Photoirradiation wavelength dependence of cycloreversion quantum yields of diarylethenes

Article abstract of DOI:10.1039/c4cc00396a

The cycloreversion quantum yields of compounds 1b and 2b increased upon irradiation with light at shorter wavelengths. The irradiation wavelength dependence is ascribed to the energy barrier on the 2A potential energy surface in the excited electronic state.

Full text of DOI:10.1039/c4cc00396a

Showcasing research from Masahiro Irie’s
Laboratory/Department of Chemistry, Rikkyo University,
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Photoirradiation wavelength dependence of cycloreversion
quantum yields of diarylethenes
The cycloreversion quantum yields of photochromic diarylethene
derivatives vary depending on irradiation wavelength of visible
light (450–620 nm). The irradiation wavelength dependence is
ascribed to the energy barrier on the 2A potential energy surface
in the excited electronic state.
See Masahiro Irie et al.,
Chem. Commun., 2014, 50, 3928.
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Photoirradiation wavelength dependence of
cycloreversion quantum yields of diarylethenes†
Cite this: Chem. Commun., 2014,
0, 3928
5
Takaki Sumi, Yuta Takagi, Akira Yagi, Masakazu Morimoto and Masahiro Irie*
Received 17th January 2014,
Accepted 23rd February 2014
DOI: 10.1039/c4cc00396a
www.rsc.org/chemcomm
The cycloreversion quantum yields of compounds 1b and 2b 1-(2-methyl-5-p-cyanophenyl-3-thienyl)-2-(2-methyl-5-p-methoxy-
1
1
increased upon irradiation with light at shorter wavelengths. The phenyl-3-thienyl)perfluorocyclopentene in polymer film.
irradiation wavelength dependence is ascribed to the energy barrier
on the 2A potential energy surface in the excited electronic state.
It is indispensable to verify the wavelength dependence to
explore the reaction mechanism of the 6p electrocyclic reactions
in detail. Here, we report on the results of the measurement of
Photochromism is defined as a reversible transformation of a the wavelength dependence of photocycloreversion quantum
chemical species between two isomers having different absorp- yields of 1,2-bis(2-methyl-1-benzothiophen-3-yl)perfluorocyclo-
tion spectra. The isomers change not only the absorption spectra pentene (1) and 1,2-bis(2,4-dimethyl-5-phenyl-3-thienyl)perfluoro-
but also various physico-chemical properties, such as fluores- cyclopentene (2) (Scheme 1) by using a photoreaction quantum
cence spectra, refractive indices, oxidation–reduction potentials, yield measurement system (Shimadzu, QYM-01) with a corrected
1
–3
and geometrical structures, upon photoirradiation. The photo- power meter, which can provide accurate irradiation photon
chromic switches offer great potential for advancing future optics numbers at a given wavelength. These diarylethene derivatives
and optoelectronics technologies. Among vast numbers of photo- are known to undergo fatigue resistant photochromic reactions;
chromic molecules the most promising ones for the applications the former diarylethene 1 can repeat cyclization/cycloreversion
1
2
are diarylethene derivatives, because of their thermal stability of more than 14000 cycles in n-hexane and the latter diarylethene
4
13
both isomers, rapid response and fatigue resistant property.
2 more than 30000 cycles in the single-crystalline phase.
Fig. 1 shows the absorption spectra of compounds 1 and 2 in
5
According to Kasha’s rule and Vavilov’s law, fluorescence
occurs from the lowest excited electronic state of a given multi- n-hexane. Both compounds were purified by HPLC (eluent:
plicity and the fluorescence quantum yield does not depend on n-hexane; purity 499%). The open-ring isomers 1a and 2a are
the state reached (S , S , S etc.) upon excitation. The quantum colourless in n-hexane. Upon irradiation with UV light the
1 2 3
yields of various photochemical reactions are also anticipated to colourless solutions containing compounds 1a and 2a turn
be invariant so far as the reactions take place via the lowest excited
state, because very rapid vibrational relaxation and internal con-
version occur in and between excited singlet states. Nevertheless
several photochromic reactions have been reported to exhibit
irradiation wavelength dependence of the reaction quantum
6
yields. Notable examples are furylfulgides and diarylethene
derivatives, such as 1,2-bis(2,4,5-trimethyl-3-thienyl)maleic
7
anhydride,
1,2-bis(2-methyl-1-benzothiophen-3-yl)perfluoro-
8
cyclopentene, 1,2-bis-(2-methyl-5-(2-(4-benzoylphenyl)ethen-1-yl)-
-thienyl)perfluorocyclopentene and 1,2-bis(5-(4-ethynylphenyl)-
-methyl-3-thienyl)perfluorocyclopentene
9
3
2
1
0
in solutions and
Department of Chemistry and Research Center for Smart Molecules,
Rikkyo University, 3-34-1 Nishi-Ikebukuro, Toshima-ku, Tokyo 171-8501, Japan.
E-mail: iriem@rikkyo.ac.jp; Fax: +81-3-3985-2397; Tel: +81-3-3985-2397
†
Electronic supplementary information (ESI) available: Materials, instruments,
methods and experimental data. See DOI: 10.1039/c4cc00396a
Scheme 1 Photochromism of diarylethenes 1 and 2.
3
928 | Chem. Commun., 2014, 50, 3928--3930
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The cycloreversion quantum yields (FCO) were measured at
several irradiation wavelengths in the visible region, which are
shown by arrows in Fig. 1. The wavelengths cover the whole region
of the visible absorption bands of the closed-ring isomers. The
quantum yield measurement was carried out as follows. First,
irradiation photon numbers to the sample cell at the irradiation
wavelength were measured by using QYM-01 and the absorption
spectral change upon photoirradiation followed. According to the
following equation, the cycloreversion quantum yields, FCO, at
five wavelengths were determined, shown in Fig. 2.
ꢀ
ꢁ
ꢀ
ꢁ
1
000elnp
NAv
AðtÞ
Að0Þ
log 10
ꢀ 1 ꢀ log 10
ꢀ 1 ¼ ꢀ
FCOt;
where A(t) is the absorbance of the sample at t (sec) time
ꢀ
1
ꢀ1
irradiation, e the absorption coefficient (L mol cm ), l the
cell length (cm), np irradiation photon numbers per second,
3
N Avogadro’s number, and v the solution volume (cm ).
A
log FCO was plotted against wavelengths (expressed in photon
energy), as shown in Fig. 2. The quantum yields increase upon
increasing the irradiation photon energy (see ESI†). The quan-
tum yield of compound 1b at 450 nm is 18% larger than the
value at 580 nm, while the yield of compound 2b at 480 nm is
75% larger than the value at 620 nm. In both compounds 1b
and 2b linear behaviour was observed between log FCO and the
1
1
photon energy, which is typical of energy activated reactions.
The wavelength dependency can be expressed as follows for
compounds 1b and 2b.
ꢀ
5
ꢀ1
Fig. 1 Absorption spectra of (a) 1 (3.6 ꢁ 10 mol L ) and (b) 2 (1.8 ꢁ
ꢀ5
ꢀ1
1
0
mol L ) in n-hexane. Black solid line: open-ring isomer, coloured
Compound 1b: log FCO = ꢀ0.796 + 133/l (nm) (450 nm r
solid line: closed-ring isomer, broken line: photostationary state under
irradiation with 313 nm light. The arrows indicate wavelengths of excitation l r 580 nm)
light used for the cycloreversion quantum yield measurement.
Compound 2b: log FCO = ꢀ2.67 + 526/l (nm) (480 nm r l r
20 nm)
The cycloreversion quantum yields of compounds 1b and 2b
6
red and blue, respectively. The colours are ascribed to the
closed-ring isomers 1b and 2b. The broken lines show the
spectra at the photostationary states under irradiation with
calculated by the above relations at the absorption maxima are
313 nm light. The coloured closed-ring isomers were isolated
by HPLC and their spectra are shown in the figure by red and
blue lines. At the photostationary states upon irradiation with
313 nm light the conversions from the open- to the closed-ring
isomers of compounds 1 and 2 are 47 and 79%, respectively.
The photocyclization quantum yields of compounds 1a and 2a
were determined upon irradiation with 313 nm light. Irradiation
UV wavelength dependence was not measured, because in
the UV region both open- and closed-ring isomers coexist
and precise determination of the yields requires complicated
analysis. The cyclization quantum yields (FOC) of compounds
1a and 2a were measured to be 0.31 and 0.45, respectively
(
(
see ESI†). These values are close to previously reported values
0.35 and 0.46) (Table 1).
Fig. 2 Photoirradiation wavelength dependence of cycloreversion quantum
yields of 1b (red circles) and 2b (blue circles) at 22 1C.
1
4–16
Table 1 Photophysical properties of compounds 1 and 2 in n-hexane
Open-ring isomer
max/nm
Closed-ring isomer
max/nm
l
l
4
ꢀ1
ꢀ1
4
ꢀ1
ꢀ1
(e/10 L mol cm
)
F
OC
(e/10 L mol cm
)
F
CO
1
2
258 (1.52), 289 (0.63), 298 (0.68)
268 (2.84)
0.31
0.45
515 (1.00)
562 (1.09)
log FCO = ꢀ0.796 + 133/l (nm) (450 nm r l r 580 nm)
log FCO = ꢀ2.67 + 526/l (nm) (480 nm r l r 620 nm)
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0 0
-(5 -acetylsulfanyl-2-methyl-5,2 -dithiophen-3-yl)-2-(2-methyl-
,2 -dithiophen-3-yl)perfluorocyclopentene also indicates the
1
5
0
23
presence of the barrier in the excited state energy surface.
In conclusion it was unequivocally verified that the cyclo-
reversion quantum yields of diarylethene derivatives, compounds
1
and 2, are dependent on the irradiation wavelengths and the
dependence correlates with the energy barrier in the excited state
energy surface.
This work was supported by the MEXT-Supported Program
for the Strategic Research Foundation at Private Universities.
Notes and references
1
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2
Fig. 3 Schematic illustration of potential energy surfaces and the cyclo-
reversion reaction path. (c) and (o) mean closed- and open-ring isomers,
respectively.
3
4
5
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6
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1
4–16
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7
1
7–19
According to theoretical calculations
and femtosecond
of 6p electrocyclic systems, the
cycloreversion reaction is considered to proceed as shown in
2
0,21
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9
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1
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1
20,21
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1
6
1
1
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1
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2
2
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2
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The large energy barrier results in a large slope of the photon-
energy dependence of the quantum yield. The temperature
dependence of the cycloreversion quantum yield observed for
2
3930 | Chem. Commun., 2014, 50, 3928--3930
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