Steric effects on [4+4]-photocycloaddition reactions between complementary anthracene derivatives

Article abstract of DOI:10.1016/j.dyepig.2010.05.016

The steric effect of peripheral functional groups on the [4+4]-photocycloaddition between substituted anthracene derivatives was examined. The reactivity of 2,3,6,7-tetraphenylanthracene (TPA) with 2-phenylanthracene (PA), 2,9,10-trimethylanthracene (TMA) and 9,10-dimethyl-2,3-diphenylanthracene (DMDPA) was investigated. In all cases, the photodimers were formed in high yield despite the steric bulk of the peripheral substituents. It was further shown that although PA is capable of forming its homodimer, it selectively reacts with TPA when the latter is excited at 301 nm.

Full text of DOI:10.1016/j.dyepig.2010.05.016

Dyes and Pigments 89 (2011) 313e318
Contents lists available at ScienceDirect
Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Steric effects on [4þ4]-photocycloaddition reactions between
complementary anthracene derivatives
*
David Bailey, Nasim Seifi, Vance E. Williams
Department of Chemistry, Simon Fraser University, 8888 University Dr., Burnaby, British Columbia, Canada V5A 1S6
a r t i c l e i n f o
a b s t r a c t
Article history:
The steric effect of peripheral functional groups on the [4þ4]-photocycloaddition between substituted
anthracene derivatives was examined. The reactivity of 2,3,6,7-tetraphenylanthracene (TPA) with 2-
phenylanthracene (PA), 2,9,10-trimethylanthracene (TMA) and 9,10-dimethyl-2,3-diphenylanthracene
(DMDPA) was investigated. In all cases, the photodimers were formed in high yield despite the steric
bulk of the peripheral substituents. It was further shown that although PA is capable of forming its
homodimer, it selectively reacts with TPA when the latter is excited at 301 nm.
Received 16 April 2010
Received in revised form
26 May 2010
Accepted 31 May 2010
Available online 16 June 2010
Ó 2010 Elsevier Ltd. All rights reserved.
Keywords:
Anthracene
Photodimer
Photoswitch
[4þ4]-photocycloaddition
1. Introduction
pairs of anthracene derivatives, A and B, capable of reacting with
each other to form AB cyclomers to the exclusion of the AA and BB
Photochromism provides
a
versatile method for toggling
homodimers [27,28]. We have recently reported one such pair;
irradiation of 9,10-dimethylanthracene (DMA) with 2,3,6,7-tetra-
phenylanthracene (TPA) afforded the cross-cyclomer, DMAeTPA as
the exclusive product; the homodimers di-TPA and di-DMA were
not observed (Scheme 1). This selectivity was rationalized in terms
of the orthogonal steric demands placed on the two anthracene
derivatives by their respective functional groups. Thus, the methyl
groups on DMA and the phenyl groups on TPA effectively inhibit
the formation of homodimers, but because these groups do not
interact appreciably in DMAeTPA, they do not prevent the forma-
tion of this cross-cyclomer [27].
These observations prompted us to investigate the scope of
selective cross-cyclization reactions, and in particular their toler-
ance with respect to the number and nature of substituents in the
2-, 3-, 6- and 7-positions. To this end, the photoreactivity of TPA
with the three different anthracene derivatives, TMA, PA, and
DMDPA, was examined. Both TMA and DMDPA possess methyl
groups at the 9- and 10-positions, and are therefore not expected to
form their homodimers. What was less clear was whether deriva-
tives with a methyl or phenyl groups in the peripheral positions
would show an appreciable tendency to react with TPA. The last
derivative, 2-phenylanthracene (PA) lacks groups at the 9- and 10-
positions, and is therefore expected to undergo homodimer
formation; whether it could also react with TPA, and whether the
latter process would be competitive with PA homodimerization
were questions that we wished to address.
molecular properties using light, and has been exploited in an
enormous range of applications. Photochromic systems are most
commonly based on unimolecular processes such as the trans-to-cis
isomerisation of azobenzenes or the electrocyclization of diary-
lethene derivatives [1]. Although bimolecular processes such as the
[4þ4]-photocycloaddition of anthracene derivatives were amongst
the first photochromic systems to be discovered, they have received
much less attention than unimolecular switches [2e4]. Nonethe-
less, the last decade has witnessed a resurging interest in the
photodimerization of anthracenes and related molecules, in part
because they have the ability to bring together two molecules in
a reversible fashion [5]. The [4þ4]-photocycloaddition of anthra-
cene has been used in applications that include [6e11] assembling
and crosslinking of polymers, [12e15] modulating binding proper-
ties of receptors, [7,16] attenuating magnetic interactions [17e19]
and patterning micro- and nano-structured materials [20e23].
Arguably one of the most attractive features of bimolecular
reactions is the potential for bringing together two different
molecules in a selective manner. Such selectivity is ubiquitous for
many classes of thermal reactions, but has been largely unexplored
in the context of [4þ4]-photocycloadditions [5,15,24e26]. Hence,
we have been investigating strategies for designing complementary
* Corresponding author. Tel.: þ1 778 782 8059.
E-mail address: vancew@sfu.ca (V.E. Williams).
0143-7208/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2010.05.016

314
D. Bailey et al. / Dyes and Pigments 89 (2011) 313e318
TMA
DMDPA
PA
The syntheses of TMA and DMDPA are shown in Scheme 2. TMA
four new peaks is consistent with the formation of the photo-
cyclomer TPAeTMA (Fig. 1). The peak at 3.97 ppm was assigned to
the protons a and a0 originating from the TPA fragment, and is
similar to the chemical shift observed for the corresponding protons
in DMAeTPA, which appear at 4.08 ppm [27]. Although not formally
chemically equivalent, it is anticipated that a and a0 should exist in
virtually identical chemical environments, and therefore exhibit
coincident chemical shifts. The remaining peaks in the vicinity of
2.1 ppm were assigned to the methyl protons c, d and e. These peaks
are all considerably shifted relative to those in the parent compound
TPA, which appear at 3.08, 3.07 and 2.59 ppm. The observed shifts
for the methyl protons at the 9- and 10-position are similar to those
seen in the case of DMAeTPA, which shift from 3.11 ppm in DMA to
2.19 ppm in the cyclomer. Such as shift is to be expected, since the
carbons adjacent to the methyl groups change from sp2 to sp3
hybridization. The upfield shift observed for the methyl protons e is
likely due to the protons being shielded by the close proximity of
the phenyl rings from TPA.
Based on these assignments and the relative integrations of the
identifiable (i.e. non-aromatic) peaks from both the starting
materials and the product, the yield of TPAeTMA was estimated to
be approximately 68%. In comparison, TPAeDMA was obtained in
65% yield under similar reactions conditions (300 nm, 4 mM TPA,
4 mM DMA, 140 min), suggesting that the steric hindrance between
the peripheral methyl group at the 2-position of TMA and the
phenyl groups of TPA is not sufficient to significantly impede
reaction between these two chromophores. The extent to which
the steric demands of the methyl group impact on the ability of
TMA to undergo photocyclomerization is difficult to ascertain, since
the yield of product will depend on a variety of factors, including
the degree of photo- and thermal-reversion during the experiment
and on the excited state populations of both molecules under the
irradiation conditions. The excited state population of TMA will, for
example, depend on both how much light it absorbs and its excited
state lifetime. We have not at this time carried out experiments to
determine the extent to which these factors play in the efficiency
with which TMA is able to react with TPA. Nonetheless, the present
observations are encouraging, as they indicate that our comple-
mentary chromophore strategy is relatively tolerant towards
functionalization at the 2-position of 9,10-dimethylanthracene
derivatives. It may be possible to exploit this in order to incorporate
these chromophores into functional materials (e.g. polymers,
surfaces or nanoparticles) via linking groups at the 2-position. We
did not observe thermal decomposition of TPAeTMA during the
was prepared from the reaction of 3-methylanthraquinone (1a)
with methyl magnesium iodide to produce 2a. This intermediate
was not isolated; rather, it was treated in situ with a saturated
solution of HCl/SnCl2 to afford TMA in an overall yield of 30%. The
same approach was employed to prepare DMDPA from 2,3-
diphenylanthraquinone (1b); details of this synthesis have previ-
ously been reported from our group [28].
The synthesis of PA was accomplished in three steps from 2-
aminoanthraquinone (3) using the approach shown in Scheme 3.
Diazotization of 3, followed by treatment with potassium iodide
afforded 2-iodoanthraquinone (4), which was then coupled to
phenylboronic acid under standard Suzuki coupling conditions to
yield 2-phenylanthraquinone (5) in 74% yield. Reduction of this
quinone to PA was accomplished using a two-step method in which
the quinone was first treated with lithium aluminium hydride and
aluminium chloride to afford PA as the major product, along with
a small amount of the over-reduced product, 9,10-dihydro-2-phe-
nylanthracene. Rather than attempt to isolate the desired product
from this intractable mixture, the combined products were sub-
jected to palladium on carbon to oxidize the dihydroanthracene
side product to PA.
With the three anthracene derivatives in hand, we undertook to
investigate their photochemical behaviour in the presence and
absence of TPA. Our initial efforts focused on TMA, since this
compound is structurally most similar DMA, which had previously
been shown to react with TPA. No reaction was observed when
a benzene solution containing only TMA was irradiated for 2 h
using a Rayonet photoreactor with 300 nm lamps. This behaviour is
similar to that of DMA, which also fails to undergo dimerization
under these conditions [27,28]. Under similar conditions, anthra-
cene forms its homodimer in 78% yield [27]. Thus, as expected, this
9,10-disubstituted compound shows little or no tendency to
undergo [4þ4]-photocycloaddition with itself.
In contrast, irradiation of a solution containing 4 mM of TMA and
4 mM TPA affords a single photoproduct. This product was exam-
ined by removing the solvent from the reaction mixture in vacuo;
the residue was then redissolved in deuterated chloroform. The 1H
NMR of the photoproduct exhibited several new peaks in the
aromatic region. Due to significant overlap of these peaks with each
other and those of the starting materials, intepretation based on the
aromatic peaks was difficult. However, four additional singlets were
observed at 3.97 ppm, 2.13 ppm, 2.10 ppm and 2.09 ppm with
relative integrations in a ratio of 2:3:3:3. The observation of these
Scheme 1. Selective photocycloaddition of TPA and DMA to form DMAeTPA as the exclusive product. Homodimers di-DMA and di-DMA were not observed.

D. Bailey et al. / Dyes and Pigments 89 (2011) 313e318
315
O
O
HO
X
Y
X
Y
X
a
b
Y
OH
1a X=CH3, Y=H
1b X=Y=Ph
2a X=CH3, Y=H
2b X=Y=Ph
TMA X=CH3, Y=H (30%)
DMDPA X=Y=Ph (23%)
Scheme 2. Reagents and conditions: a) Mg, CH3I, Et2O, reflux; b) SnCl2, HCl(aq), RT.
course of our experiments, suggesting that 2-methyl group does
not appreciably destabilize the photoproduct.
integration for the 9- and 10-protons of PA, it was estimated that this
compound underwent 90% conversion under these conditions.
Several additional, poorly resolved peaks are observed in the
range 4.68e4.67 ppm when a solution of 4 mM PA and 4 mM TPA
were irradiated under the same conditions; in fact, these peaks
appear to represent the major product (w55%), which is proposed
to be the cyclomer TPAePA. The homodimers are also in evidence
(w25%). It therefore appears that cross-cyclomer formation is able
to compete with PA homodimer formation.
As already noted, further characterization of the photoproduct
by mass spectrometry is complicated by the tendency of photo-
dimers to decompose to monomeric fragments. In the case of the
photoproduct formed upon irradiation of TPA and PA, only a peak
associated with Mþ1 for PA was observed. Although our assign-
ment of this photoproduct as TPAePA must therefore be treated
with caution, the failure to observe peaks other than those of the
monomer is consistent with the product being a dimer rather than
another photoproduct such as an endoperoxide.
The ability of TMA and DMDPA to only form their respective cross-
cyclomer products with TPA relies, as already noted, on their inability
to homodimerize under the conditions examined. These consider-
ations at first glance seem to preclude PA from exhibiting similar
exclusivity, since, if excited, this compound does form its dimer.
However, we have recently shown [28] that specificity for the cross-
cyclomer can also be enforced even in cases where one of the
components is capable of forming its homodimer simply by not
exciting that molecule. This is accomplished by selective irradiation of
the component that is unable to form its homodimer. In this manner,
it was demonstrated that the cross-cyclomer of anthracene and TPA
could be formed as the exclusive product when TPA was excited at
wavelengths where anthracene had a negligible absorbance [28].
We therefore decided to investigate whether this approach
could be extended to PA. The UVevisible spectra of TPA and PA are
shown in Fig. 4. An important feature in the comparison of these
spectra is the strong absorbance band for TPA at 301 nm, a region in
which PA has negligible absorbance. When TPA was selectively
excited at this wavelength in the presence of PA, only the peaks
associated with the cross-cyclomer were observed; the homodimer
peaks were not in evidence. Under the conditions used to carry out
selective irradiation, the product identified as TPAePA was formed
in an estimated 8% yield. The lower yield in this case may be
ascribed to the much lower irradiation levels in this experiment,
which used a fluorimeter as the light source, versus experiments
carried out in a Rayonet.
Similar results are obtained when we examined DMDPA. As noted
elsewhere [28], no photoproduct is observed when this compound is
irradiated by itself in solution. However, exposing a benzene solution
containing 4 mM DMDPA and 4 mM TPA to 350 nm light for 100 min
led to the formation of a single photoproduct with diagnostic peaks in
the 1H NMR at 4.12 ppm and 2.23 ppm, which were assigned as the
protons a and b of TPAeDMDPA (Fig. 2). The chemical shifts of these
peaks are in excellent agreement with 4.08 and 2.19 ppm peaks of
TPAeDMA (vide supra). Based on the relative integration of these
peaks and those of the starting compounds, the yield of this product
was estimated as 64%. Remarkably, then, it appears that even two
relatively large phenyl groups at the 2- and 3-positions of a 9,10-
dimethylanthracene chromophore will still permit these compounds
to readily undergo photodimer formation.
Attempts to characterize this photoproduct by CI mass spec-
trometry yielded only two peaks at m/z ¼ 359 and 483, which
correspond to the Mþ1 peaks for DMDPA and TPA, respectively.
This result is not entirely unexpected, as anthracene photodimers
commonly fragment to their monomers in mass spectrometry
experiments [2]. Thus, while these experiments cannot unambig-
uously confirm the identity of the photoproduct as DMDPAeTPA,
the absence of peaks for other possible photoproducts, such as
endoperoxides, does support the proposed structure.
The UVevisible absorption spectrum of this photoproduct
exhibits a new band centred at 240 nm (Fig. 3b); the sample also
exhibits peaks for residual monomers TPA and DMDPA (Fig. 3a),
which absorb at longer wavelengths. The shorter wavelength of
absorption for the photoproduct is consistent with the decreased
conjugation of the proposed dimer.
We next turned our attention to the reactivity of 2-phenyl-
anthracene (PA). Unlike the other derivatives discussed so far, this
compound lacks functional groups at the 9- and 10-positions, and
therefore is likely to undergo photodimerization on its own. Indeed,
the closely related 2,3-diphenylanthracene readily forms its photo-
dimer [28]. This conjecture was borne out by the observation that
irradiation of an 8 mM solution of PA in a Rayonet for 90 min (350 nm
lamps) led to the formation of a number of photoproducts charac-
terized by multiple 1H NMR peaks in the range 4.64e4.21 ppm,
consistent with the protons at the sp3-hybridized carbons of the
photodimers. In this case, multiple photoproducts are observed
because of the possibility for a variety of regioisomers being formed.
Using the cumulative integration of the peaks in this region and the
O
O
O
NH2
I
Ph
a, b
c
d, e
PA
O
O
O
17%
74%
37%
4
5
3
Scheme 3. Reagents and conditions: a) NaNO2, HCl, H2O, 5 ꢀC; b) KI, H2O, RT; c) phenylboronic acid, Na2CO3, H2O, 1,2-dimethoxyethane, cat. PdCl2(PPh3)2; d) LiAlH3, AlCl3, THF; e)
Pd/C, xylenes.

316
D. Bailey et al. / Dyes and Pigments 89 (2011) 313e318
a
a'
Ph
Ph
Ph
Ph
d
e
c
TPA-TMA
Fig. 1. Proposed structure of photoproduct formed from irradiation of a solution of TPA
and TMA.
2. Conclusion
Our results indicate that although the bulky phenyl substituents
on TPA inhibit its ability to homodimerize, they do not preclude its
reaction with other anthracene derivatives bearing groups in the 2-
and 3-positions. This suggests that a broader range of molecules
can act as complementary pairs in [4 þ 4]-photocycloaddtion
reactions. Most importantly, 9,10-dimethylanthracene derivatives,
which show almost no tendency to homodimerize, can be func-
tionalized at the 2-position without appreciably diminishing their
ability to react with TPA-like derivatives. This opens the door to
creating molecules that are complementary and functional, in
which DMA derivatives are attached via the 2-position to receptors,
catalysts, nanoparticles or polymers. We are actively pursuing these
possibilities.
Fig. 3. UVevisible absorption spectra of (a) TPA (solid) and DMDPA (dashed) and (b)
photoproduct TPAeDMDPA in acetonitrile. Note that the 1H-NMR of the photoproduct
indicates the presence of TPA and DMDPA in the sample used for spectrum b.
aluminum trichloride, lithium aluminum hydride, hexanes and
toluene were purchased from Anachemia. Palladium on carbon (10%
Pd/C) was purchased from Aldrich Chemical Company. Xylenes, THF
and anhydrous MgSO4 purchased from Caledon Laboratories Ltd.
230e400 mesh ASTM silica gel was purchased from EMD Chemicals
Inc. Chemical ionization mass spectrometry experiments were
carried out on a Varian 4000 GC/MS/MS mass spectrometer.
3. Experimental
3.1. Materials and methods
1H NMR spectra were obtained using a Bruker AMX-400
400 MHz spectrometer. Melting Points were determined either on
a Fisher Johns Melting Point Apparatus and are uncorrected.
UVevisible spectrometry was performed on a Cary 100 UVeVis
spectrophotometer. Selective irradiation experiments on TPA/PA
were carried out on a PTI C60 Photon Counting Spectrofluorimeter.
Compound 1a and 3 were obtained from Aldrich Chemical Co.
and used without further purification. Anthraquinone 1b was
prepared according to previously reported methods [29]. Benzene,
Non-selective irradiation experiments were performed under
a nitrogen atmosphere in glass Schlenk tubes. These experiments
were carried out in a Rayonet fitted with ten 300 or 350 nm lamps, as
specified. In a typical experiment, a 2.5 ml benzene solution con-
taining 4 mM of each chromophore was subjected to three freeze-
epumpethaw cycles in order to ensure the exclusion of oxygen from
the reaction mixtures. After irradiation for 2 h, the solvent was
removed in vacuo and the ratio of the products was determined by
a
a
Ph
Ph
Ph
Ph
b
Ph
Ph
b
TPA-DMDPA
Fig. 2. Proposed structure of the photoproduct obtained from irradiating TPA and
DMDPA.
Fig. 4. UVevisible absorption spectra of TPA and PA in acetonitrile.

D. Bailey et al. / Dyes and Pigments 89 (2011) 313e318
317
1H NMR. Selective irradiation experiments were carried out in
deoxygenated CDCl3 solutions in quartz NMR tubes and using
a spectroflourimeter as the light source (slit width ¼ 5 nm) using
a 1 ml solution containing 10 mM of TPA and 10 mM PA.
diethyl ether (3 ꢂ 75 ml). After drying the ethereal layer with
magnesium sulfate, the solution was concentrated in vacuo. This
crude product was then directly applied to a silica gel column and
eluted with a mixture of hexanes and toluene (9:1) 90 mg (41 mmol,
30%) of the desired product was recovered as a yellow solid.1H NMR:
(ppm) (CDCl3) 8.32e8.30 m (2H), 8.24 d (2H, J ¼ 9.0 Hz), 8.07 s (1H),
7.47e7.50 m (2H), 3.08 s (3H), 3.07 s (3H), 2.59 s (3H); mp: 97 ꢀC, lit.
96 ꢀC [33].
2-Iodoanthraquinone (4) 2-Aminoanthraquinone (5 g,
22.3 mmol) was suspended in a mixture of 15 ml HCl and 15 ml ice.
In a separate container 2.7 g (40 mmol) of NaNO2 was dissolved in
15 ml of H2O. While maintaining the 2-aminoanthraquinone
solution in an ice bath the NaNO2 solution was added slowly over
a 20-min period. This solution was then allowed to stir for another
1 h at 5 ꢀC and then carefully poured into a solution of KI (6.6 g,
40 mmol) in 50 ml of H2O and allowed to stir for a further 30 min.
The crude product was then sublimed under vacuum to yield 1.3 g
(3.9 mmol, 17%) of the pure 2-iodoanthraquinone. 1H NMR: (ppm)
(CDCl3) 8.64 d (1H, J ¼ 1.8 Hz), 8.30 m (2H), 8.15 dd (1H, J ¼ 1.8 Hz,
J ¼ 8.2 Hz), 7.99 d (1H, J ¼ 8.2 Hz), 7.82 dd (2H, J ¼ 3.3 Hz, J ¼ 5.8 Hz);
mp: 173e175 ꢀC, lit. 175e176 ꢀC [30].
TPAeTMA 1H NMR (ppm) (CDCl3) 7.20e6.85 m (45H), 3.97 s
(2H), 2.13 s(3H), 2.10 s (3H), 2.09 s (3H)
TPAeDMDPA 1H NMR (ppm) (CDCl3) 7.17e6.93 m (40H), 4.12 s
(2H), 2.23 s (6H).
TPAePA 1H NMR (ppm) (CDCl3) 7.18e6.81 m (54H), 4.682, 4.677,
4.671 (poorly resolved singlet’s, 4H).
Acknowledgments
2-Phenylanthraquinone (5) To
a Schlenk flask, 500 mg
The authors gratefully acknowledge Simon Fraser University and
the Natural Sciences and Engineering Research Council (NSERC) for
funding.
(1.5 mmol) of 2-iodoanthraquinone, 270 mg (2.25 mmol) of phe-
nylboronic acid,1.85 g (15 mmol) of Na2CO3ꢁH2O, 20 mg (0.03 mmol)
of PdCl2(PPh3)2 were added to 10 ml H2O and 4 ml 1,2-dimethoxy-
ethane. This solution was sealed and heated to 80 ꢀC for 48 h. The
solution was then cooled to RT, and poured into Et2O and H2O (30 ml
each). The organic layer was separated and the aqueous layer was
extracted with Et2O (3 ꢂ 30 ml). The combined ethereal extracts
were dried over MgSO4 and concentrated in vacuo resulting in the
desired product in 74% yield (470 mg, 1.65 mmol). This product was
used without further purification. 1H NMR: (ppm) (CDCl3) 8.55 d
(1H, J ¼ 1.9 Hz), 8.39 d (1H, J ¼ 8.1 Hz), 8.35 m (2H), 8.03 dd (1H,
J ¼ 1.9 Hz, J ¼ 8.1 Hz), 7.82 dd (1H, J ¼ 1.2 Hz, J ¼ 2.5 Hz), 7.82 d (1H,
J ¼ 9.1 Hz), 7.74 d (2H, J ¼ 7.1 Hz), 7.53 t (2H, J ¼ 7.3 Hz), 7.47 dt (1H,
J ¼ 4.7 Hz, J ¼ 1.9 Hz); mp: 162e164 ꢀC, lit. 163e164 ꢀC [31].
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2-Phenylanthracene (PA) In an oven-dried 100 mL Schlenk
tube, 2-phenylanthraquinone (300 mg,1.06 mmol) was dissolved in
20 ml dry tetrahydrafuran cooled to ꢃ78 ꢀC in a dry ice/acetone
bath. To this solution 500 mg (3.8 mmol) of lithium aluminum
hydride and 875 mg (18.8 mmol) of aluminum trichloride were
carefully added, this mixture was then allowed to warm to room
temperature and heated at reflux for 24 h under N2. The solution
was then cooled and poured into diethyl ether (50 ml) and carefully
quenched with water (50 ml). After extraction with three further
portions of diethyl ether (50 ml each) the ethereal extracts were
dried with magnesium sulfate, and finally concentrated in vacuo.
This crude product was then dissolved in 50 ml xylenes and
420 mg Pd/C was added to the solution, which was then heated at
reflux for 9 days. The product was then cooled to room temperature
and eluted through a plug of SiO2 with toluene. This resulted in the
170 mg of the desired product, which was recrystallised from
acetone yielding 100 mg (0.39 mmol, 37%) of the desired product as
a yellow solid. 1H NMR: (ppm) (CDCl3) 8.48 s (1H), 8.45 s (1H),
8.21 s (1H), 8.09 d (1H,J ¼ 8.9 Hz), 8.02 dd (1H, J ¼ 1.2 Hz, J ¼ 4.3 Hz),
8.02 d (1H, J ¼ 9.7 Hz), 7.75e7.80 m (3H), 7.51 t (2H, J ¼ 7.6 Hz), 7.47
dd (1H, J ¼ 1.1 Hz, J ¼ 3.4 Hz), 7.47 d (1H, J ¼ 9.7 Hz), 7.40 tt (1H,
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(
¼
7.4 Hz,
J
¼
1.2 Hz); UVeVis: lmax
¼
277 nm
Effects of elastic deformation on phase separation of
a polymer blend
3
¼ 77,000 Mꢃ1cmꢃ1); mp: 206e207 ꢀC, lit. 207e208 ꢀC [32].
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