6.35 ppm (d, J=10.0 Hz, 1H); 13C NMR (75 MHz,
CDCl3): d=150.2, 148.2, 141.1, 138.1, 136.1, 135.9, 132.8, 130.1, 129.7,
129.5, 128.5, 128.4, 128.1, 127.5, 127.4, 126.8, 126.6, 126.3, 126.3, 125.2,
124.4, 124.2, 123.8, 122.9, 121.3, 120.3, 118.3, 113.9, 80.4 ppm; IR (KBr):
n˜ =3059, 2951, 2920, 2867, 1631, 1587, 1514, 1459, 1460, 1437, 1239, 1182,
1084, 1008, 805, 799, 746 cmÀ1; UV (CH2Cl2): lmax (e) = 304 (17300), 318
(18600), 366sh (28700), 407 (42700 molÀ1 dm3 cmÀ1); UV (toluene): lmax
(e)
=
304
(17400),
318
(18700),
366sh
(28100),
407
(40800 molÀ1 dm3 cmÀ1); HRMS (MALDI): m/z (%): calcd for
C62H38O2S4: 942.1749; found: 942.1747 (100) [M +].
5,5’’’-Bis[3-(p-methoxyphenyl)-[3H]-naphtho[2,1-b]pyran-3-yl]-
[2,2’,5’,2’’,5’’,2’’’]-quaterthiophene (1h): The general procedure was fol-
A
5,5’-Bis[3-(p-methylphenyl)-[3H]-naphtho[2,1-b]pyran-3-yl]-2,2’-bithio-
A
phene (1d): The general procedure was followed and 2.0 equiv of CuCl2
was used, beige solid was obtained in yield of 77.1%. M.p. 206–2078C;
1H NMR (300 MHz, CDCl3): d=7.95 (d, J=8.1 Hz, 1H), 7.72 (d, J=
8.1 Hz, 1H), 7.65 (d, J=9.0 Hz, 1H), 7.42–7.52 (m, 3H), 7.32 (ddd, J=
8.1, 6.8, 0.9 Hz, 1H), 7.29 (d, J=9.7 Hz, 1H), 7.18 (d, J=8.7 Hz, 1H),
7.16–7.10 (m, 1H), 6.86 (d, J=3.7 Hz, 1H), 6.80 (d, J=3.7 Hz, 1H), 6.21
(d, J=10.0 Hz, 1H), 2.32 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d=
150.4, 148.6, 141.3, 138.2, 137.7, 130.1, 129.9, 129.6, 128.9, 128.6, 127.1,
127.0, 126.8, 126.4, 123.8, 122.9, 121.4, 119.9, 118.4, 113.9, 80.3, 21.0 ppm;
IR (KBr): n˜ =3059, 3024, 2919, 1632, 1588, 1513, 1461, 1444, 1243, 1222,
1201, 1086, 1003, 803, 749 cmÀ1; UV (CH2Cl2): lmax (e) = 306sh (26400),
lowed and 1.6 equiv of CuCl2 was used, yellow-green solid was obtained
1
in yield of 83.5%. M.p. 230–2318C; H NMR (300 MHz, CDCl3): d=7.98
(d, J=8.3 Hz, 1H), 7.73 (d, J=8.1 Hz, 1H), 7.68 (d, J=9.0 Hz, 1H),
7.58–7.42 (m, 2H), 7.38–7.31 (m 1H), 7.32 (d, J=10.0 Hz, 1H), 7.20 (d,
J=8.7 Hz, 1H), 7.01–6.95 (m, 1H), 6.95 (d, J=3.7 Hz, 1H), 6.93–6.84 (m,
2H), 6.84 (d, J=3.7 Hz, 1H), 6.24 (d, J=10.0 Hz, 1H), 3.79 ppm (s, 3H);
13C NMR (75 MHz, CDCl3): d=159.2, 150.2, 148.7, 137.8, 136.1, 136.1,
135.9, 130.0, 129.7, 129.5, 128.5, 127.8, 127.0, 126.9, 126.7, 124.3, 124.2,
123.7, 122.9, 121.3, 119.9, 118.3, 113.8, 113.5, 80.2, 55.3 ppm; IR (KBr):
n˜ =3059, 2956, 2930, 2834, 1629, 1606, 1584, 1508, 1460, 1440, 1255, 1217,
1171, 1081, 1030, 796, 745 cmÀ1; UV (CH2Cl2): lmax (e) = 304 (17300),
318 (18600), 366sh (28700), 407 (42700 molÀ1 dm3 cmÀ1); UV (toluene):
318 (33500), 333sh (28400 molÀ1 dm3 cmÀ1); UV (toluene): lmax (e)
=
306sh (27000), 318 (34800), 333sh (30000 molÀ1 dm3 cmÀ1); HRMS
(MALDI): m/z (%): calcd for C48H34O2S2: 706.1995; found: 706.1990
(100) [M +].
lmax (e)
=
304 (17400), 318 (18700), 366sh (28100), 407
(40800 molÀ1 dm3 cmÀ1); HRMS (MALDI): m/z (%): calcd for
C56H38O4S4: 902.1647; found: 902.1648 (100) [M +].
5,5’-Bis[3-(p-methoxyphenyl)-[3H]-naphtho[2,1-b]pyran-3-yl]-2,2’-bithio-
U
phene (1e): The general procedure was followed and 2.0 equiv of CuCl2
was used, beige solid was obtained in yield of 65.5%. M.p. 237–2388C;
1H NMR (300 MHz, CDCl3): d=7.95 (d, J=8.4 Hz, 1H), 7.71 (d, J=
8.5 Hz, 1H), 7.65 (d, J=9.0 Hz, 1H), 7.52–7.43 (m, 3H), 7.32 (ddd, J=
8.1, 6.8, 1.2 Hz, 1H), 7.29 (d, J=9.7 Hz, 1H), 7.16 (d, J=8.7 Hz, 1H),
6.88 (d, J=3.7 Hz, 1H), 6.88–6.82 (m, 2H), 6.79 (d, J=3.7 Hz, 1H), 6.20
(d, J=10.0 Hz, 1H), 3.78 ppm (s, 3H); 13C NMR (75 MHz, CDCl3): d=
159.2, 150.2, 148.5, 138.1, 136.1, 130.0, 129.7, 129.4, 128.5, 127.7, 127.0,
126.6, 123.7, 122.8, 121.3, 119.8, 118.3, 113.8, 113.4, 80.2, 55.2 ppm; IR
(KBr): n˜ =3055, 2952, 2838, 1631, 1609, 1586, 1510, 1461, 1439, 1256,
1241, 1177, 1084, 992, 827, 809 cmÀ1; UV (CH2Cl2): lmax (e) = 306sh
(26900), 318 (34200), 333sh (29200 molÀ1 dm3 cmÀ1); UV (toluene): lmax
(e) = 306sh (25700), 318 (33100), 333sh (28800 molÀ1 dm3 cmÀ1); HRMS
(MALDI): m/z (%): calcd for C48H34O4S2: 738.1893; found: 738.1893
(100) [M +].
Acknowledgements
This research was supported by the ETH-Z in the form of an INIT grant
and in part by a grant from the Swiss National Science Foundation.
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d) A. Osuka, D. Fujikane, H. Shinmor, S. Kobatake, M. Irie, J. Org.
Chem. 2001, 66, 3913–3923; e) T. Kaieda, S. Kobatake, H. Miyasaka,
M. Murakami, N. Iwai, Y. Nagata, A. Itaya, M. Irie, J. Am. Chem.
Soc. 2002, 124, 2015–2024; f) T. Kawai, T. Sasaki, M. Irie, Chem.
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Angew. Chem. 2003, 115, 3661–3664; Angew. Chem. Int. Ed. 2003,
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5,5’’’-Bis[3-(o-fluorophenyl)-[3H]-naphtho[2,1-b]pyran-3-yl]-
A
[2,2’,5’,2’’,5’’,2’’’]-quaterthiophene (1 f): The general procedure was fol-
lowed and 1.6 equiv of CuCl2 was used, yellow-green solid was obtained
in yield of 76.9%. M.p. 237–2388C; 1H NMR (300 MHz, CD2Cl2): d=
8.00 (d, J=8.1 Hz, 1H), 7.81 (dt, J=7.8, 1.8 Hz, 1H), 7.77 (d, J=7.8 Hz,
1H), 7.73 (d, J=8.7 Hz, 1H), 7.51 (ddd, J=8.4, 7.2, 1.2 Hz, 1H), 7.40–
7.22 (m, 3H), 7.25 (d, J=8.7 Hz, 1H), 7.16 (dt, J=7.8, 1.3 Hz, 1H), 7.08
(ddd, J=11.3, 8.1, 1.2 Hz, 1H), 7.04–6.99 (m, 2H), 6.98 (d, J=3.7 Hz,
1H), 6.91 (d, J=3.7 Hz, 1H), 6.49 ppm (dd, J=10.0, 4.4 Hz, 1H);
13C NMR (75 MHz, CDCl3): d=159.0 (1J=248.2 Hz), 149.7, 146.7, 137.8,
136.0, 135.8, 130.6 (2J=10.4 Hz), 130.0, 129.8 (3J=8.5 Hz), 129.6, 129.5,
2684
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Chem. Eur. J. 2007, 13, 2671 –2685

Photochromism
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Published online: December 22, 2006
Chem. Eur. J. 2007, 13, 2671 –2685
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2685