Crystal and solution structures of photochromic spirobenzothiopyran. First full characterization of the meta-stable colored species

Article abstract of DOI:10.1021/jo011011t

Full elucidation for stable, colorless, and meta-stable colored structures of a new spirobenzothiopyran has been achieved both in the solid state and in a solution. 1′,3′,3′-Trimethyl-6-nitrospiro[(2H)-1-benzothiopyran-2, 2′-indoline] with an ester group as a substituent at the 8-position of 1-sp shows photochromism. The blue-green colored species resulted from UV irradiation (365 nm) in one minute and spontaneously bleaches within one minute in acetone and methanol at 27 °C. UV exposure (365 nm) of 1-sp in methanol for 3 h at room temperature results in the growth of deep blue needlelike single crystals of the open form of spirobenzothiopyran, photomerocyanine 1-pmc, whose structures in the solid state and in solution were obtained unambiguously. The X-ray structural analysis of 1-pmc revealed the molecular structure of the zwitterionic photomerocyanine with s-trans,s-trans conformation. 1-pmc is soluble to polar solvents and thermally returns to 1-sp. In the DMSO solution, 1-pmc is found to return slowly to 1-sp (1-pmc gave only 18% of 1-sp for 30 min at 22 °C). The detailed NMR studies in DMSO-d₆ including COSY and NOE techniques as well as isotope labeling of the compound showed the structure with s-trans,s-cis conformation in a solution.

Full text of DOI:10.1021/jo011011t

J . Org. Chem. 2002, 67, 533-540
533
Cr ysta l a n d Solu tion Str u ctu r es of P h otoch r om ic
Sp ir oben zoth iop yr a n . F ir st F u ll Ch a r a cter iza tion of
th e Meta -Sta ble Color ed Sp ecies
Masafumi Hirano,*,† Kohtaro Osakada,‡ Hiroyuki Nohira,† and Akira Miyashita†
Department of Applied Chemistry, Faculty of Engineering, Saitama University, 255 Shimo-ohkubo,
Saitama, Saitama 338-8570, J apan, and Chemical Research Laboratory, Tokyo Institute of Technology,
4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8503, J apan
hrc@cc.tuat.ac.jp
Received October 17, 2001
Full elucidation for stable, colorless, and meta-stable colored structures of a new spirobenzothiopyran
has been achieved both in the solid state and in a solution. 1′,3′,3′-Trimethyl-6-nitrospiro[(2H)-1-
benzothiopyran-2,2′-indoline] with an ester group as a substituent at the 8-position of 1-sp shows
photochromism. The blue-green colored species resulted from UV irradiation (365 nm) in one minute
and spontaneously bleaches within one minute in acetone and methanol at 27 °C. UV exposure
(365 nm) of 1-sp in methanol for 3 h at room temperature results in the growth of deep blue
needlelike single crystals of the open form of spirobenzothiopyran, photomerocyanine 1-p m c, whose
structures in the solid state and in solution were obtained unambiguously. The X-ray structural
analysis of 1-p m c revealed the molecular structure of the zwitterionic photomerocyanine with
s-trans,s-trans conformation. 1-p m c is soluble to polar solvents and thermally returns to 1-sp . In
the DMSO solution, 1-p m c is found to return slowly to 1-sp (1-p m c gave only 18% of 1-sp for 30
min at 22 °C). The detailed NMR studies in DMSO-d6 including COSY and NOE techniques as
well as isotope labeling of the compound showed the structure with s-trans,s-cis conformation in a
solution.
In tr od u ction
resolved resonances of UV-vis, Raman, and IR are
powerful methods for characterization of the short-lived
species,2 the structural information obtained from these
spectroscopic methods is still limited. Studies using
negative photochromic spiropyrans3 and stabilization by
hydrogen bonding,4 by the combination with crown ether
or cyclodextrin,5 and by complexation with chromium6 are
also performed to stabilize and characterize the colored
form of spiropyrans. Although association of spiropyran
and the photomerocyanine is suggested by UV-vis spec-
troscopies in nonpolar7 and polar solvents,8 attempts to
isolate the real meta-stable form of spiropyrans by their
UV exposure or placement in an electrical field9,10 led to
Much attention has been paid to photochromic com-
pounds because of potential utility as molecular informa-
tion devices. Spiropyrans are some of the typical organic
photochromic compounds having high extinction coef-
ficients in the near-infrared region and have been widely
studied on the basis of chemical, physical, and material
points of view.1 Their photochromic behavior is normally
based on the UV irradiation promoted opening of the
spiro ring system to produce the colored species and their
photo and/or thermal relaxation to regenerate the spiro-
pyrans (eq 1 is depicted as a least motion illustration).
(2) (a) Aramaki, S.; Atkinson, G. H. J . Am. Chem. Soc. 1992, 114,
438-444. (b) Chibisov, A. K.; Go¨rner, H. J . Phys. Chem. A. 1997, 101,
4305-4312. (c) Aubard, J .; Maurel, F.; Buntinx, G.; Guglielmetti, R.;
Levi, G. Mol. Cryst. Liq. Cryst. 2000, 345, 203-208.
(3) For examples, see: (a) Hirano, M.; Miyashita, A.; Shitara, H.;
Nohira, H. Chem. Lett. 1991, 1873-1876. (b) Nakano, S.; Miyashita,
A.; Nohira, H. Chem. Lett. 1993, 13-16. (c) Raic, S.; Vorkapic-Furac,
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Ikeda, Y.; Mihara, D.; Kurita, S.; Sawada, A.; Yokoyama, Y. Mol. Cryst.
Liq. Cryst. 2000, 345, 515-520.
The elucidation of their real meta-stable structures is
one of the current topics in this field. Although time-
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Chem. Commun. 1998, 2685-2686.
* To whom correspondence should be addressed. Present address:
Department of Applied Chemistry, Faculty of Technology, Tokyo
University of Agriculture and Technology, 2-24-16 Nakacho, Koganei,
Tokyo 184-8588, J apan. Fax: +81 423 877 500.
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8977-8979. (b) Zhou, J .; Sui, Q.; Huang, B. J . Photochem. Photobiol.
A: Chem. 1998, 117, 129-136.
(6) Miyashita, A.; Iwamoto, A.; Kuwayama, T.; Shitara, H.; Aoki,
Y.; Hirano, M.; Nohira, H. Chem. Lett. 1997, 965-966.
† Saitama University.
‡ Tokyo Institute of Technology.
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Techniques of Chemistry; Wiley-Interscience: New York, 1971; Vol.
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Systems-; Du¨rr, H., Bouas-Laurent, H., Eds.; Elsevier: Amsterdam,
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10.1021/jo011011t CCC: $22.00 © 2002 American Chemical Society
Published on Web 12/27/2001

534 J . Org. Chem., Vol. 67, No. 2, 2002
Hirano et al.
Sch em e 1a
a
Reagents and conditions for 1-sp : (a) ClCH2OMe/AlCl3, room temperature for 1 h and then reflux for 2.5 h, 72%; (b) 1.5 equiv of
silver methacrylate, toluene, reflux for 2 h, 96%; (c) 1.5 equiv of ClCSNMe2, 2 equiv of DABCO, DMF, room temperature for 2 h; 90%; (d)
toluene, reflux for 2 h, 55%; (e) MeOH, 0.7 M NaOH, 20 °C, 10 min, 81%; (f) 1 equiv MeI, CHCl3, 80 °C, 21 h, 79%; (g) 1.0 M KOH, room
temperature for 1 h, 55%; (h) 1 equiv of 7 to 6, 2-butanone, 70 °C for 20 h in the dark, 41%.
deposition of the colored form of spiropyrans as an
amorphous powder or quasi-crystals. Detailed structural
information of these deposits as well as other meta-stable
colored forms of spiropyrans has been quite limited.
Crystallogaphic studies of photomerocyanine (colored
form of spiropyran) of negative photochromic spiropyr-
ans11 as well as model compounds of nonphotochromic
photomerocyanine12 have provided useful information
concerning the meta-stable molecular structure of the
normal photochromic spiropyrans. However, full charac-
terization dealing with the meta-stable structure of
normal photochromic spiropyrans both in a solid and in
solution has not yet been carried out. The present study
shows the first full structural analysis of meta-stable
photomerocyanine formed by UV irradiation, indicating
significant differences between the solid and solution
structures.
Resu lts a n d Discu ssion
Syn th esis a n d Molecu la r Str u ctu r e of Sp ir oben -
zoth iop yr a n . The photochromic spirobenzothiopyran,
8-methacryloxymethyl-1′,3′,3′-trimethyl-6-nitrospiro[(2H)-
1-benzothiopyran-2,2′-indoline] (1-sp ), was prepared by
condensation between 3-methacryloxymethyl-5-nitrothio-
salicylaldehyde (6) and 1,3,3-trimethyl-2-methylenein-
doline (7) in 41% yield as outlined in the Scheme 1.13
Spirobenzothiopyran 1-sp was fully characterized by
NMR, IR, and MS spectra, elemental analysis, and X-ray
structural analysis.
Single crystals of 1-sp suitable for X-ray analysis were
obtained as yellow cubes by recrystallization from a
mixture of benzene and hexane (1:9).
A single crystal contains two crystallographically
independent molecules, which have structures that are
basically similar to each other. An ORTEP drawing of
one of them is shown in Figure 1. Selected bond distances
and angles for 1-sp are listed in Table 1. The most
significant feature in the X-ray structure is the bond
distance S(1)-C(8) [1.91(1) Å] being significantly longer
than the sum of their covalent radii (1.81 Å).14 To
compensate for this feature, the bond S(1)-C(16) [1.74-
(1) Å] is shorter than a typical one.
P h otoch r om ic P r op er ty. Upon exposure of 1-sp to
UV light in polar solvents such as methanol and acetone,
the light yellow solution turned to blue-green. The color
was spontaneously bleached at room temperature when
the irradiation turned off. The thermal bleaching obeys
first-order kinetics, whose rate constants at 27.0 °C as
well as the absorption maximum (λmax) of the colored form
are listed in Table 2.
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2729. (b) Yagi, S.; Maeda, K.; Nakazumi, H. J . Mater. Chem. 1999, 9,
2991-2997. (c) Aldoshin, S. In Organic Photochromic and Thermo-
chromic Compounds; Crano, J . C., Guglielmetti, R. J ., Eds.; Kluwer
Academic/Plenum: New York, 1999; Vol 2, pp 297-355.
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B38, 1980-1984. (b) Lareginie, P.; Lokshin, V.; Samat, A.; Gugliel-
metti, R.; Pepe, G. J . Chem. Soc., Perkin Trans. 2 1995, 107-111. (c)
Raic, S.; Vorkapic-Furac, J .; Hergold-Brundic, A.; Nagel, A.; Mintas,
M.; Mannschreck, A. Croatica Chem. Acta 1996, 69, 987-996.
(13) Hirano, M.; Miyashita, A.; Nohira, H. Chem. Lett. 1991, 209-
212.
(14) Emsley, J . In The Elements, 2nd ed.; Oxford Chemistry Guides;
Clarendon: London, 1990.

Structures of Photochromic Spirobenzothiopyran
J . Org. Chem., Vol. 67, No. 2, 2002 535
F igu r e 2. Molecular structure of photomerocyanine 1-p m c.
All hydrogen atoms are omitted for clarity. Ellipsoids represent
50% probability.
Ta ble 3. Selected Bon d Dista n ces a n d An gles for
Sp ir oben zoth iop yr a n 1-p m c
F igu r e 1. Molecular structure of one of two crystallographi-
cally independent molecules of spirobenzothiopyran 1-sp .
Another molecule has basically the same structure. All hy-
drogen atoms are omitted for clarity. Ellipsoids represent 50%
probability.
Bond Distances (Å)
S(1)-C(16)
O(3)-N(7)
1.701(4)
1.221(4)
1.480(5)
1.450(5)
1.536(5)
1.439(5)
1.446(6)
1.409(6)
1.422(5)
1.545(6)
1.384(7)
1.42(2)
O(2)-N(7)
1.226(5)
1.316(6)
1.414(4)
1.412(5)
1.352(6)
1.395(5)
1.369(5)
1.362(6)
1.532(7)
1.505(5)
1.375(6)
1.400(3)
1.388(8)
1.389(4)
N(6)-C(8)
N(6)-C(25)
N(7)-C(13)
C(8)-C(22)
C(10)-C(11)
C(11)-C(16)
C(13)-C(14)
C(15)-C(16)
C(22)-C(24)
C(26)-C(27)
C(26)-C(31)
C(27)-C(28)
C(29)-C(30)
N(6)-C(26)
C(8)-C(9)
C(9)-C(10)
C(11)-C(12)
C(12)-C(13)
C(14)-C(15)
C(22)-C(23)
C(22)-C(31)
C(26)-C(31)
C(27)-C(28)
C(28)-C(29)
C(30)-C(31)
Ta ble 1. Selected Bon d Dista n ces a n d An gles for
Sp ir oben zoth iop yr a n 1-sp
Bond Distances (Å)
S(1)-C(8)
1.91(1)
1.20(2)
1.42(2)
1.40(2)
1.51(2)
1.27(2)
1.39(2)
1.40(2)
1.35(2)
1.56(2)
1.49(2)
1.42(2)
1.37(3)
1.35(2)
S(1)-C(16)
1.74(1)
1.28(2)
1.50(2)
1.43(2)
1.58(2)
1.52(2)
1.40(2)
1.36(2)
1.43(2)
1.53(2)
1.36(2)
1.40(3)
1.39(2)
O(2)-N(7)
O(3)-N(7)
N(6)-C(8)
N(6)-C(26)
C(8)-C(9)
N(6)-C(25)
N(7)-C(13)
C(8)-C(22)
C(10)-C(11)
C(11)-C(16)
C(13)-C(14)
C(15)-C(16)
C(22)-C(24)
C(26)-C(27)
C(27)-C(28)
C(29)-C(30)
1.400(5)
1.383(7)
C(9)-C(10)
C(11)-C(12)
C(12)-C(13)
C(14)-C(15)
C(22)-C(23)
C(22)-C(31)
C(26)-C(31)
C(28)-C(29)
C(30)-C(31)
Bond Angles (deg)
C(8)-N(6)-C(25)
C(25)-N(6)-C(26)
O(2)-N(7)-C(13)
N(6)-C(8)-C(9)
C(9)-C(8)-C(22)
125.6(3) C(8)-N(6)-C(26)
122.5(4) O(2)-N(7)-O(3)
118.5(5) O(3)-N(7)-C(13)
121.8(4) N(6)-C(8)-C(22)
129.0(4) C(9)-C(10)-C(11)
111.9(3)
122.5(3)
118.9(4)
109.2(3)
127.8(4)
C(10)-C(11)-C(12) 121.9(4) C(11)-C(12)-C(13) 120.2(4)
N(7)-C(13)-C(12) 117.5(3) N(7)-C(13)-C(14) 120.9(4)
C(12)-C(13)-C(14) 121.5(3) C(13)-C(14)-C(15) 119.5(3)
C(14)-C(15)-C(16) 121.5(4) S(1)-C(16)-C(11) 122.0(3)
Bond Angles (deg)
105.4(5)
120.5(10) C(8)-N(6)-C(26)
C(8)-S(1)-C(16)
C(8)-N(6)-C(25)
C(17)-O(4)-C(18) 116.0(11)
110.9(9)
120(1)
S(1)-C(16)-C(15)
C(8)-C(22)-C(23)
N(6)-C(26)-C(27)
120.3(4) C(11)-C(16)-C(15) 117.7(3)
C(25)-N(6)-C(26) 121(1)
O(2)-N(7)-O(3)
O(3)-N(7)-C(13)
S(1)-C(8)-C(9)
N(6)-C(8)-C(9)
C(9)-C(8)-C(22)
111.8(4) C(8)-C(22)-C(24)
127.6(4) N(6)-C(26)-C(31)
112.1(3)
108.6(4)
O(2)-N(7)-C(13)
S(1)-C(8)-N(6)
S(1)-C(8)-C(22)
N(6)-C(8)-C(22)
C(8)-C(9)-C(10)
122(1)
116(1)
105.2(8)
110.1(8)
101.9(9)
128(1)
106.9(8)
112.9(10)
119.0(10)
C(27)-C(26)-C(31) 123.8(3) C(26)-C(27)-C(28) 116.1(5)
C(28)-C(29)-C(30) 121.2(4) C(29)-C(30)-C(31) 118.5(4)
C(9)-C(10)-C(11) 127(1)
has a more polarized structure than the exited state,
suggesting zwitterionic structure of the colored form.16
P h otoin d u ced Cr ysta lliza tion of th e Meta -Sta ble
Color ed F or m a n d th e Molecu la r Str u ctu r e in th e
Solid Sta te. We exposed a methanol solution of 1-sp to
UV light for 3 h at 27 °C in a quartz Schlenk tube under
nitrogen. Deep blue (almost black) needles (abbreviated
as 1-p m c) grew on the surface of the irradiated area.17
Tiny crystalline deposits began to form within 30 min,
and further exposure grew the crystalline deposits.
Single crystals suitable for X-ray crystallography were
selected from the deposits. The molecular structure of
1-p m c was shown in Figure 2, and the selected bond
distances and angles are listed in Table 3.
Two aromatic rings are almost in plane (dihedral angle
) 6.5°), indicating the presence of conjugation along two
aromatic rings in the s-trans,s-trans conformation. The
coloration for 1-p m c is ascribed to such a long π-conjuga-
tion. The bond distance S(1)-C(16) [1.701(4) Å] shows a
typical double-bond character, indicating that the pho-
Ta ble 2. Absor p tion Ma xim a a n d Th er m a l Blea ch in g
Ra tes for th e P h otom er ocya n in e Der ived fr om
Sp ir oben zoth iop yr a n 1-sp in Meth a n ol a n d Aceton e
Solu tion a t 27.0 ( 1.0 °C
λ
max/nm
k/s-1
methanol
acetone
588
673
0.06
0.1
The colored species in acetone has an absorption
maximum around 670 nm, which extends to about 900
nm. This is one of the longest absorption bands of the
organic photochromic compounds and is susceptible to
the light generated by a semiconductive laser.15 The
absorption maximum of 1-p m c in acetone shifted to a
wavelength longer by 85 nm than those in more polar
methanol. This solvatochromic feature of 1-p m c can be
accounted for by the fact that the ground state of 1-p m c
(15) (a) Arakawa, S.; Kondo, H.; Seto, J . Chem. Lett. 1985, 1805-
1808. (b) Tamura, S.; Asai, N.; Seto, J . Bull. Chem. Soc. J pn. 1989,
62, 358-361. (c) Miyashita, A.; Hirano, M.; Nohira, H. J . Mater. Chem.
1993, 3, 221-222. (d) Ichimura, K. In Organic Photochromic and
Thermochromic Compounds; Crano, J . C., Guglielmetti, R. J ., Eds.;
Kluwer/Plenum: New York, 1999; Vol. 2, pp 9-63.
(16) Flannery, J . B., J r. J . Am. Chem. Soc. 1968, 90, 5660-5671.
(17) Photographs of crystals of 1-p m c and the mixed aggregates of
1-p m c and 1-sp are available (PDF files) in Supporting Information.

536 J . Org. Chem., Vol. 67, No. 2, 2002
Hirano et al.
Ch a r t 1
tomerocyanine in the solid state prefers the thione rather
than the thiolate structure. The O(2)-N(7) [1.226(5) Å]
and O(3)-N(7) [1.221(4) Å] bonds are the same within
the experimental error, suggesting contribution of the aci-
nitro structure. The bond distances N(6)-C(8) [1.316(6)
Å] and C(9)-C(10) [1.352(6) Å] indicate double-bond
character, while C(8)-C(9) [1.412(5) Å] and C(10)-C(11)
[1.439(5) Å] are relatively longer than these bonds,
showing bond alternation. Significant bond alternation
is also found in the thiophenyl moiety. The bond dis-
tances C(11)-C(16) [1.446(6) Å], C(11)-C(12) [1.395(5)
Å], and C(13)-C(14) [1.409(6) Å] are longer than those
in C(12)-C(13) [1.369(5) Å] and C(14)-C(15) [1.362(6)
Å]. On the other hand, no significant bond alternation is
found in the benzo ring of the indolenium moiety. Thus,
the crystal structure of 1-p m c is best regarded as the
extensive zwitterionic form as shown in Chart 1.
Of great interest is the blue crystal 1-p m c being
consistent with pure meta-stable photomerocyanine. This
shows sharp contrast to the reported quasi-crystals
composed of both spiropyrans and photomerocyanines.10
The IR spectra and the absorption bands for 1-p m c
involving those for the colorless form 1-sp for comparison
are shown in Figure 3 and Table 4. The IR spectrum of
1-p m c shows intensive νas(N-O) and νs(N-O) bands at
1579 and 1286 cm-1, respectively. The significant lower
shift of the νs(N-O) band is due to the aci-nitro contribu-
tion in 1-p m c. This feature is consistent with the X-ray
structure. A similar frequency shift of the nitro group is
documented for the aggregated photomerocyanine de-
rived from 1′,3′,3′-trimethyl-6-nitrospiro[(2H)-1-benzopy-
ran-2,2′-indoline].9b An intensive band at 1252 cm-1 is
assignable to the ν(CdS) band because this signal is
characteristic of the photomerocyanine derived from
spirobenzothiopyran. A band at 1607 cm-1 for 1-sp , which
is due to the cis-ν(CdC) band for the benzothiopyran ring,
disappears for 1-p m c, suggesting transformation to the
trans form. The other bands are assigned basically
according to the literature.2c,9b,9c,10f,18,19
The photomerocyanine 1-p m c is highly thermally
stable and is stable for more than one year at room
temperature in the solid state, while it immediately
bleaches within a minute in solution. Indeed, 1-p m c is
thermally stable below its melting point (113 °C, DSC),
and it returns to 1-sp when heated above the melting
point. This significant thermal stability of the meta-stable
state is ascribed to the aggregation. Two possible ways
for dye aggregation are known. One is the J aggregation,
where dye dipoles are arranged in a parallel (head-to-
head) way, and another is the H aggregation, where
dyestuff dipoles are arranged in an antiparallel (head-
to-tail) way to compensate for its dipole moment.20
F igu r e 3. IR absorption spectra for spirobenzothiopyran 1-sp
(a) and photomerocyanine 1-p m c (b) in the region 450-2000
cm-1 in KBr disks.
Ta ble 4. Selected Absor p tion Ba n d s of IR Sp ectr a for
1-sp a n d 1-p m c in KBr Disk s a t Room
Tem p er a tu r e (cm -1
)
1-sp
1-p m c
1725(s)
νCdO
νCdC
1718(s)
1654(w)
1637(w)
1629(w)
νCdO
νCdC
1637(w)
1607(m)
1592(w)
1579(w)
1518(s)
νCdC(cis)
νCdC
νCdC
ν
asN-O
1579(vs)
1534(s)
1480(m)
νasN-O
νCdC
δsCH2
1484(s)
1458(m)
1338(vs)
δsCH2
νCdC
νsN-O
1337(m)
1310(vs)
1286(vs)
1252(s)
1155(s)
1067(s)
746(m)
νCdC
νC-N
νsN-O
νCdS
1303(m)
νC-N
1152(s)
1067(m)
743(m)
νsC-C-O
νsC-C-O
ν
asO-C-C
νasO-C-C
δCH
δCH
Related cyanines and merocyanines are known to be
capable of forming both J and H aggregates.21,22 Pho-
tomerocyanine generated from spiropyrans is also re-
ported to form both J and H aggregates in LB films or
cast films.18,19,23 The crystal packing of 1-p m c shows that
the indolinium and the thione rings of two crystallo-
(18) Miyata, A.; Unuma, Y.; Higashigaki, Y. Bull. Chem. Soc. J pn.
1991, 64, 1719-1725.
(19) Uznanski, P. Synth. Met. 2000, 109, 281-285.
(20) Norland, K.; Ames, A.; Taylor, T. Photogr. Sci. Eng. 1970, 14,
295.
(21) Nakahara, H.; Fukuda, K.; Mo¨bius, D.; Kuhn, H. J . Phy. Chem.
1986, 90, 6144-6148.
(22) West, W.; Pearce, S. J . Phys. Chem. 1965, 69, 1894-1903.

Structures of Photochromic Spirobenzothiopyran
J . Org. Chem., Vol. 67, No. 2, 2002 537
F igu r e 4. Crystal packing of photomerocyanine 1-p m c show-
ing alternate dipole stacks.
graphically identical molecules are alternately layered
over, although significant intermolecular interaction (less
than 3.5 Å) is not found among these atoms (Figure 4).
This feature can be accounted for by compensation of the
dipole moment in the crystal, and is basically regarded
as H aggregation involving a 2-fold axis in a unit cell.
Str u ctu r e of 1-p m c in Solu tion . Detail analyses of
the solution structure of the colored species for normal
photochromic spiropyrans have been quite limited be-
cause of their general tendency to cause rapid thermal
relaxation into the stable colorless form and low molar
ratios of the colored species in the photostationary
state.4,24 When the crystals of 1-p m c were dissolved in
polar solvents such as acetone or methanol, rapid and
drastic coloration to deep blue-green took place without
irradiation. The absorption spectrum of the resulting
colored solution was identical to that of the colored
species obtained from 1-sp in acetone or methanol upon
irradiation. It should be noted that the crystals of 1-p m c
dissolved in acetone or methanol also thermally bleached
spontaneously, and the resulting light yellow solution
gave the exactly identical NMR spectrum of the original
1-sp . The colored species of the spirobenzothiopyran
1-p m c does not undergo noticeable structural change for
30 min in DMSO at room temperature (only 18% of
1-p m c returned to 1-sp for 30 min at 22 °C), which has
enabled full spectroscopic determination of the structure
in solution. Compound 1-p m c dissolved immediately
thereafter in DMSO-d6 afforded almost a pure pho-
F igu r e 5. 1H NMR spectra for spirobenzothiopyran 1-sp (a)
and photomerocyanine 1-p m c (b) in DMSO-d6 at room tem-
perature.
as the N-Me group, which notably shifted to a lower field
than 1-sp (2.93 ppm in DMSO-d6). This significant low-
field shift arises from the cationic charge on the nitrogen
in the zwitterionic structure. Indeed, the resonance is
comparable to the N+-Me group in the cationic analogue
1,2,3,3-tetramethylindolenium iodide (4.20 ppm). This
zwitterionic feature is consistent with the significant
solvent effect of the colored species on the absorption
maximum, where the λmax of 1-p m c in acetone shifted to
a wavelength longer by 85 nm than that in methanol.
Two characteristic doublets at 7.63 (d, J ) 16.0 Hz, 1H)
and 9.51 ppm (d, J ) 16.0 Hz, 1H) are assignable to the
alkenylic protons, and the large coupling constant indi-
cates that they are mutually trans. Therefore, only four
candidates are possible for structures in a solution as
illustrated in Chart 2.
1
tomerocyanine structure.25 Figure 5 shows the H NMR
spectrum of the colored form 1-p m c in DMSO-d6 as well
as that of the colorless form 1-sp for comparison. These
1
resonances were unambiguously assigned by using H-
1H COSY.
The geminal methyl groups at the 3′-position of 1-p m c
appear equivalently as a singlet, while these for 1-sp are
magnetically inequivalent. This feature indicates that the
spiro linkage is cleaved to give a planer structure in the
former structure. A new singlet at 4.10 ppm is assigned
1
To assign the R- and â-proton signals in the H NMR
spectrum, we prepared the isotope-labeled 1-d 1-p m c in
12% yield on the basis of 1-d 1-sp (as outlined in Scheme
2), whose R-alkenylic proton is exclusively deuterated
with 50 atom % D content.
(23) (a) Ando, E.; J . Miyazaki, J .; Morimoto, K.; Nakahara, H.;
Fukuda, K. Thin Solid Films 1985, 133, 21-28. (b) Hibino, J .;
Hayashida, T.; Suzuki, M.; Kishimoto, Y. Mol. Cryst. Liq. Cryst. 1994,
255, 243-252. (c) Kato, K.; Shinbo, K.; Suzuki, M.; Kaneko, F. Thin
Solid Films 1994, 243, 480-483. (d) Hirata, Y.; Inoue, T.; Yokoyama,
H.; Mizutani, F. Mol. Cryst. Liq. Cryst. 1999, 327, 249-252. (e)
Tachibana, H.; Yamanaka, Y.; Skai, H.; Abe, M.; Matsumoto, M. Mol.
Cryst. Liq. Cryst. 2000, 345, 149-154.
1
The H NMR spectrum of 1-d 1-p m c clearly indicates
3
a slightly broad singlet (likely due to the J HD coupling)
at 9.51 ppm, while the intensity of the signal at 7.63 ppm
for 1-p m c was significantly decreased by the deuteration.
Thus, the former is unambiguously assigned to the
â-alkenylic proton and the latter is assigned to the
R-alkenylic one.
(24) Hobbley, J .; Melatesta, V. Phys. Chem. Chem. Phys. 2000, 2,
57-59.
(25) Residual peaks are identical to the colorless form 1-sp .

538 J . Org. Chem., Vol. 67, No. 2, 2002
Hirano et al.
Ch a r t 2
enylic proton appears in a significantly low field at 9.51
ppm, while the R-alkenylic proton shows little deshielding
effect (7.63 ppm). This feature suggests that the â-protons
have intermolecular hydrogen bonding with a solvent
molecule or another 1-p m c in solution. Contrary to the
â-proton, the R-proton is expected to be less protic
because of its position in the conjugation system as
depicted in eq 2. This hydrogen bonding is likely due to
stabilization of the s-trans,s-cis conformer in solution.
Sch em e 2
For m ation of Mixed Aggr egates of 1-sp an d 1-pm c.
When a hexane solution of 1-sp was irradiated by UV
light for 3 h at 27 °C, a light orange crystalline precipitate
grew on the surface of vessel of the irradiated beam spot
in 55% yield.17 This orange precipitate also afforded a
deep green-colored solution without irradiation when it
was dissolved into polar solvents such as acetone or
methanol. The NMR spectrum of the orange deposit
shows a mixture of 1-sp and 1-p m c. On the basis of the
1
integration ratio of the H NMR spectrum in DMSO-d6,
the orange precipitate contains 1-p m c up to 43%. There-
fore, this deposit is most likely due to a composite
between 1-sp and 1-p m c in a 1:1 ratio. Similar compos-
ites are reported by Krongauz and co-workers10a,b as
quasi-crystals between spiropyran and photomerocyanine
in 1:1 and 2:1 ratios. Contrary to the NMR data, the IR
spectrum of this orange precipitate is basically identical
to that of 1-sp . Therefore, the conformation and/or
polarization of 1-p m c in this mixture may be different
from that in the pure crystals of 1-p m c.28 This significant
solvent effect in the formation of the deposits is also likely
due to the concentration of the photogenerated colored
form 1-p m c upon irradiation. Because 1-p m c cannot be
stabilized by solvation in hexane and the concentration
of photogenerated 1-p m c is therefore quite low, the short-
lived zwitterionic 1-p m c would interact with another
colorless species 1-sp , rather than another 1-p m c, by
Coulombic interaction to form such a mixed aggregate.
NOE experiments for 1-p m c were carried out to
determine the molecular conformation in solution. Ir-
radiation of the geminal methyl groups at the 3′-position
led to an exclusive enhancement on the integration of
the â-alkenylic proton by 31% and slight reduction on
the integration of the proton at the 6-position by -9.0%.
This fact indicates that the geminal methyl and â-alk-
enylic protons are close to each other and rules out the
s-cis,s-cis and s-cis,s-trans forms in Chart 2, whose
â-proton is farther than their R-proton from the geminal
methyls. The negative NOE for the 6-proton suggests a
linear alignment among the geminal methyls, the â-alk-
enyl proton, and the proton at the 6-position. While no
observable NOE was detected by irradiations to the N-Me
protons and the 4-proton, irradiation to the 6-proton led
to enhancement on the integration of the â-proton by
9.5%. From these experiments, we can conclude that the
solution structure for 1-p m c has the s-trans,s-cis con-
formation. It is interesting that 1-p m c has the s-trans,s-
cis photomerocyanine structure in a solution, while it has
the s-trans,s-trans photomerocyanine structure in the
crystal. Abe and Irie reported MNDO-PM3 calculations
for the photomerocyanine derived from 1′,3′,3′-trimethyl-
6-nitrospiro[(2H)-1-benzopyran-2,2′-indoline], where they
pointed out that the s-trans,s-trans conformer is the most
stable product, but only the s-trans,s-cis conformer has
been reported by NMR.26,27 Our NMR experiments also
show the s-trans,s-cis conformer in a solution. One of
possible reasons for this arises from the intermolecular
interaction in solution because such calculations do not
take into account such an interaction. Indeed, the â-alk-
Con clu sion
The present study reveals the formation of single
crystals of the pure meta-stable photomerocyanine 1-p m c
in s-trans,s-trans conformation by photoinduced crystal-
lization from a spirobenzothiopyran solution. Such pho-
toinduced crystallization of photomerocyanine shows
sharp contrast to the previously reported deposits com-
posed of a mixture of spiropyran and photomerocyanine.
In the pure crystals of the colored form, 1-p m c has the
zwitterionic structure bearing thione and aci-nitro con-
tribution. The crystal packing clearly shows that the
(26) Abe, Y.; Nakao, R.; Horii, T.; Okada, S.; Irie, M. J . Photochem.
Photobiol. A: Chem. 1996, 95, 209-214.
(27) After publication of ref 26, the s-trans,s-trans photomerocyanine
derivative was observed by 1H NMR spectrum (see ref 24).
(28) Recently, some spiropyrans have been found to show the ring
opening with a heterolytic C-O bond cleavage mechanism in a polar
solvent and with an electrocyclic ring-opening mechanism in nonpolar
solvents: Swansburg, S.; Buncel, E.; Lemieux, R. P. J . Am. Chem. Soc.
2000, 122, 6594-6600.

Structures of Photochromic Spirobenzothiopyran
J . Org. Chem., Vol. 67, No. 2, 2002 539
O), 1660 (s, νCdO), 1600 (s, aromatic), 1520 (s, νasN-O), 1345
(s, νsN-O), 820 (s, aromatic). Mp: 127.0-129.0 °C.
dipole moment of 1-p m c is compensated for by the
intermolecular interaction. Contrary to this fact, 1-p m c
is found to have a rigid s-trans,s-cis conformation in
solution. The NMR spectrum showed significant deshield-
ing of the â-alkenylic proton, suggesting intermolecular
hydrogen bonding. Such a significant difference concern-
ing structures of meta-stable photomerocyanine in the
solid and in solution is now revealed. This work will
provide extensive information on the studies of photo-
chromic spiropyrans.
3-Meth acr yloxylm eth yl-2-O-(N,N-dim eth ylth iocar bam -
oyl)-5-n itr osa licyla ld eh yd e (4). Compound 3 (137.6 mg,
0.519 mmol) reacted with N,N-dimethylthiocarbamoyl chloride
(96.2 mg, 0.779 mmol) in the presence of 1,4-diazabicyclo[2.2.2]-
octane (111.7 mg, 1.05 mmol) in dry DMF (3 mL) at room
temperature for 2 h. The yellow solution turned into a dark
brown suspension during the reaction. The resulting solution
was filtered through a Celite pad, and the light brown solution
was evaporated to dryness. The obtained brown tar was
dissolved into ethyl acetate, washed with saturated aqueous
sodium chloride, and dried over anhydrous magnesium sulfate.
Evaporation of the solution to dryness gave a reddish brown
Exp er im en ta l Section
1
tar of 4 in 90% yield (200 mg, 0.57 mmol). H NMR (60 MHz,
Gen er a l. Synthesis and characterization of spirobenzothi-
opyrans and their precursors were carried out under air unless
otherwise noted. UV exposure to form 1-p m c was performed
under a nitrogen atmosphere. 1H and 13C{1H} NMR spectra
and COSY were recorded on Bruker AM-400 (400.13 MHz for
1H), J EOL FX-90Q (89.55 MHz for 1H), or J EOL PMX-60Si
(60 MHz for 1H) instruments. IR spectra were recorded on a
Perkin-Elmer FT-1600 Fourier transfer spectrometer. UV-
vis absorption spectra were measured by a Shimadzu UV-
265FW instrument. UV irradiation was performed by a Ushio
500D (500 W) high-pressure mercury lamp in conjunction with
HOYA HA-30 and U-350 band-pass filters to give a light
emission at 365 nm. Mass spectra were obtained by a Shi-
madzu QP-1000 spectrometer with the electron impact method.
DSC analyses were carried out by a Seiko Instruments DSC-
20 apparatus.
CDCl3): δ 2.0 (m, CH2dCMe, 3H), 3.5 (s, NMe, 6H), 5.3 (s,
-CH2-, 2H), 5.7 (m, CH2dCMe, 1H), 6.2 (m, CH2dCMe, 1H),
8.6 (d, aromatic, J ) 3 Hz, 1H), 8.7 (d, aromatic, J ) 3 Hz,
1H), 10.0 (s, CHO, 1H).
3-Meth a cr yloxym eth yl-2-S-(N,N-d im eth ylth ioca r ba m -
oyl)-5-n itr osa licyla ld eh yd e (5). Compound 4 (9.86 g, 28.8
mmol) dissolved in dry toluene was refluxed for 2 h. Evapora-
tion of the solution gave a brown tar. Silicagel column
chromatography eluted with ethyl acetate/benzene (1/9) gave
pure 5 as light yellow crystals in 55% yield (5.61 g, 15.9 mmol).
1H NMR (400 MHz, CDCl3): δ 2.00 (s, CH2dCMe, 3H), 3.03
(s, NMe, 3H), 3.22 (s, NMe, 3H), 5.47 (s, -CH2-, 2H), 5.68 (s,
CH2dCMe, 1H), 6.22 (s, CH2dCMe, 1H), 8.55 (d, aromatic, J
) 2.7 Hz, 1H), 8.77 (d, aromatic, J ) 2.7 Hz, 1H), 10.39 (s,
CHO, 1H). Mp: 93-98 °C.
Et2O, hexane, benzene, and toluene were distilled from Na/
benzophenone ketyl as an indicator under nitrogen. Methanol
was distilled over Mg(OMe)2 under nitrogen. N,N-Dimethyl-
formamide (DMF) was distilled from molecular sieves (4A)
under reduced pressure. CDCl3 was dried over molecular sieves
(4A). DMSO-d6 was dried over CaH2 at 120 °C for 4 h and then
distilled under reduced pressure. Anhydrous AlCl3 was sub-
limed under reduced pressure with a coldfinger trap. 5-Nit-
rosalicylaldehyde and 2,3,3-trimethylindolenine were pur-
chased from TCI, and N,N-dimethylthiocarbamoyl chloride was
purchased from Aldrich; each was used as received.
3-Ch lor om eth yl-5-n itr osa licyla ld eh yd e (2). 5-Nitrosali-
cylaldehyde (2.00 g, 12.0 mmol) was dissolved in dry chlorom-
ethyl methyl ether (20 mL), and then freshly sublimed
aluminum trichloride (8.01 g, 60.0 mmol) was added under
nitrogen. The reaction mixture was stirred for an hour at room
temperature and then was refluxed for 2.5 h. After the
reaction, ice cooled water was added into the reaction mixture
and the resulting off-white residue was collected. Recrystal-
lization of the off-white solid from hot hexane (500 mL) gave
colorless needles of 2 in 72% yield (1.86 g, 8.63 mmol). 1H NMR
(60 MHz, CDCl3): δ 4.7 (s, CH2Cl, 2H), 8.5 (s, aromatic, 2H),
10.0 (s, CHO, 1H), 12.1 (s, OH, 1H).
Silver Meth a cr yla te. Methacrylic acid (5.12 g, 60.6 mmol)
was added into ice-cooled ammonium water (27%, 12 mL).
After stirring for 30 min at room temperature, the reaction
mixture was evaporated until the ammonia odor disappeared.
Silver nitrate (11.25 g, 66.2 mmol) in water was added into
the solution and stirred overnight. The white precipitate was
filtered, washed with water repeatedly, and dried under
vacuum to give a white powder of silver methacrylate in 71%
(8.37 g, 43.3 mmol). IR (KBr, cm-1): 3000 (w, νC-H), 2950
(w, νC-H), 1650 (w, νCdC), 1550 (s, νasC-O), 1375 (s, νsC-
O).
3-Met h a cr yloxym et h yl-5-n it r osa licyla ld eh yd e. Com-
pound 2 (0.20 g, 0.93 mmol) was reacted with silver meth-
acrylate (0.29 g, 1.5 mmol) in dry toluene at 120 °C for 2 h
under nitrogen. Hot filtration through a Celite pad followed
by evaporation of the resulting solution gave a yellow solid of
3 in 96% yield (0.25 g, 0.89 mmol). 1H NMR (90 MHz, CDCl3):
δ 2.0 (m, CH2dCMe, 3H), 5.3 (s, -CH2-, 2H), 5.7 (m, CH2d
CMe, 1H), 6.2 (m, CH2dCMe, 1H), 8.5 (s, aromatic, 2H), 10.0
(s, -CHO, 1H), 12.0 (br, OH, 1H). IR (KBr, cm-1): 3050 (w, ν
aromatic C-H), 2950 (w, νC-H), 2850 (w, νC-H), 1705 (s, νCd
3-Meth a cr yloxym eth yl-5-n itr oth iosa licyla ld eh yd e (6).
Compound 5 (486.5 mg, 1.38 mmol) was dissolved into
methanol (50 mL), and 0.7 M NaOH (aqueous) was added
dropwise into the solution. The solution was stirred at 20 °C
for 10 min during which the light yellow solution turned red.
The hydrolysis took place within 10 min, and prolonged
reaction afforded corresponding acetals. HCl (aqueous, 1 M)
was added into the reaction mixture, and then the product
was extracted with Et2O. The extract was washed with
saturated NaCl (aqueous) and dried over anhydrous sodium
sulfate. Evaporation of the solution to dryness gave a light
yellow powder in 81% (34.1 mg, 1.12 mmol). 1H NMR (60 MHz,
CDCl3): δ 2.0 (s, CH2dCMe, 3H), 5.3 (s, -CH2-, 2H), 5.7 (s,
CH2dCMe, 1H), 6.2 (s, CH2dCMe, 1H), 8.2 (br. SH, 1H), 8.4
(d, aromatic, J ) 2 Hz, 1H), 8.5 (d, aromatic, J ) 2 Hz, 1H),
10.0 (s, CHO, 1H).
1,2,3,3-Tetr a m eth ylin d olen iu m Iod id e. 2,3,3-Trimeth-
ylindoleniune (1.889 g, 11.86 mmol), chloroform (15 mL), and
methyl iodide (1.804 g, 12.71 mmol) were added into an ampule
tube. The ampule tube was sealed by a torch and heated at
80 °C for 21 h. The resulting pink powder was filtered and
washed with ice-cooled chloroform and then Et2O repeatedly
to give a white powder of 1,2,3,3-tetramethylindolenium iodide
1
in 75% yield (2.69 g, 8.18 mmol). H NMR (60 MHz, D2O): δ
1.7 (s, 3-Me, 6H), 2.9 (s, 2-Me, 3H), 4.0 (s, NMe, 3H), 7.6 (br,
aromatic 4H).
1,3,3-Tr im eth yl-2-m eth ylen ein d olin e (7). 1,2,3,3-Tet-
ramethylindolenium iodide (901.6 mg, 2.992 mmol) was added
into a solution of potassium hydroxide (1.0 M, 10 mL). The
suspension stirred for an hour at room temperature during
which the suspension turned into a yellow oil. The resulting
oil was extracted with Et2O and washed with saturated NaCl
(aqueous) repeatedly followed by drying over anhydrous
sodium sulfate. Evaporation of the solvent gave a light orange
liquid of 1,3,3-trimethyl-2-methyleneindoline in 55% (286.8
1
mg, 1.655 mmol). H NMR (60 MHz, CDCl3): δ 1.2 (s, 3-Me,
6H), 2.9 (s, NMe, 3H), 3.8 (s, 2-CH2, 2H), 6.3-7.1 (m, aromatic,
4H). The isotope-labeled analogue 1,3,3-trimethyl-2-dideute-
riomethyleneindoline was similarly prepared by using D2O and
1
KOD in 90% yield. On the basis of integration of the H NMR
spectrum, the content of deuterium is found to be 32% for
indoline-d0, 18% for indoline-d1, and 50% for indoline-d2. 1H
NMR (400 MHz, CDCl3): δ 1.34 (s, 3-Me, 3H), 3.03 (s, N-Me,

540 J . Org. Chem., Vol. 67, No. 2, 2002
Hirano et al.
3H), 6.53 (d, 7-CH, J ) 7.8 Hz, 1H), 6.75 (t, 5-CH, J ) 7.4 Hz,
1H), 7.08 (d, 4-CH, J ) 7.2 Hz, 1H), 7.13 (t, 6-CH, J ) 7.8 Hz,
1H).
(400 MHz, DMSO-d6): δ 1.79 (s, 3′-Me, 6H), 1.99 (s, CH2dCMe,
3H), 4.10 (s, NMe, 3H), 5.27 (s, 3-CH2-, 2H), 5.79 (s, CH2d
CMe, 1H), 6.16 (s, CH2dCMe, 1H), 7.58 (m, 4′-CH and 6′-CH,
2H), 7.62 (m, 5′-CH and 7′-CH, 2H), 7.78 (s, 6-CH, 1H), 8.74
(s, 4-CH, 1H), 9.51 (br.s, â-CH, 1H). MS (EI, 20 eV) m/z: 437
(M+).
F or m a tion of Mixed Aggr ega tes of 1-sp a n d 1-p m c
fr om Hexa n e. A hexane solution (34 mL) of 1-sp (201.2 mg,
0.461 mmol) was exposed to UV light (365 nm) at 27 °C under
nitrogen for 3 h in a quartz Schlenk tube. From the surface of
the irradiated beam spot, a light orange crystalline powder
was formed in 55% yield (110.0 mg, 0.250 mmol). IR (KBr,
cm-1): 2962 (w, νC-H), 1725 (vs, νCdO), 1637 (w, νCdC),
1606 (w, CdC), 1518 (s, νasN-O), 1337 (s, νsN-O), 1155 (s,
νasC-O), 1067 (s, νsC-O), 746 (s, δC-H). MS (EI, 20 eV) m/z:
436 (M+).
Cr ysta llogr a p h ic Stu d ies. The crystallographic data were
measured on a Rigaku four-circle diffractometer AFC-5S using
Mo KR (λ ) 0.71069 Å) radiation with a graphite crystal
monochromator. The unit cell dimensions were obtained by a
least-squares fit of 25 centered reflections. Intensity data were
collected using the ω-2θ technique to a maximum 2θ of 45.0 °.
The scan rates were 4.0 deg/min for 1-sp , and 4.0 deg/min (2θ
< 35.0°) and 2.0 deg/min for 1-p m c. Three standard reflections
were monitored in every 200 reflections. No systematic varia-
tions in intensity were found. Intensities were corrected for
Lorentz and polarization effects. All non-hydrogen atoms were
found by using the results of the CRYSTAN direct methods.
Crystallographic Parameters are listed as follows. 1-sp : for-
mula ) C24H24N2O4S, formula weight ) 436.52, crystal system
) monoclinic, space group ) Pc, a ) 12.893(2) Å, b ) 14.117-
(4) Å, c ) 12.222(2) Å, â ) 91.91(1)°, V ) 2223.3(8) Å3, Z ) 4,
µ ) 1.713 cm-1, Dcalcd ) 1.305 g cm-3, Dfound ) 1.31 g cm-3
(C6H14:CCl4), crystal size ) 0.1 × 0.1 × 0.2 mm, unique
reflections ) 2669, used reflections [Fo > 3σ(Fo)] ) 2070, R(Rw)
) 0.068 (0.069). 1-p m c: formula ) C24H24N2O4S, formula
weight ) 436.52, crystal system ) triclinic, space group ) P1h,
a ) 9.762(7) Å, b ) 13.495(8) Å, c ) 9.689(5) Å, R ) 91.31(5)°,
â ) 91.91(1)°, γ ) 99.21(6)°, V ) 1106(1) Å3, Z ) 2, µ ) 1.704
cm-1, Dcalcd ) 1.31 g cm-3, crystal size ) 0.75 × 0.21 × 0.10
mm, unique reflections ) 2370, used reflections [Fo > 3σ(Fo)]
) 1846, R(Rw) ) 0.071 (0.073).
8-Meth a cr yloxylm eth yl-1′,3′,3′-tr im eth yl-6-n itr osp ir o-
[(2H)-1-ben zoth iop yr a n -2,2′-in d olin e] (1-sp ). 1,3,3-Trim-
ethyl-2-methyleneindoline (355.7 mg, 2.06 mmol) in 2-bu-
tanone (3 mL) was added into a 2-butanone solution (10 mL)
of 3-methacryloxymethyl-5-nitrothiosalicylaldehyde (610.0 mg,
2.17 mmol). The reaction mixture was heated at 70 °C for 20
h in the dark. After evaporation of solvent, the resulting red
wax was purified by silicagel column chromatography in the
dark, eluting with a mixture of benzene/hexane (1/1). Recrys-
tallization of the resulting yellow solid from a mixture of
benzene/hexane (1/1) gave yellow cubes in 41% yield (374 mg,
0.858 mmol). 1H NMR (400 MHz, CDCl3): δ 1.24 (s, 3′-Me,
3H), 1.39 (s, 3′-Me, 3H), 1.96 (s, CH2dCMe, 3H), 2.68 (s, NMe,
3H), 5.17 (d, 8-CH2-, J ) 14 Hz, 1H), 5.24 (d, 8-CH2-, J ) 14
Hz, 1H), 5.61 (s, CH2dCMe, 1H), 6.05 (d, 3-CH, J ) 11.0 Hz,
1H), 6.17 (s, CH2dCMe, 1H), 6.51 (d, 7′-CH, J ) 7.6 Hz, 1H),
6.67 (t, 5′-CH, J ) 7.6 Hz, 1H), 6.97 (d, 4-CH, J ) 11.0 Hz,
1H), 7.07 (d, 4′-CH, J ) 7.6 Hz, 1H), 7.17 (t, 6′-CH, J ) 7.6
Hz, 1H), 8.02 (d, 5-CH, J ) 2.3 Hz, 1H), 8.09 (d, 7-CH, J ) 2.3
Hz, 1H). IR (CCl4, cm-1): 3033 (w, ν aromatic C-H), 2964 (w,
νC-H), 2868 (w, νC-H), 1725 (s, νCdO), 1637 (w, νCdC), 1607
(m, νCdC), 1518 (s, νasN-O), 1484 (s, δsCH2), 1338 (vs, νsN-
O), 1152 (s, νsC-C-O), 1067 (m, νasO-C-C), 743 (m, δCH).
MS (EI, 70 eV) m/z: 436 (M+). Mp (DSC): 111-116 °C. Anal.
Calcd.: C, 66.04; H, 5.54; N, 6.42%. Found: C, 65.91; H, 5.42;
N, 6.29%. The isotope-labeled compound 1-d 1-sp was also
prepared analogously in 22% yield (50 atom % D). 1H NMR
(400 MHz, CDCl3): δ 1.24 (s, 3′-Me, 3H), 1.39 (s, 3′-Me, 3H),
1.96 (s, CH2dCMe, 3H), 2.68 (s, NMe, 3H), 5.17 (d, 8-CH2-, J
) 14 Hz, 1H), 5.24 (d, 8-CH2-, J ) 14 Hz, 1H), 5.61 (s, CH2d
CMe, 1H), 6.17 (s, CH2dCMe, 1H), 6.51 (d, 7′-CH, J ) 7.6 Hz,
1H), 6.67 (t, 5′-CH, J ) 7.6 Hz, 1H), 6.96 (br.s, 4-CH, 1H),
7.07 (d, 4′-CH, J ) 7.6 Hz, 1H), 7.17 (t, 6′-CH, J ) 7.6 Hz,
1H), 8.02 (d, 5-CH, J ) 2.3 Hz, 1H), 8.09 (d, 7-CH, J ) 2.3 Hz,
1H). MS (EI, 70 eV) m/z: 437 (M+).
P h otoin d u ced Cr ysta lliza tion of P h otom er ocya n in e
1-p m c fr om Meth a n ol. A methanol solution (32 mL) of 1-sp
(108.8 mg, 0.25 mmol) was exposed to UV light (365 nm) at
27 °C for 3 h under nitrogen in a Schlenk tube. From the
surface of the irradiated beam spot, deep blue (almost black)
needles were obtained and washed with methanol followed by
Ack n ow led gm en t. The authors thank Drs. M.
Sasaoka and S. Nakano in Otsuka Chemical Co., Ltd.,
and Mr. H. Shitara in Saitama University for discus-
sions. This work was financially supported by Otsuka
Chemical Co., Ltd.
1
drying under vacuum. Yield: 5.4% (5.9 mg, 0.014 mmol). H
NMR (400 MHz, DMSO-d6): δ 1.79 (s, 3′-Me, 6H), 1.99 (s,
CH2dCMe, 3H), 4.10 (s, NMe, 3H), 5.27 (s, 3-CH2-, 2H), 5.79
(s, CH2dCMe, 1H), 6.16 (s, CH2dCMe, 1H), 7.58 (m, 4′-CH
and 6′-CH, 2H), 7.63 (d, R-CH, J ) 16.0 Hz, 1H), 7.62 (m, 5′-
CH and 7′-CH, 2H), 7.78 (s, 6-CH, 1H), 8.74 (s, 4-CH, 1H),
9.51 (d, â-CH, J ) 16.0 Hz, 1H). IR (KBr, cm-1): 3014 (w, ν
aromatic C-H), 2976 (w, νC-H), 2932 (w, νC-H), 1718 (s, νCd
O), 1637 (w, νCdC) 1579 (vs, νasN-O), 1534 (s, νCdC), 1480
(m, δsCH), 1458 (m, νCdC), 1310 (vs, νC-N), 1286 (vs, νsN-
O), 1252 (s, νCdS), 1155 (s, νsC-C-O), 1067 (s, νasO-C-C),
746 (m, δCH). MS (EI, 20 eV) m/z: 436 (M+). Mp (DSC) ) 113
°C (converted to 1-sp ). The isotope-labeled compound 1-d 1-
p m c was also prepared analogously in 12% yield. 1H NMR
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic data for 1-sp and 1-p m c and photographs of the
photomerocyanine cystals 1-p m c from a methanol solution and
the mixed aggregates of 1-p m c and 1-sp from a hexane
solution. This material is available free of charge via the
Internet at http://pubs.acs.org.
J O011011T