Synthesis and photoisomerization of dithienylethene-bridged diporphyrins

Article abstract of DOI:10.1021/jo010001p

Dithienylethene-bridged diporphyrins 1-6 were prepared as photochemical switching molecules. Porphyrin and dithienylethene are directly linked in 1, and linked, respectively, through a 1,4-phenylene spacer in 2, through a 4-ethynylphenylene spacer in 3, and through a di-4-phenylethynylene spacer in 4, while meso-ethynylated porphyrin and dithienylethene are directly connected in 5 and linked through a 1,4-phenylene spacer in 6. Compounds 1, 2, and 5 do not undergo any photochemical isomerization, probably due to efficient quenching of the excited dithienylethene by the attached porphyrin moiety via intramolecular energy transfer. Compounds 4 and 6 undergo open-to-closed and closed-to-open photoisomerizations in quantum yields of 4.3 × 10^-2 and 1.8 × 10^-3, and 2.6 × 10^-3 and 7.5 × 10^-4, respectively, by irradiation with 313 and 625 nm light, which are considerably smaller than quantum yields of 0.52 and 3.8 × 10^-3 for reference dithienylethene molecule 7. The fluorescence of 4 was regulated in a reversible manner by the photoisomerization of the dithienylethene moiety. In addition, the absorption properties of the porphyrin in 6 changed in response to the photochromic reaction of the dithienylethene bridge.

Full text of DOI:10.1021/jo010001p

J . Org. Chem. 2001, 66, 3913-3923
3913
Syn th esis a n d P h otoisom er iza tion of Dith ien yleth en e-Br id ged
Dip or p h yr in s
Atsuhiro Osuka,*,† Daisuke Fujikane,† Hideyuki Shinmori,† Seiya Kobatake,‡ and
Masahiro Irie*,‡
Department of Chemistry, Graduate School of Science, Kyoto University, and CREST,
J apan Science Technology Corporation (J ST), Kyoto 606-8502, J apan, and Department of Chemistry and
Biochemistry, Graduate School of Engineering, Kyushu University, and CREST, Hakozaki 6-10,
Higashi-ku, Fukuoka 812-8582, J apan
Received J anuary 2, 2001
Dithienylethene-bridged diporphyrins 1-6 were prepared as photochemical switching molecules.
Porphyrin and dithienylethene are directly linked in 1, and linked, respectively, through a 1,4-
phenylene spacer in 2, through a 4-ethynylphenylene spacer in 3, and through a di-4-phenyl-
ethynylene spacer in 4, while meso-ethynylated porphyrin and dithienylethene are directly connected
in 5 and linked through a 1,4-phenylene spacer in 6. Compounds 1, 2, and 5 do not undergo any
photochemical isomerization, probably due to efficient quenching of the excited dithienylethene by
the attached porphyrin moiety via intramolecular energy transfer. Compounds 4 and 6 undergo
open-to-closed and closed-to-open photoisomerizations in quantum yields of 4.3 × 10-2 and 1.8 ×
10-3, and 2.6 × 10-3 and 7.5 × 10-4, respectively, by irradiation with 313 and 625 nm light, which
are considerably smaller than quantum yields of 0.52 and 3.8 × 10-3 for reference dithienylethene
molecule 7. The fluorescence of 4 was regulated in a reversible manner by the photoisomerization
of the dithienylethene moiety. In addition, the absorption properties of the porphyrin in 6 changed
in response to the photochromic reaction of the dithienylethene bridge.
Ch a r t 1. P h otoisom er iza tion of Dith ien yleth en e
Molecu le a n d Sch em a tic Rep r esen ta tion of Its Use
for P h otoch em ica l Sw itch in g
In tr od u ction
The design of light-driven molecular switches is an
active area of research, since they are crucial for devices
that operate at molecular and supramolecular scales.1-4
A promising approach may be to use photochromic
molecule as a switching component that offers, as a result
of reversible photochemical isomerization, entirely dif-
ferent properties for respective isomeric forms, by which
a key process can be modulated.2-4 Dithienylethene is
an ideal photochromic molecule owing to (1) high ef-
ficiency of “ring-closure” and “ring-opening” photoisomer-
izations for excitations at different wavelength, (2)
sufficient thermal stability of both the “open” and “closed”
forms, (3) very high resistance to photofatigue, and (4)
large differences in ability of the transmission of elec-
tronic interactions (electronic π-conjugation is inter-
rupted in the open form, while electronic π-conjugation
is extended over the closed form).5 In the course of our
program of developing photochemically switchable energy
transfer and electron-transfer molecular systems, we
prepared dithienylethene-bridged diporphyrins 1-6 (Chart
1), and have studied their “closed” and “open” photo-
isomerization efficiencies. Models 1 and 2 bear two 5,15-
diaryl-â-octaalkyl-substituted porphyrins and models 3
and 4 bear two 5,10,15,20-tetraaryl-substituted TPP-type
porphyrins, while models 5 and 6 bear two 5-ethynyl-
10,20-diaryl-substituted porphyrins that are considered
to have a conjugated electronic system well extended to
the ethynyl group at the meso-position and thus have
significantly altered optical properties.6,7 To examine the
effect of the distance between the porphyrin and di-
* To whom correspondence should be addressed. A. Osuka: FAX
81-75-753-3970. M. Irie: irie@cstf.kyushu-u.ac.jp.
† Department of Chemistry, Graduate School of Science, Kyoto
University, and CREST.
‡ Department of Chemisrtry and Biochemistry, Graduate School of
Engineering, Kyushu University, and CREST.
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10.1021/jo010001p CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/03/2001

3914 J . Org. Chem., Vol. 66, No. 11, 2001
Ch a r t 2. Str u ctu r es of Dith ien yleth en e-Br id ged Dip or p h yr in Mod els 1-6
Osuka et al.
thienylethene, we changed the connecting spaces as
follows: (1) directly connected in 1, (2) bridged by a 1,4-
phenylene spacer in 2, (3) bridged by a 4-ethynylphen-
ylene spacer in 3, and (4) bridged by a di-4-phenyl-
ethynylene spacer in 4. meso-Ethynlated porphyrins are
directly connected to dithienylethene in 5 and are bridged
by a 1,4-phenylene spacer in 6. Porphyrin-free dithi-
enylethene 7 was used as the reference molecule. As
described below, the photoisomerization reactivity de-
pends heavily on the distance between the porphyrin and
dithienylethene moieties, and the fluorescence of the
porphyrin is quenched by closed form of the dithienyl-
ethene. The latter observation may be interesting from
a viewpoint of optical switching of emission signal.
enylethene 12. Acid-catalyzed condensation8 of 11 and
benzaldehyde with dipyrrylmethane 139 in a ratio of 1:6:8
followed by oxidation with p-chloranil gave a complicated
mixture of porphyrin products consisting of higher oli-
gomers as revealed by analytical GPC-HPLC. Separa-
tion over size-exclusion chromatography gave diporphy-
rin 1 in 19% yield, along with trimer 14 (11%), tetramer
15 (5%), and pentamer 16 (3%). Molecular weights of
these porphyrin products were determined by MALDI-
TOF MS to be 1923 for 1 (Calcd for C123H154F6N8S2
)
1921), 2982 for 14 (Calcd for C186H230F12N12S4 ) 2988),
4052 for 15 (Calcd for C249H306F18N16S6 ) 4054), and 5102
for 16 (Calcd for C312H382F24N20S8 ) 5121). The dipor-
phyrin 1 was fully characterized also by 500 MHz 1H
NMR but 14-16 were mixtures of syn-anti atropisomers
and their further characterizations were abandoned.
Similar reaction of 12 and benzaldehyde with 13 afforded
porphyrin-dithienylethene dyad 17, and the reaction of
diformyl-substituted dithienylethene 1810 gave diporphy-
rin 2 (Scheme 2).
Resu lts a n d Discu ssion
Syn th esis. Synthetic route to compound 1 is shown
in Scheme 1. Formyl group of 3-bromo-5-formyl-2-meth-
ylthiophene 82b was protected with neopentyl glycol to
afford acetal 9 which was lithiated with n-butyllithium
and then reacted with perfluorocyclopentene to give
dithienylethene 10. Depending upon the hydrolysis con-
ditions, 10 was transformed into diformyl-substituted
dithienylethene 112b or monoformyl-substituted dithi-
Diethynyl-substituted dithienylethene 21 was prepared
from 2,4-dibromo-5-methylthiophene2a via 19 and 20
(Scheme 3). Palladium-catalyzed coupling reaction11 of
4-iodophenyl-substituted TPP-type porphyrin 2211,12 and
(8) Osuka, A.; Nagata, T.; Kabayashi, F.; Maruyama, K. J . Hetero-
cycl. Chem. 1990, 27, 1657.
(9) Nagata, T. Bull. Chem. Soc. J pn. 1991, 64, 3005.
(10) Irie, M. Unpublished results.
(11) Wagner, R. W.; J ohnson, T. E.; Lindsey, J . S. J . Am. Chem.
Soc. 1996, 118, 11166.
(7) (a) Lin, V. S.-Y.; DiMagno, S. G.; Therien, M. J . Science 1994,
264, 1105. (b) Lin, V. S.-Y.; Therien, M. J . Chem. Eur. J . 1995, 1, 645.
(c) Kumble, R.; Palese, S.; Lin, V. S.-Y.; Therien, M. J .; Hochstrasser,
R. M. J . Am. Chem. Soc. 1998, 120, 11489. (d) DiMagno, S. G.; Lin,
S.-Y.; Therien, M. J . J . Org. Chem. 1993, 58, 5983.

Dithienylethene-Bridged Diporphyrins
J . Org. Chem., Vol. 66, No. 11, 2001 3915
Sch em e 1. Syn th esis of 1
Sch em e 2. Syn th esis of 2
21 gave diporphyrin 3. Suzuki coupling13 of boronic acid
232b prepared from 2,5-dibromo-5-methylthiophene with
1-iodo-4-trimethylsilylethynylbenzene 24 gave compound
25, which was reacted with perfluorocyclopentene to give
dithienylethene 7 in 65% yield. The protected dithienyl-
ethene was now converted into 26 by treatment with
NaOH in methanol. Palladium-catalyzed coupling reac-
tion of 26 and 22 furnished diporphyrin 4 in 51% yield
(Scheme 4).
Diporphyrin 5 was prepared by the Sonogashira cou-
pling reaction of meso-bromo porphyrin 277d,14 with 21
in 64% yield, and the similar reaction of 26 and 27 gave
diporphyrin 6 in 64% yield.
Absor p tion a n d F lu or escen ce Sp ectr a of Dip or -
p h yr in Mod es in Op en F or m . The absorption spectra
(12) Osuka, A.; Ikeda, M.; Shiratori, H.; Nishimura, Y.; Yamazaki,
I. J . Chem. Soc., Perkin Trans. 2 1999, 1019.
(13) Miyaura, N.; Suzuki, A. Chem. Rev. 1995, 95, 2457.
(14) Nakano, A.; Osuka, A. Tetrahdron Lett. 1998, 39, 9489.

3916 J . Org. Chem., Vol. 66, No. 11, 2001
Osuka et al.
Sch em e 3. Syn th esis of 3
of 1, 2, and 17 in THF are shown in Figure 1A, where
the absorption spectrum of 5,15-diphenyl-â-octaalkyl-
substituted porphyrin 28 was also included for compari-
son. It was evident that direct attachment of the dithi-
enylethene moiety to the porphyrin had only minor
influence on the absorption bands of the porphyrin
moiety, since the absorption spectra of 1 and 17 were
similar to those of 2 and 28. This may be partly ascribed
to the expected nearly orthogonal conformation of the
dithienylethene moiety with respect to the porphyrin
F igu r e 1. Absorption (A, top) and steady-state fluorescence
spectra (B, bottom) of 1, 2, 17, and 28 in THF. Fluorescence
spectra were taken at the respective peak position of the Soret
bands.
mean plane. Further, the similar absorption spectra of
1 and 17 indicated that the exciton coupling between the
two porphyrins in 1 was not strong enough to alter the
absorption characteristics. This was somewhat in con-
Sch em e 4. Syn th esis of 4

Dithienylethene-Bridged Diporphyrins
J . Org. Chem., Vol. 66, No. 11, 2001 3917
F igu r e 2. Absorption (A, top) and steady-state fluorescence
spectra (B, bottom) of 3, 4, and 29 in THF. Fluorescence
spectra were taken at the respective peak position of the Soret
bands.
F igu r e 3. Absorption (A, top) and steady-state fluorescence
spectra (B, bottom) of 5, 6, and 30 in THF. Fluorescence
spectra were taken at the respective peak position of the Soret
bands.
trast to the frequently observed strong exciton coupling
of covalently linked zinc diporphyrins.15 The absence of
the observable exciton coupling in 1 could be ascribed to
smaller oscillator strength of free-base porphyrin that
was less than the half of the corresponding zinc porphyrin
and to a long distance between the two porphyrin. Figure
1B shows the steady-state fluorescence spectra of 1, 2,
17, and 28, which did not show the significant fluores-
cence quenching of the porphyrin moiety by the attached
diethinylethene.
Figures 2A,B show the absorption and fluorescence
spectra of 3 and 4 along with those of the reference
5,10,15,20-tetrakis(3,5-ditertbutylphenyl)porphyrin 29. It
was also apparent that the optical properties of the
porphyrin moiety in 3 and 4 were scarcely affected upon
the attachment of the ethynylated dithienylethene moi-
eties. Comparison of the absorption and fluorescence
spectra of the meso-phenylethnylated porphyrins 5, 6,
and 5,15-di(3,5-ditertbutylphenyl)-10-phenylethynyl por-
phyrin 30 revealed that the attachment of the dithi-
enylethene moiety had only minor effects except the
observed small red shift in the absorption spectra and
the slightly intensified fluorescence spectra of 5 and 6;
the relative fluorescence quantum yields of 5 and 6 to
the reference 30 are 1.55 and 1.30 (Figures 3A,B).
P h otoisom er iza tion . Reversible photoisomerizations
between the open- and closed-ring forms of dithienyl-
ethenes have been amply demonstrated.4 Essentially in
the same manner, upon irradiation with 330 nm light in
THF open-ring isomer 7 was converted to the closed-ring
isomer 7c (Figure 4A), while irradiation with >550 nm
light gave rise to the closed-to-open cycloreversion to
reform 7 (Figure 4B). The closed-ring isomer 7c was
isolated as a blue solid from the photolyzed mixture. The
photostationary state upon irradiation with 330 nm light
that was attained by several minutes irradiation con-
sisted of a mixture of the open- and closed-ring isomers
in a ratio of 1:3. The quantum yields of the cyclization
and cycloreversion processes were respectively deter-
mined for the irradiation with 313 and 625 nm light to
be 0.52 and 3.8 × 10-3
.
(15) (a) Osuka, A.; Maruyama, K. J . Am. Chem. Soc. 1988, 110, 4454.
(b) Sessler, J . L.; J ohnson, M. R.; Lin, T.-Y. Tetrahedron 1989, 45, 4767.
(c) Matile, S. M.; Berova, N.; Nakanishi, K.; Fleischhauer, J .; Woody,
R. W. J . Am. Chem. Soc. 1996, 118, 5198.
The photoisomerizations of the diporphyrins 1-6 were
also examined in THF. Diporphyrins 1, 2, and 5 with
short separations did not undergo any photoreaction even

3918 J . Org. Chem., Vol. 66, No. 11, 2001
Osuka et al.
F igu r e 5. Photoisomerization of 4 in THF. A, top, open-to-
closed starting from pure open form (s); photostationary state
for excitation at 330 nm (- -) and pure close form (- - -). B,
bottom, close-to-open starting from the photostationary state
(- -); photostationary state for excitation at >550 nm (s).
F igu r e 4. Photoisomerization of 7 in THF. A, top, open-to-
close starting from pure open form (s); photostationary state
for excitation at 330 nm (- -) and pure closed form (- - -). B,
bottom, closed-to-open starting from the photostationary state
(- -); photostationary state for excitation at >550 nm (s).
for extended irradiation with 330 nm light16 but dipor-
phyrins 3, 4, and 6 underwent the reversible photo-
isomerization with different efficiencies.17 Figure 5 shows
the absorption spectral changes of 4 upon irradiation with
UV light (A, open to closed) and with visible light (B,
closed to open). Along with the increase of the irradiation
time, the broad absorption band due to the closed-ring
isomer of a dithienylethene became intensified around
500-700 nm and reached the photostationary state after
several minutes similar to the case of 7. Based on the
spectrum of the closed-ring isomer 4c isolated from the
photoreaction of 4, the photostationary state was revealed
to consist of a 1:3 mixture of 4 and 4c. Irradiation of this
mixture with >550 nm light effected the complete cyclo-
reversion isomerization back to 4. The quantum yields
were determined to be 4.3 × 10-2 and 1.8 × 10-3 for the
open-to-closed and closed-to-open photoisomerizations,
respectively. Here it is interesting to note that the
fluorescence behavior of 4 depended on the degree of the
photoisomerization, since the closed form of the dithi-
enylethene bridge quenched the S1-state fluorescence of
F igu r e 6. Steady-state fluorescence spectra of 4, 4c, and
photostationary mixture of 4 and 4c taken for excitation at
420 nm in THF.
the porphyrin moieties. Comparison of the steady-state
fluorescence spectra of 4 and 4c is shown in Figure 6.
The observed fluorescence quenching in 4c may be
ascribed to the intramolecular energy transfer from the
porphyrin moiety to the closed dithienylethene bridge,
since the energy level of the porphyrin S1-state was
estimated to be 1.91 eV on the basis of the absorption
and fluorescence spectra, while the S1-state of the closed
dithienylethene bridge was estimated to be ca. 1.7-1.8
(16) Similar lack of photoreactivity was reported for porphyrin-
azobenzene system. Hunter, C. A.; Sarson, L. Tetrahedron Lett. 1996,
37, 699.
(17) We could not determine the quantum yields of the photoisomer-
ization of 3 due to unsuccessful isolation of the closed form 3c. But
the open-to-closed photoisomerization quantum yield of 3 has been
estimated slightly better than that of 6.

Dithienylethene-Bridged Diporphyrins
J . Org. Chem., Vol. 66, No. 11, 2001 3919
Sch em e 5. Syn th esis of 5 a n d 6
F igu r e 7. Fluorescence intensity changes of 4 at 650 nm upon
photoirradiation at 330 nm (UV) and >550 nm (vis) taken for
excitation at 430 nm.
eV on the basis of the absorption spectrum. In the view
of the entirely reversible photoisomerization of dithi-
enylethene, these results suggested that the fluorescence
of 4 could be controlled by external light. This was indeed
demonstrated as shown in Figure 7, in which the
fluorescence intensity of 4 was regulated by the photo-
isomerization of the dithienylethene in a reversible
manner.
The open-to-closed photoisomerization of 6 proceeded
upon irradiation with 330 nm light but was rather slow
compared with 7 and 4. Since the isolation of the closed-
ring isomer 6c from the photoreaction of 6 turned out to
be rather tedious, we prepared 6c by palladium-catalyzed
coupling of 27 and 26c (Scheme 6). It is worthy to note
that the closed-ring isomer 26c prepared by the photo-
isomerization of 26 was relatively stable and tolerate
under the present coupling conditions to provide 6c in
74% yield. Figure 8 shows the absorption spectra of 6,
its photostationary state (6 and 6c), and the pure closed
form 6c. The photostationary state was thus determined
to contain only 20% of 6c. The quantum yields for the
open-to-closed and closed-to-open photoisomerizations
were 2.6 × 10-3 and 7.5 × 10-4, respectively, by irradia-
tion with 313 and 625 nm light. Another important
finding was that the absorption bands of the porphyrin
moieties were considerably perturbed in the closed-ring
form, reflecting the substantial electronic interactions
between the porphyrin and dithienylethene bridge. As
shown in Figure 9, the difference spectrum between 6
and 6c indicated the strong signal at the Soret band
region and the negative absorbances at 571 and 660 nm
and the positive absorbances at 620 and 680 nm at the
Sch em e 6. Syn th esis of 6c

3920 J . Org. Chem., Vol. 66, No. 11, 2001
Osuka et al.
In summary, the close attachments of the porphyrin
chromophores to the dithienylethene led to loss of its
photochromic reactivity probably through the intra-
molecular energy transfer quenching but the pertinent
insertion of a spacer between the dithienylethene and
porphyrin ensured the photochromic reactivity that may
trigger the change of the electronic properties of the
porphyrin as seen in 6. This encourages the extension of
this strategy to the control of intramolecular electron
transfer by the reversible dithienylethene photoisomer-
ization that is now actively in progress in our laborato-
ries. In addition, the closed ring form of the dithienyl-
ethene quenches the S1-excited state of the free base
porphyrin and the reversible regulation of the fluores-
cence of the porphyrin is thus possible by the photo-
isomerization of the dithienylethene moiety.
Exp er im en ta l Section
Ma ter ia ls a n d Ap p a r a tu s. All commercially available
materials were used without further purification unless oth-
erwise stated. THF and ether were distilled from sodium-
benzophenone ketyl. DMF was dried over molecular sieve 4A
for 1 day and distilled under reduced pressure. CH2Cl2 was
distilled from P2O5. Pyridine and triethylamine were dried over
KOH for several days and distilled. Toluene was distilled from
CaH2. Solvents used for spectroscopic measurements were all
spectrograde. Preparative separations were usually performed
by flash column chromatography (Merck, Kieselgel 60H, Art.
7736) and gravity column chromatography (Wako, Wakogel
C-200).
1H NMR (500 MHz) spectra were recorded on a J EOL
ALPHA-500 FT-NMR spectrometer, and chemical shifts were
reported in the δ-scale relative to tetramethylsilane. FAB mass
spectra were measured on a J EOL HX-110 spectrometer using
positive-FAB ionization method and 3-nitrobenzyl alcohol
matrix. MALDI-TOF mass spectra were measured on a Shi-
madzu/KRATOS MALDI 4 spectrometer. UV-vis absorption
spectra were recorded on a Shimadzu UV-2400PC UV-vis
spectrophotometer. Steady-state fluorescence spectra were
recorded on a Shimadzu PF-5300PC spectrometer. Steady-
state UV-vis absorption and fluorescence spectra were taken
with 1 × 10-6 M solutions at room temperature. Quantum
yields were determined by comparing the reaction yields of
the dithienylethenes in THF against the yield of furylfulgide
in hexane or toluene.18 As light source, monochromic light was
obtained by passing the light (USHIO 500 W xenon lamp)
through a monochromator (Ritsu MV-10N).
F igu r e 8. Photoisomerization of 6 in THF. A, top, open-to-
closed starting from pure open form (s); photostationary state
for excitation at 330 nm (- -) and pure closed form (- - -). B,
bottom, closed-to-open starting from the photostationary state
(- -); photostationary state for excitation at >550 nm (s).
3-Br om o-2-m eth yl-5-th iop h en eca r boxya ld eh yd e 2,2-
Dim eth ylp r op a n -1,3-d iyl Aceta l (9). 3-Bromo-2-methyl-5-
thiophenecarboxyaldehyde (8) (10.0 g, 48.8 mmol), neopentyl-
glycol (6.09 g, 58.5 mmol), and p-toluenesulfonic acid (1.00 g)
were dissolved in benzene (80 mL). The reaction mixture was
refluxed for 3 h and then cooled and washed with aqueous
sodium bicarbonate (5% w/v, 2 × 150 mL). The combined
benzene layers were then dried (Na2SO4), filtered and evapo-
rated in vacuo to yield acetal 9 as a yellow solid (14.08 g, 99%).
The product was recrystallized from hexane. 9: mp 54.1-57.8
°C; 1H NMR (CDCl3, 500 MHz) δ 0.78 (s, 3H, acetal-Me), 1.25
(s, 3H, acetal-CH3), 2.37 (s, 3H, ArCH3), 3.60 (d, J ) 10.5, 2H,
CH2), 3.72 (d, J ) 11.5, 2H, CH2), 5.51 (s, 1H, CH), and 6.94
(s, 1H, ArH); FTIR (KBr, cm-1) 3080, 2961, 2855, 1091, 1022,
646; MS m/z ) 291 (Calcd 290 for C11H15BrO2S). Anal. Calcd
for C11H15BrO2S‚0.4H2O: C, 44.27; H, 5.35. Found: C, 43.94;
H, 4.87.
F igu r e 9. Light-dark differential spectra of 4, 6, and 7 in
THF.
Q-band region. The negative absorbances roughly cor-
responded to the Q-bands of 6. This was in contrast to
the difference spectrum of 4, which merely displayed the
broad absorption bands of the closed dithienylethene
bridge, being nearly the same as that of 7. In the case of
4, therefore, the influences of the structural change of
the dithienylethene bridge on the absorption spectral
properties of the porphyrins were minor. On the other
hand, the structural change of the dithienylethene bridge
in 6 affected the electronic properties of the porphyrin
moieties through enhanced π-conjugation in the closed
form.
1,2-Bis(5-(5,5-d im eth yl-1,3-d ioxa cycloh ex-2-yl)-2-m eth -
ylth iop h en -3-yl)-p er flu or ocyclop en ten e (10). A solution
of 9 (2.00 g, 6.85 mmol) in dry ether (30 mL) was cooled to
-78 °C under nitrogen atmosphere. n-Butyllithium (1.6 M in
(18) Yokoyama, Y.; Hayata, H.; Ito, H.; Kurita, Y. Bull. Chem. Soc.
J pn. 1990, 63, 1607.

Dithienylethene-Bridged Diporphyrins
J . Org. Chem., Vol. 66, No. 11, 2001 3921
hexane, 4.5 mL, 7.2 mmol) was then added, after 2 h, followed
by perfluorocyclopentene (0.43 mL, 3.44 mmol, added through
cooled syringe). The reaction was stirred for 2 h at -78 °C
after which time the reaction was allowed to warm to ambient
temperature. After an additional 2 h, the reaction was diluted
with diethyl ether, washed with dilute hydrochloric acid (1%
v/v), saturated aqueous sodium bicarbonate, and water, and
extracted with diethyl ether. The combined ether phases were
then dried (MgSO4), filtered, and evaporated in vacuo to yield
a yellow-brown syrup. Chromatography over silica gel (di-
chloromethane/hexane ) 1:1 to 3:1) afforded diarylethene 10
(1.47 g, 72%) as a yellow solid. 10: mp 160.0-162.2 °C; 1H
NMR (CDCl3, 500 MHz) δ 0.79 (s, 6H, acetal-CH3), 1.26 (s,
6H, acetal-CH3), 1.86 (s, 6H, ArCH3), 3.60 (d, J ) 11.0, 4H,
CH2), 3.72 (d, J ) 11.0, 4H, CH2), 5.54 (s, 2H, CH), and 7.08
(s, 2H, ArH); FTIR (KBr, cm-1) 3087, 2963, 2857, 1277, 1086;
MS m/z ) 596 (Calcd 596 for C27H30F6O4S2). Anal. Calcd for
C27H30F6O4S2: C, 54.35; H, 5.07. Found: C, 54.33; H, 5.05.
1,2-Bis(5-for m yl-2-m e t h ylt h iop h e n -3-yl)p e r flu or o-
cyclop en ten e (11). THF (150 mL) and water (40 mL) were
added to a flask containing diacetal (10) (797 mg, 1.34 mmol).
Then, TFA (30 mL) was added to the solution. The resulting
reaction mixture was stirred for 50 min at room temperature,
quenched with saturated aqueous sodium bicarbonate, and
extracted with ether. The combined ether phases were then
washed with aqueous sodium bicarbonate (2% w/v), dried
(Na2SO4), and evaporated in vacuo to yield a yellow syrup.
Chromatography over silica gel (dichloromethane/hexane )
3:1) afforded dialdehyde 11 (406 mg, 71%). 11: mp 179.8-184.5
°C; 1H NMR (CDCl3, 500 MHz) δ 2.01 (s, 6H, ArCH3), 7.71 (s,
2H, ArH), and 9.83 (s, 2H, CHO); FTIR (KBr, cm-1) 3107, 2838,
1666, 1276, 1125; MS m/z ) 425 (Calcd 424 for C17H10F6O2S2).
Anal. Calcd for C17H10F6O2S2: C, 48.11; H, 2.38. Found: C,
47.93; H, 2.43.
filtered, and evaporated. A size exclusion chromatography gave
diporphyrin 1 (41 mg, 19%). 1: 1H NMR (CDCl3, 500 MHz) δ
-2.31 (s, 4H, NH), 0.61 (t, J ) 7.0, 12H, hexyl-6), 0.88 (t, J )
7.0, 12H, hexyl-6), 0.95 (m, 8H, hexyl-5), 1.03 (m, 8H, hexyl-
5), 1.18 (m, 8H, hexyl-4), 1.35 (m, 8H, hexyl-4), 1.45 (m, 8H,
hexyl-3), 1.71 (m, 8H, hexyl-3), 1.79 (m, 8H, hexyl-2), 2.16 (m,
8H, hexyl-2), 2.49 (s, 12H, ArCH3), 2.75 (s, 12H, ArCH3), 2.97
(s, 6H, thiophene-CH3), 3.53 (m, 4H, hexyl-1), 3.69 (m, 4H,
hexyl-1), 3.94 (t, 8H, hexyl-1), 7.76-7.82 (m, 8H, PhH and
thiophene-H), 8.07 (m, 4H, PhH), and 10.16 (s, 4H, meso-H);
MS m/z ) 1923 (Calcd 1921 for C123H154F6N8S2). UV-vis
(THF): λmax(log ꢀ) ) 410 (5.5), 507 (4.7), 541 (4.2), 578 (4.2),
and 630 (4.0). Fluorescence (THF): λmax ) 629, 662, and 696
nm.
P or p h yr in 17. Aldehyde 12 (147 mg, 0.29 mmol), benzalde-
hyde (156 mg, 1.47 mmol), and bis(4-methyl-3-n-hexyl-2-
pyrrolyl)methane (610 mg, 1.78 mmol) were dissolved in 10
mL of acetonitrile. Trichloroacetic acid (20 mg) was added, and
the mixture was stirred for 5 h (dark, under nitrogen, room
temperature). p-Chloranil (720 mg) in 20 mL of tetrahydro-
furan was added, and the mixture was stirred again overnight.
The solvent was evaporated, and the resulting solids were
suspended in chloroform. Concentrated aqueous hydrochloric
acid was added to the solution, and the solution was washed
with aqueous sodium bicarbonate solution and with water,
dried (Na2SO4), and evaporated to yield a black solid. The solid
was dissolved in dichloromethane, and to the solution of the
reaction in dichloromethane was added a saturated solution
of zinc acetate in methanol. The mixture was heated to reflux
for 30 min and then cooled, washed with water, dried (Na2SO4),
filtered, and evaporated to yield a red solid. Chromatography
over silica gel (dichloromethane/hexane) afforded the zinc
complex of porphyrin 17 (161 mg, 42%). A solution of the zinc
complex of porphyrin 17 (23 mg, 17 µmol) in dichloromethane
was washed with aqueous hydrochloric acid (1 M) twice,
washed with saturated aqueous sodium bicarbonate, dried
(Na2SO4), and evaporated to yield the porphyrin 17 (21 mg,
96%) as a red solid. 17: 1H NMR (CDCl3, 500 MHz) δ -2.35
(s, 2H, NH), 0.84 (s, 3H, acetal-CH3), 0.90 (m, 12H, hexyl-6),
1.32 (s, 3H, acetal-CH3), 1.37 (m, 8H, hexyl-5), 1.51 (m, 8H,
hexyl-4), 1.74 (m, 8H, hexyl-3), 2.19 (m, 8H, hexyl-2), 2.32 (s,
3H, thiophene-CH3), 2.47 (s, 8H, ArCH3), 2.52 (s, 3H, thiophene-
CH3), 2.82 (s, 6H, ArCH3), 3.68 (d, J ) 12, 2H, CH2), 3.81 (d,
J ) 12, 2H, CH2), 3.99 (m, 8H, hexyl-1), 5.54 (s, 1H, acetal-
CH), 7.18 (s, thiophene-H), 7.72-7.79 (m, 4H, PhH and
thiophene-H), 8.06 (m, 2H, PhH), and 10.24 (s, 2H, meso-H);
MS m/z ) 1260 (Calcd 1259 for C75H92F6N4O2S2). UV-vis
(THF): λmax (log ꢀ) ) 409 (5.4), 507 (4.3), 540 (3.9), 577 (3.9),
and 630 (3.6). Fluorescence (THF): λmax ) 629 and 696 nm.
Dip or p h yr in 2. Dialdehyde 18 (40 mg, 66 µmol), benz-
aldehyde (47 mg, 443 µmol), and bis(4-methyl-3-n-hexyl-2-
pyrrolyl)methane (13) (176 mg, 514 µmol) were dissolved in
20 mL of acetonitrile. Trichloroacetic acid (27 mg) was added,
and the mixture was stirred for 5 h in the dark under nitrogen,
at room temperature. p-Chloranil (210 mg) in 15 mL of THF
was added, and the mixture was stirred again overnight. The
solvent was evaporated, and the resulting solids were sus-
pended in chloroform. Concentrated aqueous hydrochloric acid
was added to the solution, and the solution was washed with
aqueous sodium bicarbonate solution and with water, dried
(Na2SO4), and evaporated to yield a black solid. To a solution
of the reaction in dichloromethane, a saturated solution of zinc
acetate in methanol was added. The mixture was stirred for 1
h at room temperature, washed with water, dried (Na2SO4),
and evaporated. Chromatography over silica gel (dichloro-
methane/hexane) gave a mixture of zinc porphyrin products.
A size exclusion chromatography gave zinc complex of the
diporphyrin 2, which was demetalated with aqueous hydro-
chloric acid (1 M) to yield the diporphyrin 2 (18 mg, 13% from
dialdehyde). 2: 1H NMR (CDCl3, 500 MHz) δ -2.38 (s, 4H,
NH), 0.82-0.91 (m, 24H, hexyl-6), 1.35 (m, 16H, hexyl-5), 1.45
(m, 16H, hexyl-4), 1.71 (m, 16H, hexyl-3), 2.17 (m, 16H, hexyl-
2), 2.45 (s, 6H, ArCH3), 2.49 (s, 6H, ArCH3), 2.49 (s, 3H,
thiophene-CH3), 2.52 (s, 3H, thiophene-CH3), 2.57 (s, 6H,
ArCH3), 2.58 (s, 6H, ArCH3), 2.61 (s, 3H, thiophene-CH3), 2.65
1-(5-(5,5-Dim et h yl-1,3-d ioxa cycloh ex-2-yl)-2-m et h yl-
t h iop h en -3-yl)-2-(5-for m yl-2-m et h ylt h iop h en -3-yl)p er -
flu or ocyclop en ten e (12). THF (100 mL) and water (25 mL)
were added to a flask containing diacetal 10 (496 mg, 0.825
mmol). Then, TFA (20 mL) was added to the solution. The
reaction mixture was stirred for 2.5 h at room temperature,
quenched with saturated aqueous sodium bicarbonate (200
mL), extracted with ether (100 mL), and washed with aqueous
sodium bicarbonate (2% w/v, 200 mL). The combined ether
phases were then dried (Na2SO4), filtered, and evaporated in
vacuo to yield a yellow syrup. Chromatography over silica gel
(dichloromethane/hexane ) 3:1) afforded diacetal 10 (56 mg,
11%), monoacetal 12 (290 mg, 69%), and dialdehyde 11 (91
mg, 26%). 12: mp 115.5-119.8 °C; 1H NMR (CDCl3, 500 MHz)
δ 0.77 (s, 3H, acetal-CH3), 1.23 (s, 3H, acetal-CH3), 1.83 (s,
3H, ArCH3), 1.98 (s, 3H, ArCH3), 3.60 (d, J ) 8, 2H, CH2),
3.70 (d, J ) 12, 2H, CH2), 5.52 (s, 1H, CH), 7.04 (s, 1H, ArH),
7.71 (s, 1H, ArH), and 9.82 (s, 1H, CHO); FTIR (KBr, cm-1
)
3059, 2956, 2834, 1666, 1274, 1100; MS m/z ) 510 (Calcd 510
for C22H20F6O3S2). Anal. Calcd for C22H20F6O3S2: C, 51.76; H,
3.95. Found: C, 52.02; H, 4.03.
Dip or p h yr in 1. Dialdehyde (11) (47 mg, 0.11 mmol),
benzaldehyde (74 mg, 0.70 mmol), and bis(4-methyl-3-n-hexyl-
2-pyrrolyl)methane (13) (315 mg, 0.92 mmol) were dissolved
in 20 mL of acetonitrile. Trichloroacetic acid (50 mg) was
added, and the mixture was stirred for 5 h (dark, under
nitrogen, room temperature). p-Chloranil (360 mg) in 10 mL
of tetrahydrofuran was added, and the mixture was stirred
again overnight. The solvent was evaporated, and the resulting
solids were suspended in chloroform. Concentrated aqueous
hydrochloric acid was added to the solution, and the solution
was washed with aqueous sodium bicarbonate solution and
with water, dried (Na2SO4), and evaporated to yield a black
solid. To a solution of the reaction in dichloromethane, a
saturated solution of zinc acetate in methanol was added. The
mixture was stirred for 30 min at room temperature, washed
with water, dried (Na2SO4), and evaporated. Chromatography
over silica gel (dichloromethane) gave a mixture of zinc
porphyrins. A solution of the mixture in dichloromethane was
washed with aqueous hydrochloric acid (1 M) twice, washed
with saturated aqueous sodium bicarbonate, dried (Na2SO4),

3922 J . Org. Chem., Vol. 66, No. 11, 2001
Osuka et al.
(s, 3H, thiophene-CH3), 3.98 (m, 16H, hexyl-1), 7.70-7.80 (m,
6H, PhH), 7.84 (d, J ) 8.0, 4H, phenylene), 8.13 (d, J ) 7.5,
2H, phenylene), 8.15 (d, J ) 8.0, 2H, phenylene), 10.20 (s, 2H,
meso-H), and 10.24 (s, 2H, meso-H); MS m/z ) 2102 (Calcd
2101 for C137H166F6N8S2). UV-vis (THF): λmax(log ꢀ) ) 409
(5.7), 506 (4.7), 538 (4.2), 575 (4.3), and 628 (3.8). Fluorescence
(THF): λmax)628 and 695 nm.
3-Br om o-2-m et h yl-5-t r im et h ylsilylet h yn ylt h iop h en e
(19). A degassed solution of 3,5-dibromo-2-methylthiophene
(5.23 g, 20.4 mmol) in 200 mL of Et3N was added Pd(PPh3)4
(961 mg, 0.83 mmol), CuI (314 mg, 1.65 mmol), and trimethyl-
silylacetylene (TMSA) (1.0 mL, 7.1 mmol). The resulting
mixture was stirred at 45 °C for 7 h. The solvent was removed
under reduced pressure and the residue was filtered through
a short plug of silica gel eluting with hexane. The solvent was
evaporated, and the residue was purified by column chroma-
tography (hexane) to yield 1 as a yellow solid (1.17 g, 4.30
mmol, 61% from TMSA). 19: mp 58.5-60.2 °C; 1H NMR
(CDCl3, 500 MHz) δ 0.24 (s, 9H, Si(CH3)3), 2.36 (s, 3H, ArCH3),
and 7.02 (s, 1H, ArH); FTIR (KBr, cm-1) 3103, 2961, 2896,
2150, 849, 646; MS m/z ) 274 (Calcd 274 for C10H13BrSSi).
Anal. Calcd for C10H13BrSSi: C, 43.95; H, 4.80. Found: C,
43.92; H, 4.60.
(4.6), 551 (4.4), 592 (4.1), and 648 (3.8). Fluorescence (THF):
λmax ) 650 and 717 nm.
3-Br om o-2-m eth yl-5-(4-tr im eth ylsilyleth yn ylp h en yl)-
th iop h en e (25). A degassed solution of boronic acid 23 (1.77
g, 8.02 mmol) and iodide 24 (2.43 g, 8.09 mmol) in tetrahy-
drofuran (40 mL) and aqueous sodium carbonate (20% w/v,
25 mL) was added tetrakis(triphenylphosphine)palladium(0)
(347 mg, 0.30 mmol). The reaction was refluxed under a argon
atmosphere for 20 h and then cooled, extracted with chloro-
form, and washed with water. The combined organic phases
were dried (Na2SO4) and evaporated. Chromatography over
silica gel (hexane) and recrystallization from methanol gave
25 as a white solid (2.06 g, 5.90 mmol, 73%). 25: mp 78.8-
1
82.2 °C; H NMR (CDCl3, 500 MHz) δ 0.26 (s, 9H, Si(CH3)3),
2.42 (s, 3H, thiophene-CH3), 7.12 (s, 1H, thiophene-H), and
7.44 (s, 4H, phenylene-H); FTIR (KBr, cm-1) 3027, 2959, 2158,
1505, 838, 633; MS m/z ) 348 (Calcd 348 for C16H17BrSSi).
Anal. Calcd for C16H17BrSSi: C, 55.01; H, 4.90. Found: C,
54.95; H, 4.70.
1,2-Bis(5-(4-t r im et h ylsilylet h yn ylp h en yl)-2-m et h yl-
th iop h en -3-yl)p er flu or ocyclop en ten e (7). A solution of
bromide 25 (1.12 g, 3.21 mmol) in dry ether (30 mL) was cooled
to -78 °C under a nitrogen atmosphere. n-Butyllithium (1.6
M in hexane, 2.1 mL, 3.4 mmol) was then added, after 2 h,
followed by perfluorocyclopentene (0.20 mL, 1.6 mmol, added
through cooled syringe). The reaction mixture was stirred for
1 h at -78 °C, after which time the reaction was allowed to
warm to ambient temperature. After an additional 2 h, the
reaction was diluted with diethyl ether, washed with dilute
hydrochloric acid (1% v/v) and water, and reextracted with
diethyl ether. The combined ether phases were then dried
(Na2SO4), filtered, and evaporated in vacuo to yield a yellow-
brown syrup. Chromatography over silica gel (dichloromethane/
hexane) afforded dithienylethene 7 (745 mg, 65%) as a bluish
white solid. 7: mp 92.5-94.8 °C; 1H NMR (CDCl3, 500 MHz) δ
0.26 (s, 18H, Si(CH3)3), 1.97 (s, 6H, thiophene-CH3), 7.28 (s,
2H, thiophene-H), and 7.46 (s, 8H, phenylene-H); FTIR (KBr,
cm-1) 3032, 2960, 2157, 1508, 1275, 1139, 865; MS m/z ) 712
(Calcd 712 for C37H34F6S2Si2). Anal. Calcd for C37H34F6S2Si2:
C, 62.33; H, 4.81. Found: C, 62.57; H, 4.57.
1,2-Bis(5-(4-tr im eth ylsilyleth yn yl)-2-m eth ylth iop h en -
3-yl)p er flu or ocyclop en ten e (20). A solution of bromide 19
(1.81 g, 6.64 mmol) in dry ether (45 mL) was cooled to -78 °C
under a nitrogen atmosphere. n-Butyllithium (1.5 M in hexane,
4.4 mL, 3.5 mmol) was added, and after 2 h perfluorocyclo-
pentene was added (0.44 mL, 3.2 mmol, added through cooled
syringe). The reaction mixture was stirred for 2 h at -78 °C,
after which time the reaction was allowed to warm to ambient
temperature. After an additional 2 h, the reaction was diluted
with diethyl ether, washed with dilute hydrochloric acid (1%
v/v) and water, and extracted with diethyl ether. The combined
ether phases were then dried (Na2SO4) and evaporated in
vacuo to yield a yellow-brown syrup. Chromatography over
silica gel (dichloromethane/hexane) afforded diarylethene 20
(1.28 g, 69%) as a bluish white solid. 20: mp 99.5-101.8 °C;
1H NMR (CDCl3, 500 MHz) δ 0.25 (s, 18H, Si(CH3)3), 1.88 (s,
6H, ArCH3), and 7.19 (s, 2H, ArH); FTIR (KBr, cm-1) 2962,
2150, 1275, 1136, 846; MS m/z ) 560 (Calcd 560 for
1,2-Bis(5-(4-et h yn ylp h en yl)-2-m et h ylt h iop h en -3-yl)-
p er flu or ocyclop en ten e (26). To a flask containing 7 (307
mg, 0.43 mmol) was added a solution of NaOH (252 mg, 6.3
mmol) in methanol (20 mL), and the mixture was stirred at
room temperature for 3 h. The reaction was diluted with
diethyl ether, washed with water, and reextracted with diethyl
ether. The combined ether phases were then dried (Na2SO4)
and evaporated. Chromatography over silica gel (dichloro-
methane/hexane) afforded 26 (192 mg, 0.34 mmol, 78%) as a
C
25H26F6S2Si2). Anal. Calcd for C25H26F6S2Si2: C, 53.55; H,
4.67. Found: C, 53.59; H, 4.65.
1,2-Bis(5-(4-eth yn yl)-2-m eth ylth iop h en -3-yl)p er flu or o-
cyclop en ten e (21). To a flask containing 20 (600 mg, 1.07
mmol) was added a solution of NaOH (428 mg, 10.7 mmol) in
methanol/THF (60 mL/15 mL), and the resulting mixture was
stirred at room temperature for 30 min. The reaction was
diluted with dichloromethane, washed with water, and ex-
tracted with dichloromethane. The combined dichloromethane
phases were then dried (Na2SO4) and evaporated. Chroma-
tography over silica gel (dichloromethane/hexane) afforded 21
(296 mg, 0.71 mmol, 66%) as a bluish white solid. 21: mp 95.1-
96.5 °C; 1H NMR (CDCl3, 500 MHz) δ 1.91 (s, 6H, ArCH3),
3.35 (s, 2H, CH), and 7.23 (s, 2H, ArH); FTIR (KBr, cm-1) 3305,
2909, 2108, 1274, 1134, 669, 625; MS m/z ) 416 (Calcd 416
for C19H10F6S2). Anal. Calcd for C19H10F6S2Si2: C, 54.80; H,
2.42. Found: C, 54.93; H, 2.53.
1
bluish white solid. 26: mp 164.2-166.5 °C; H NMR (CDCl3,
500 MHz) δ 1.98 (s, 6H, thiophene-CH3), 3.15 (s, 2H, ethynyl-
H), 7.29 (s, 2H, thiophene-H), and 7.49 (s, 8H, phenylene-H);
FTIR (KBr, cm-1) 3305, 3030, 2917, 2107, 1471, 1273, 1104,
648, 612; MS m/z ) 568 (Calcd 568 for C31H18F6S2). Anal. Calcd
for C31H18F6S2: C, 65.48; H, 3.19. Found: C, 65.32; H, 3.40.
Dip or p h yr in 4. A degassed solution of 26 (86 mg, 151 µmol)
and 5-(4-iodophenyl)-10,15,20-tris(3,5-ditertbutylphenyl)por-
phine (22) (402 mg, 373 µmol) in 50 mL of toluene/Et3N (1:4)
were added Pd2(dba)3 (84 mg, 91 µmol) and AsPh3 (233 mg,
761 µmol). The resulting mixture was stirred at 35 °C for 4 h.
The solvent was removed under reduced pressure, and the
residue was filtered through a short plug of silica gel eluting
with dichloromethane. The solvent was evaporated, and the
residue was purified by a size exclusion chromatography and
column chromatography (dichloromethane/hexane) to yield
porphyrin dimer 4 (190 mg, 77 µmol, 51%). 4: 1H NMR (CDCl3,
500 MHz) δ -2.68 (s, 4H, NH), 1.53 (s, 54H, t-Bu), 2.06 (s,
6H, thiophene-CH3), 7.40 (s, 2H, thiophene-H), 7.64 (d, J )
8.0, 4H, phenylene-H), 7.71 (d, J ) 8.0, 4H, phenylene-H), 7.79
(s, 2H, Ph-H), 7.80 (s, 4H, Ph-H), 7.95 (d, J ) 8.0, 4H,
phenylene-H), 8.07 (d, J ) 1.5, 4H, Ph-H), 8.09 (d, J ) 1.5,
8H, Ph-H), 8.25 (d, J ) 7.5, 4H, phenylene-H), 8.86 (d, J )
4.5, 4H, â-H), and 8.90 (s+d, 4H+2H, â-H); MS m/z ) 2466
(Calcd 2466 for C167H170F6N8S2). UV-vis (THF): λmax (log ꢀ)
Dip or p h yr in 3. A degassed solution of 21 (36 mg, 86 µmol)
and 5-(4-iodophenyl)-10,15,20-tris(3,5-ditertbutylphenyl)por-
phine (22) (193 mg, 179 µmol) in 25 mL of toluene/Et3N (1:4)
were added Pd2(dba)3 (14 mg, 15 µmol) and AsPh3 (46 mg, 150
µmol). The resulting solution was stirred at 45 °C for 20 h.
The solvent was removed under reduced pressure, and the
residue was filtered through a short plug of silica gel eluting
with dichloromethane. The solvent was evaporated, and the
residue was purified by column chromatography (dichloro-
methane/hexane) to yield diporphyrin 3 (95 mg, 41 µmol, 48%).
3: 1H NMR (CDCl3, 500 MHz) δ -2.69 (s, 4H, NH), 1.52 (s,
54H, t-Bu), 2.09 (s, 6H, thiophene-CH3), 7.45 (s, 2H, thiophene-
H), 7.79 (s, 3H, Ph-H), 7.92 (d, J ) 8.0, 4H, phenylene-H), 8.07
(d, J ) 2.0, 4H, Ph-H), 8.08 (d, J ) 2.0, 8H, Ph-H), 8.25 (d, J
) 8.0, 4H, phenylene-H), 8.84 (d, J ) 1.5, 4H, â-H), and 8.90
(s+d, J ) 6.5, 8H+4H, â-H); MS m/z ) 2314 (Calcd 2313 for
C
155H162F6N8S2). UV-vis (THF): λmax(log ꢀ) ) 421 (6.0), 516

Dithienylethene-Bridged Diporphyrins
J . Org. Chem., Vol. 66, No. 11, 2001 3923
) 420 (6.1), 515 (4.7), 551 (4.5), 592 (4.1), and 648 (4.1).
Fluorescence (THF): λmax) 650 and 717 nm.
10.14 (s, 2H, meso-H); MS m/z ) 2515 (Calcd 2513 for
C159H186F6N8O8S2). UV-vis (THF): λmax (log ꢀ) ) 437 (5.8),
527.5 (4.5), 571 (4.9), 604 (4.2), and 663 (4.4). Fluorescence
(THF): λmax ) 663 and 735 nm.
Closed F or m of Dip or p h yr in 4c. A solution of 4 in THF
was irradiated with UV light (330 nm) for 5 min. The solvent
was removed under reduced pressure, and the residue was
purified by column chromatography (dichloromethane/hexane)
to isolate porphyrindimer 4c. 4c: 1H NMR (CDCl3, 500 MHz)
δ -2.68 (s, 4H, NH), 1.53 (s, 54H, t-Bu), 2.27 (s, 6H, thiophene-
CH3), 6.79 (s, 2H, thiophene-H), 7.66 (d, J ) 7.5, 4H, phen-
ylene-H), 7.73 (d, J ) 8.0, 4H, phenylene-H), 7.80 (s, 6H, Ph-
H), 7.95 (d, J ) 8.0, 4H, phenylene-H), 8.07 (d, J ) 2.0, 4H,
Ph-H), 8.09 (d, J ) 1.5, 8H, Ph-H), 8.26 (d, J ) 8.0, 4H,
phenylene-H), 8.86 (d, J ) 5.0, 4H, â-H), and 8.90 (s+d,
4H+2H, â-H); MS m/z ) 2466 (Calcd 2466 for C167H170F6N8S2).
UV-vis (THF): λmax(log ꢀ) ) 420 (6.1), 516 (4.8), 552 (4.7), 597
(4.7), and 649 (4.7). Fluorescence (THF): λmax ) 650 and 718
nm.
Closed F or m of Dith ien yleth en e 26c. A solution of 26
in THF was irradiated with UV light (330 nm) for 5 min. The
solvent was removed under reduced pressure, and the residue
was purified by column chromatography (dichloromethane/
hexane) to isolate 26c as a blue solid. 26c: mp 92.5-95.8 °C;
1H NMR (CDCl3, 500 MHz) δ 2.18 (s, 6H, thiophene-CH3), 3.23
(s, 2H, ethynyl-H), 6.69 (s, 2H, thiophene-H), and 7.53 (s, 8H,
phenylene-H); FTIR (KBr, cm-1) 3302, 3033, 2926, 2107, 1491,
1341, 1125, 657, 628; MS m/z ) 568 (Calcd 568 for C31H18F6S2).
Anal. Calcd for C31H18F6S2: C, 65.48; H, 3.19. Found: C, 65.21;
H, 3.46.
Closed F or m of Dip or p h yr in 6c. Air was removed from
a solution of 26c (11 mg, 19 µmol) and 10-bromo-5,15-bis(3,5-
dioctyloxyphenyl)porphine (45 mg, 43 µmol) in 10 mL of Et3N
by blowing argon for 10 min. Then, Pd2(dba)3 (4 mg, 4 µmol)
and AsPh3 (13 mg, 42 µmol) were added, and the mixture was
stirred at 45 °C for 20 h. The solvent was removed under
reduced pressure, and the residue was filtered through a short
plug of silica gel eluting with dichloromethane. The solvent
was evaporated, and the residue was purified by column
chromatography (dichloromethane/hexane) to yield porphyrin
dimer 6c (36 mg, 14 µmol, 74%). 6c: 1H NMR (CDCl3, 500
MHz) δ -2.53 (s, 4H, NH), 0.88 (t, J ) 7.0, 12H, octyl-8), 1.29
(m, 64H, octyl-4,5,6,7), 1.54 (m, 16H, octyl-3), 1.90 (m, 16H,
octyl-2), 2.33 (s, 6H, thiophene-CH3), 4.16 (t, J ) 7.0, 16H,
octyl-1), 6.88 (s, 2H, thiophene-H), 6.93 (s, 4H, Ph-H), 7.40 (d,
J ) 2.5, 8H, Ph-H), 7.81 (d, J ) 8.0, 4H, phenylene-H), 8.09
(d, J ) 8.5, 4H, phenylene-H), 9.06 (d, J ) 4.5, 4H, â-H), 9.12
(d, J ) 5.0, 4H, â-H), 9.27 (d, J ) 4.5, 4H, â-H), 9.80 (d, J )
4.5, 4H, â-H), and 10.16 (s, 2H, meso-H); MS m/z ) 2515 (Calcd
2513 for C159H186F6N8O8S2). UV-vis (THF): λmax(log ꢀ) ) 428
(5.5), 525 (4.6), 582 (4.7), 611 (4.8), and 677 (4.9). Fluorescence
(THF): λmax ) 663 and 736 nm.
Dip or p h yr in 5. A degassed solution of 21 (27 mg, 65 µmol)
and 10-bromo-5,15-bis(3,5-dioctyloxyphenyl)porphine (27) (137
mg, 130 µmol) in 20 mL of Et3N were added Pd2(dba)3 (12 mg,
13 µmol) and AsPh3 (40 mg, 130 µmol). The resulting mixture
was stirred at 50 °C for 20 h. The solvent was removed under
reduced pressure, and the residue was filtered through a short
plug of silica gel eluting with dichloromethane. The solvent
was evaporated, and the residue was purified by column
chromatography (dichloromethane/hexane) to yield diporphy-
rin 5 (98 mg, 41 µmol, 64%). 5: 1H NMR (CDCl3, 500 MHz) δ
-2.55 (s, 4H, NH), 0.87 (t, J ) 7.0, 12H, octyl-8), 1.28 (m, 64H,
octyl-4,5,6,7), 1.53 (m, 16H, octyl-3), 1.88 (m, 16H, octyl-2), 2.25
(s, 6H, thiophene-CH3), 4.15 (t, J ) 6.5, 16H, octyl-1), 6.91 (s,
4H, Ph-H), 7.39 (d, J ) 2.0, 8H, Ph-H), 7.82 (s, 2H, thiophene-
H), 9.06 (d, J ) 4.5, 4H, â-H), 9.11 (d, J ) 4.5, 4H, â-H), 9.26
(d, J ) 4.5, 4H, â-H), 9.73 (d, J ) 4.5, 4H, â-H), and 10.16 (s,
2H, meso-H); MS m/z ) 2364 (Calcd 2361 for C147H178F6N8O8S2).
UV-vis (THF): λmax(log ꢀ) ) 437 (5.7), 526 (4.5), 572 (4.7), 604
(4.1), and 663 (4.3). Fluorescence (THF): λmax ) 664 and 735
nm.
Dip or p h yr in 6. A degassed solution of 26 (28 mg, 49 µmol)
and 10-bromo-5,15-bis(3,5-dioctyloxyphenyl)porphyrin (27) (100
mg, 95 µmol) in 20 mL of Et3N were added Pd2(dba)3 (9 mg,
10 µmol) and AsPh3 (31 mg, 101 µmol). The resulting mixture
was stirred at 45 °C for 20 h. The solvent was removed under
reduced pressure, and the residue was filtered through a short
plug of silica gel eluting with dichloromethane. The solvent
was evaporated, and the residue was purified by column
chromatography (dichloromethane/hexane) to yield diporphy-
rin 6 (80 mg, 32 µmol, 64%). 6: 1H NMR (CDCl3, 500 MHz) δ
-2.55 (s, 4H, NH), 0.86 (t, J ) 7.0, 12H, octyl-8), 1.28 (m, 64H,
octyl-4,5,6,7), 1.54 (m, 16H, octyl-3), 1.88 (m, 16H, octyl-2), 2.09
(s, 6H, thiophene-CH3), 4.15 (t, J ) 7.0, 16H, octyl-1), 6.91 (s,
4H, Ph-H), 7.39 (d, J ) 2.0, 8H, Ph-H), 7.50 (s, 2H, thiophene-
H), 7.79 (d, J ) 8.0, 4H, phenylene-H), 8.07 (d, J ) 8.5, 4H,
phenylene-H), 9.05 (d, J ) 4.5, 4H, â-H), 9.10 (d, J ) 4.5, 4H,
â-H), 9.26 (d, J ) 4.5, 4H, â-H), 9.80 (d, J ) 4.5, 4H, â-H), and
Ack n ow led gm en t. This work was partly supported
by a Grant-in Aid for Scientific Research (No. 11133230
and 11740350) from Ministry of Education, Science,
Sports and Culture of J apan.
Note Ad d ed in P r oof. After submission of this paper,
we were informed by one of the referees that a com-
munication existed on a similar matter. Norsten, T.;
Branda, N. J . Am. Chem. Soc. 2001, 123, 1784.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
1, 2, 3, 4, 4c, 5, 6, and 6c. This material is available free of
charge via the Internet at http://pubs.acs.org.
J O010001P