Full-color photochromism of a fused dithienylethene trimer

Article abstract of DOI:10.1021/ja051467i

A diarylethene fused trimer, 1-(5-(2-(3,5-dimethyl-2-thienyl)hexafluorocyclopententen-1-yl)-2,4-dimethyl-3-thienyl)-2-(5-(2-(2,4-dimethyl-5-phenyl-3-thienyl)hexafluorocyclopentene-1-yl)-2,4-dimethyl-3-thienyl)hexafluorocyclopentene, was synthesized. The d

Full text of DOI:10.1021/ja051467i

Published on Web 06/04/2005
Full-Color Photochromism of a Fused Dithienylethene Trimer
Kenji Higashiguchi,†,‡ Kenji Matsuda,*,†,§ Naoki Tanifuji,§ and Masahiro Irie*,†
Department of Chemistry and Biochemistry, Graduate School of Engineering, Kyushu UniVersity, and
PRESTO, JST, 6-10-1 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan
Received March 8, 2005; E-mail: irie@cstf.kyushu-u.ac.jp; kmatsuda@cstf.kyushu-u.ac.jp
Light-induced reversible isomerization between two isomers
having different absorption spectra is referred to as photochromism.1
In normal photochromic systems they interconvert between only
two states: “colorless” and “colored”. On the other hand, in
multicolor or multicomponent systems, reversible multimode
switching between more than two states can be realized. In a three-
color system, eight states (23 ) 8) can be produced. The multicolor
system is useful for multifrequency optical memories and displays.
Multicolor systems can be accomplished by mixing photochromic
compounds with different colors in solutions,2a in polymer matrixes,2b
and in single crystals.2c,d
We took an approach to incorporate three photochromic units
in one molecule.3 The advantage of a one-molecule system over
mixture systems is high image resolution, constant color balance
in a large area, and possible application to a multifrequency single-
molecule memory. In previous reports,4,5 nonsymmetric fused
dithienylethene dimers were synthesized, and two-color photo-
chromism was demonstrated. Here we report on a fused trimer,
which undergoes full-color photochromism.
Figure 1 shows the fused trimer along with anticipated photo-
chromic reactions. Fused trimer 1 has three dithienylethene
moieties: bis(2-thienyl)ethene, (2-thienyl)(3-thienyl)ethene, and bis-
(3-thienyl)ethene, with two thiophene rings in common. The yellow
circle in Figure 1 indicates the bis(2-thienyl)ethene moiety, which
is expected to develop yellow color upon cyclization, because the
π-conjugation cannot extend to the rest of chromophores in the
closed-ring isomer.6 The π-conjugation of the closed-ring isomer
of (2-thienyl)(3-thienyl)ethene unit (a red circle) is extended to a
phenyl substituent at the 5-position of the thiophene ring to develop
red color.6 Bis(3-thienyl)ethene unit (a blue circle) would show
blue color upon cyclization because the unit has π-conjugated
substituents at the 5-positions of the thiophene rings.7
Figure 1. Photochromic reactions of dithienylethene 1. Red line denotes
the expansion of the π-conjugation.
The synthesis of 1a8 was carried out starting from 3-bromo-2,4-
dimethyl-5-trimethylsilylthiophene.9 The synthesized compound was
confirmed by NMR and mass spectroscopy. Compound 1a was
recrystallized from hexane. X-ray crystallographic analysis also
confirmed the molecular structure.10
Upon irradiation with 313-nm light, the colorless hexane solution
of 1a turned orange via yellow. Upon further irradiation with UV
light, the solution turned black. When UV (313 nm) and blue (460
nm) light was simultaneously irradiated, the solution turned sky
blue. When the solution was irradiated with UV (313 nm) and red
(633 nm) light, the solution turned red-orange. The solution changed
to yellow when the solution was irradiated with UV (313 nm) and
yellow (578 nm) light. 1 can develop blue, red, and yellow colors
upon irradiation with appropriate wavelength of light, suggesting
that all of the three diarylethene moieties cyclized upon irradiation.
Figure 2. Colors of the open-ring isomer 1a and the isolated closed-ring
isomers 1b-d in hexane solution.
HPLC analysis of the photoirradiated solution indicated the
formation of four colored species. The molecular structure of the
four colored species were determined by absorption spectra as the
closed-ring isomer of the central bis(3-thienyl)ethene moiety (1b),
the terminal (2-thineyl)(3-thienyl)ethene moiety (1c), and the
terminal bis(2-thienyl)ethene moiety (1d) for blue, red, and yellow
ones, respectively. Figure 2 shows the colors of the three species.
Additionally, an orange compound was obtained and identified as
the double closed-ring isomer 1e. The color is due to the closed-
ring isomer of the (2-thienyl)(3-thienyl)ethene and bis(2-thienyl)-
ethene units.
† Kyushu University.
‡ Present address: Department of Life Sciences, Graduate School of Arts and
Sciences, the University of Tokyo, 3-8-1 Komaba, Meguro-ku, Tokyo 153-
8902, Japan.
§ PRESTO, JST.
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10.1021/ja051467i CCC: $30.25 © 2005 American Chemical Society

C O M M U N I C A T I O N S
tum yield is known not to be affected by the substitution at the
4-position of the thiophene ring.
There are three possible designs for the fused trimers that have
three color components. The yellow, red, or blue components can
be located in the central unit (see Figure S2 in Supporting
Information). The cyclization quantum yield of the central unit was
found to become very small due to the molecular distortion. To
increase the conversion of the central unit, the unit should have
low cycloreversion quantum yield. Among the three color compo-
nents, the blue-developing unit has the lowest cycloreversion
quantum yield. This is the reason blue-developing bis(3-thienyl)-
ethene moiety was placed in the central unit.
Figure 3. (a) Absorption spectra of 1a and the isolated closed-ring isomers
1b-e in hexane solution: 1a (s, black), 1b (- - -, blue), 1c (- - - , red),
1d (- ‚ -, yellow), and 1e (‚‚‚, green). (b) Decay of the open-ring isomer
1a (2, black) and formation of the closed-ring isomer 1b (1, blue), 1c (9,
red), 1d (b, yellow), and 1e ([, green) upon irradiation with 313-nm light.
The solid lines were least-squares fitting of the concentrations.
In conclusion, a fused dithienylethene derivative 1a was syn-
thesized, and its photochromic performance was examined. It was
revealed that 1a showed full-color photochromic performance by
choosing appropriate wavelengths of light.
Figure 3a shows the spectra of the open-ring isomer 1a and
isolated closed-ring isomers 1b-e. The absorption peaks of 1b-d
are sufficiently separated from each other. All colored species
converted back to the open-ring isomer 1a by irradiation with visible
light (λ > 450 nm). Formation of the closed-ring isomer, in which
adjacent diarylethene units are in the closed-ring form, was not
discerned. This result agreed with the observation of symmetric
dimers and trimer11 and asymmetric fused dimers.5
Acknowledgment. This work was supported by a Grant-in-Aid
for Scientific Research (S) (No. 15105006) from Japan Society of
the Promotion of Science and by PRESTO, JST.
Supporting Information Available: Experimental procedures,
synthesis of 1a, crystallographic data of 1a, and details of the analysis
of the quantum yield (PDF). X-ray structural data for 1a (CIF). This
material is available free of charge via the Internet at http://pubs.acs.org.
A hexane solution containing 1a was irradiated with 313-nm
light, and changes in concentrations of 1a-e were monitored by
HPLC (Figure 3b). At the initial stage of photoirradiation, 1d was
efficiently formed. In the photostationary state, however, the
amounts of 1d and 1e became almost the same. Although the
formation of 1b was slow, the conversion gradually increased.
The time course of the formation of the closed-ring isomers 1b-e
and the decrease of the open-ring isomer 1a was analyzed based
References
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:
Φ
1d-1a:Φ1c-1e:Φ1e-1c:Φ1d-1e:Φ1e-1d. The ratio was calculated to be
0.0038:0.022:0.072:0.48:0.14:0.95:1:0.51:0.63:0.60.12 The quantum
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Φ1b-1a, Φ1c-1a, and Φ1d-1a were independently measured in hexane
by irradiation with visible light at each absorption maximum to
give Φ1b-1a ) 0.013, Φ1c-1a ) 0.29, and Φ1d-1a ) 0.57. The ratio
of the quantum yields agreed well with the ratio obtained from the
above simulation. The quantum yields of the rest of the reactions
were determined as follows: Φ1a-1b ) 0.0023, Φ1a-1c ) 0.043,
Φ1a-1d ) 0.085, Φ1c-1e ) 0.60, Φ1e-1c ) 0.30, Φ1d-1e ) 0.38,
Φ1e-1d ) 0.36.
The cyclization quantum yields of the three photochromic units
in the trimer are relatively small compared to the quantum yields
of the component units. This is partly ascribed to the nonradiative
decay due to the relatively large molecular size. X-ray crystal-
lographic analysis revealed that the conformation of the central bis-
(3-thienyl)ethene moiety is in the twisted form. This is the reason
Φ1a-1b () 0.0023) is the smallest among the three cyclization
quantum yields.13
The cycloreversion quantum yield of the cyclohexadiene moiety
at the central unit (Φ1b-1a ) 0.013) is the smallest among the three
units; Φ1c-1a ) 0.29 and Φ1d-1a ) 0.57. It is known that the closed-
ring isomer of bis(3-thienyl)ethene with two phenyl rings at the
5-positions of the thiophene rings has a small cycloreversion
quantum yield.7 The cycloreversion quantum yield of the bis(2-
thienyl)ethene moiety (Φ1d-1a ) 0.57) is similar to the value of
bis(3,5-dimethyl-2-thienyl)ethene (0.58).6 The cycloreversion quan-
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(8) Physical data for compound 1a: mp 167.1-167.9 °C. 1H NMR (400 MHz,
CDCl3): δ 1.4-2.4 (24H, m), 6.44 (1H, s), 7.3-7.4 (5H, m); UV-vis
λmax (ꢀ) 273 nm (2.7 × 104); FAB HRMS (m/z) [M + H]+ calcd for
C45H31F18S4: 1041.1021. Found: 1041.1009.
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C45H30F18S4, FW ) 1040.96,
triclinic P1h, a ) 10.420(2) Å, b ) 11.869(2) Å, c ) 18.348(4) Å, R )
89.164(3)°, â ) 87.914(3)°, γ ) 73.491(3)°, V ) 2174.2(7) Å3, Z ) 2,
R1 ) 0.0639 (I > 2σ), wR2 ) 0.2417 (all data). CCDC 261031. For the
details of the crystallographical result, see Supporting Information.
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