Substitution effects of C≡C triple bonds on the fluorescent properties of perylenes studied by emission and transient absorption measurements

Article abstract of DOI:10.1016/j.cplett.2012.03.108

Perylenes substituted with trimethylsilylethynyl, tert-butylethynyl and trimethylsilylbutadiynyl groups were prepared, and their photophysical and photochemical properties were investigated through measurements of fluorescence yields, lifetimes, and tripl

Full text of DOI:10.1016/j.cplett.2012.03.108

Chemical Physics Letters 536 (2012) 72–76
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Substitution effects of C„C triple bonds on the fluorescent properties of
perylenes studied by emission and transient absorption measurements
Minoru Yamaji , Hajime Maeda b, , Yasuaki Nanai , Kazuhiko Mizuno
a,
⇑
⇑
b
b,
⇑
a
Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University, Kiryu, Gunma 376-8515, Japan
Department of Applied Chemistry, Graduate School of Engineering, Osaka Prefecture University, Sakai, Osaka 599-8531, Japan
b
a r t i c l e i n f o
a b s t r a c t
Article history:
Perylenes substituted with trimethylsilylethynyl, tert-butylethynyl and trimethylsilylbutadiynyl groups
were prepared, and their photophysical and photochemical properties were investigated through mea-
surements of fluorescence yields, lifetimes, and triplet–triplet absorption. Introduction of these groups
caused little change in the rates of fluorescence, but decreased the fluorescence yields and substantially
enhanced the rates of non-radiative processes. Observation of the triplet absorption was evident for the
origin of the enhanced non-radiative process by the substitution with the triple bond(s).
Ó 2012 Elsevier B.V. All rights reserved.
Received 20 February 2012
In final form 28 March 2012
Available online 4 April 2012
1
. Introduction
in the fluorescence yields of these compounds has not been revealed
in detail. To understand the effect of ethynyl groups or C„C triple
It is known that deactivation from lowest excited singlet states
1
(S ) of aromatic compounds in solution proceeds via three compet-
bond on excited aromatic compounds, systematic investigations
are necessary based on the photophysical parameters for the deacti-
vation processes from the fluorescent states.
itive photophysical pathways, fluorescence, internal conversion (IC)
to the ground state (S ) and intersystem crossing (ISC) to the lowest
triplet state (T ) [1,2]. Recently, a number of synthetic studies of si-
0
Perylene, which is one of prototype aromatic compounds, is well
known to exhibit the large fluorescence yield of ca. 0.9 and the fluo-
rescence lifetime of 6 ns along with a small triplet yield (ꢀ0.01) [26].
Because of the large fluorescence yield, perylene was used, for
example, as a core molecule of a dendrimer to investigate the mech-
anism of Förster-type energy transfer [27], and as a fluorescent
probe tethered with a C„C triple bond to DNA bases [28–30]. To
our best knowledge, no photophysical and photochemical investi-
gations of silylated perylene derivatives have been reported. Thus,
it is of our interest to know how efficiently introducing silylethynyl
groups to the perylene skeleton enhances the fluorescence yields. In
the present work, we prepared a series of perylenes with trimethyl-
silylethynyl (TMSE), tert-butylethynyl (BuE) and trimethylsilylbut-
adiynyl (TMSB) groups (Chart 1). The fluorescence spectra, yields,
lifetimes, and triplet absorption spectra of these compounds were
measured in solution. Based on the photophysical parameters of
the rates of fluorescence and nonradiative processes, the effects of
these substituent groups on the fluorescence states were studied.
In the text, character for the transition moments in the excited sin-
glet states of the perylene derivatives used in the present work is ex-
1
lyl-substituted aromatic compounds have been reported for devel-
oping high-yield fluorescent materials [3–19]. The increase in the
fluorescence yield can be explained in two manners [20]. One is that
silyl substitution stabilizes the S
than the second triplet (T ) state. Therefore, the ISC rate can be re-
garded negligibly small compared to those of other processes. Some
aromatic compounds have negligible rates of IC from the S to the S
1
state so that it is lowered in energy
2
1
0
states [5,6,21]. In these cases, a considerable increase in the fluores-
cence yield is expected. The other is that introduction of silyl groups
into fused aromatic systems causes a bathochromic shift, which in-
creases the molar absorption coefficients (
e) of the resultant sys-
tems. The fluorescence rate constants (k ) are linearly related to
f
e
by the Strickler–Berg equation [22], and substitution with silyl
groups, such as trialkylsilyl and triphenylsilyl groups, considerably
increases the fluorescence rates or quantum yields [12,14,19,23].
Silylethynyl groups have been introduced to condensed aromatic
skeletons, such as anthracene [23–25], pentacene [9] and pyrene
[
17]. These compounds show intense fluorescence compared to
1
1
the parent aromatic compounds. The mechanism for the increase
pressed as L
. Experimental section
.1. Instruments
a b
and L with the directions shown in Chart 2.
2
⇑
Corresponding authors. Present address: Division of Material Sciences, Gradu-
ate School of Natural Science and Technology, Kanazawa University, Kanazawa 920-
2
1
2
192, Japan. Fax: +81 76 234 4800 (H. Maeda), +81 277 301212 (M. Yamaji), +81 72
549289 (K. Mizuno).
Absorption spectra were recorded on
a JASCO Ubest 50
E-mail addresses: yamaji@gunma-u.ac.jp (M. Yamaji), maeda-h@t.kanazawa-
u.ac.jp (H. Maeda), mizuno@chem.osakafu-u.ac.jp (K. Mizuno).
spectrophotometer. Emission spectra were recorded on a Hitachi
0
009-2614/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.cplett.2012.03.108

M. Yamaji et al. / Chemical Physics Letters 536 (2012) 72–76
73
R
sion measurement and laser photolysis were adjusted to achieve
optical densities of less than 0.2 and 1.0, respectively, at the exci-
tation wavelength.
tBu (BuE),
C
R = H,
C
C
C
SiMe3 (TMSE) and
2.3. Compound preparation
C
C C
C SiMe (TMSB)
3
2.3.1. 3-(3,3-Dimethylbut-1-ynyl)perylene (BuEPer)
To a round-bottom flask equipped with a dropping funnel and a
Chart 1. The molecular structure of perylenes used in the present work.
magnetic stirrer, perylene (1.02 g, 4.0 mmol) and DMF (180 mL)
were placed. The mixture was stirred at room temperature until
all perylene solid was dissolved. DMF (20 mL) solution of N-bromo-
succinimide (712 mg, 4.0 mmol) was slowly added, and the solu-
Fluorescence Spectrometer F-7000. Nanosecond fluorescence life-
times (s ) were determined using a time-correlated single-photon
f
2
tion was stirred for 24 h at room temperature. H O was added to
counting fluorimeter (FL-900CDT, Edinburgh Analytical Instru-
ments). Picosecond fluorescence lifetimes were determined with
the third harmonics (266 nm) from a femtosecond laser system
equipped with a mode-locked Ti:sapphire laser (Tsunami, Spectra
Physics), which had a center wavelength of 800 nm, pulse width
of 70 fs, and repetition rate of 82 MHz, with a CW green laser
give golden solid, which was collected by suction filtration. The
crude solid (1.40 g, ca. 80% yield) was assigned to 3-bromoperyl-
ene, but it contained small amount of dibromoperylenes by 1
H
NMR analysis. Data for 3-bromoperylene (after recrystallization
1
from toluene): golden solid; mp 245–247 °C; H NMR (300 MHz,
CDCl
.59 (dd, J = 8.1, 7.8 Hz, 1H), 7.71 (d, J = 8.4 Hz, 2H), 7.77 (d,
J = 8.0 Hz, 1H), 8.00 (d, J = 8.4 Hz, 1H), 9.15 (d, J = 8.7 Hz, 1H),
0.31 (s, 1H) ppm. To an argon-purged, round-bottom flask
3
) d 7.48 (dd, J = 8.1, 7.6 Hz, 1H), 7.49 (dd, J = 8.0, 7.7 Hz, 1H),
(
532 nm, 4.5 W, Millenia V, Spectra Physics) for pumping. The exci-
7
tation and detection systems for obtaining the time profile of fluo-
rescence are detailed elsewhere [31]. The fluorescence lifetime and
transient absorption measurements were carried out at 295 K. The
1
equipped with a Dimroth condenser and a magnetic stirrer, a part
of the crude 3-bromoperylene (103 mg, 0.31 mmol), 3,3-dimethyl-
fluorescence quantum yields (
f
U ) were determined by using an
absolute luminescence quantum yield measurement system
1
-butyne (0.3 mL, 2.4 mmol), CuI (21 mg, 0.11 mmol), Pd(PPh
3 4
)
(
(
C9920-02) from Hamamatsu Photonics [32]. The fourth harmonics
266 nm) of a Nd :YAG laser (JK Lasers HY-500; pulse width 8 ns)
(
30 mg, 0.030 mmol), Et N (5 mL) and THF (10 mL) were placed.
3
3
+
The solution was heated to 80 °C and stirred vigorously for 15 h
was used as the light sources for flash photolysis. The number of
laser pulses in each sample was less than four to avoid excess
exposure. The details of the detection system for the time profiles
of the transient absorption have been reported elsewhere [33]. The
transient absorption spectra were obtained using an USP-554 sys-
tem from Unisoku, which provides a transient absorption spectrum
with one laser pulse. Melting points were determined on a Yana-
under reflux. Solvents were removed by evaporation. Purification
by column chromatography on silica gel (eluent: CHCl
ane = 1/4) followed by HPLC (GPC, eluent: CHCl ) and recrystalliza-
tion from EtOH gave 3-(3,3-dimethylbut-1-ynyl)perylene (BuEPer,
3
/hex-
3
6
2
7
9 mg, 67% yield). Data for BuEPer: golden crystals; mp 253–
1
3
55 °C; H NMR (300 MHz, CDCl ) d 1.44 (s, 9H), 7.47 (dd, J = 8.1,
.6 Hz, 1H), 7.47 (dd, J = 7.7, 7.6 Hz, 1H), 7.52–7.56 (m, 2H), 7.67
1
gimoto Micro Melting Point apparatus (Yanaco MP-500). H and
(
d, J = 7.6 Hz, 2H), 8.09 (d, J = 7.8 Hz, 1H), 8.14–8.23 (m, 4H) ppm;
C NMR (75 MHz, CDCl ) d 1.5, 28.8, 31.5, 104.9, 119.6, 120.4,
3
1
3
C NMR spectra were recorded on a Varian MERCURY-300
300 MHz and 75 MHz, respectively) spectrometer using Me Si as
an internal standard. IR spectra were recorded on a Jasco FT/IR-
30 spectrometer.
13
(
4
1
1
20.6, 121.2, 126.2, 126.5, 126.6, 126.9, 127.8, 128.0, 128.49,
28.50, 130.5, 130.8, 130.9, 131.1, 131.3, 134.6, 134.7 ppm; IR
2
ꢁ1
(
KBr)
m
2966, 827, 809, 767 cm
.
2
.3.2. 3-(Trimethylsilylethynyl)perylene (TMSEPer)
To an argon-purged, round-bottom flask equipped with a Dim-
2.2. Materials and samples
roth condenser and a magnetic stirrer, the crude 3-bromoperylene
Cyclohexane (CH, spectroscopic grade from Sigma-Aldrich),
(
(
(
337 mg, 1.0 mmol), trimethylsilylacetylene (1 mL, 7.1 mmol), CuI
11 mg, 0.058 mmol), Pd(PPh (40 mg, 0.035 mmol), Et
40 mL) and DMF (10 mL) were placed. The solution was heated
methylcyclohexane (Uvasol from Dojin) and isopentane (UV-spec-
troscopy grade from Fluka) were used as supplied. CH was used as
the solvent at 295 K whereas a mixture of methylcyclohexane and
isopentane (3:1 v/v) was used as a matrix for the phosphorescence
measurement at 77 K. Perylene from Wako was purified by re-
peated sublimations in vacuum. All the samples for fluorescence
and transient absorption measurements were degassed in a quartz
cell with a 1 cm path length by several freeze-pump-thaw cycles
on a high vacuum line. The concentrations of the samples for emis-
3
)
4
3
N
to 80 °C and stirred vigorously for 24 h under reflux. Conc. HCl
was added until the solution was neutralized. CHCl and saturated
NH Cl aqueous solution were added and shaken. The organic phase
was separated, dried over Na SO , filtered, and evaporated. Purifi-
cation by column chromatography on silica gel (eluent: CHCl ) fol-
lowed by HPLC (GPC, eluent: CHCl ) and recrystallization from
hexane/CHCl gave 3-(trimethylsilylethynyl)perylene (TMSEPer,
83 mg, 52% yield). Data for TMSEPer: yellow solid; mp 246–
3
4
2
4
3
3
3
1
2
9
1
48 °C; H NMR (300 MHz, CDCl
3
) d 0.35 (s, 9H), 7.49 (dd, J = 7.7,
1La (S - S )
0
1
.3 Hz, 2H), 7.59 (dd, J = 8.2, 7.9 Hz, 1H), 7.68–7.72 (m, 3H), 8.12
1
3
(
d, J = 8.1 Hz, 1H), 8.18–8.23 (m, 4H) ppm; C NMR (75 MHz,
CDCl ) d 0.8, 100.9, 103.7, 119.6, 120.3, 120.8, 121.2, 126.4,
3
1
26.8, 127.5, 128.2, 130.9, 131.2, 132.1, 134.8, 134.8 ppm; IR
1
ꢁ1
L (S - S )
(KBr)
m
2146 (C„C), 898, 858 (SiMe
3
) cm
.
b
0
2
2.3.3. 3-(Trimethylsilylbutadiynyl)perylene (TMSBPer)
To a round-botom flask equipped with a magnetic stirrer,
-(trimethylsilylethynyl)perylene (TMSEPer, 380 mg, 0.43 mmol),
3
4
n-Bu NF (TBAF, 1 mL, 1.0 mmol) and THF (40 mL) were placed.
Chart 2. The direction of the transient moments in the excited singlet states of
perylene.
The solution was stirred for 4 h at room temperature. After solvent

7
4
M. Yamaji et al. / Chemical Physics Letters 536 (2012) 72–76
was removed by evaporation, residue was purified by column chro-
matography on silica gel (eluent: CHCl ) followed by recrystalliza-
tion from hexane/CHCl to give 3-ethynylperylene (110 mg, 93%
yield). Data for 3-ethynylperylene: brown solid; mp >300 °C;
NMR (300 MHz, CDCl ) d 3.55 (s, 1H), 7.50 (dd, J = 7.4, 7.6 Hz, 2H),
3
3
1
H
3
7
.58 (dd, J = 7.8, 7.8 Hz, 2H), 7.69–7.73 (m, 3H), 8.13 (d, J = 8.1 Hz,
1
H), 8.18–8.26 (m, 4H) ppm. To a round-botom flask equipped with
a magnetic stirrer, 3-ethynylperyrene (131 mg, 0.47 mmol), CuI
68 mg, 0.47 mmol), trimethylsilylacetylene (0.5 mL, 3.5 mmol),
tetramethylethylenediamine (TMEDA, 3 mL) and CH Cl (30 mL)
(
2
2
were placed. The solution was stirred for 5.5 h at room temperature.
The solution was filtered using celite. Purification by column chro-
matography on silica gel (eluent: hexane/CHCl
lowed by HPLC (GPC, eluent: CHCl ) and recrystallization from
hexane/CHCl gave 3-(trimethylsilylbutadiynyl)perylene (TMSB-
Per, 73 mg, 42% yield). Data for TMSBPer: red solid; mp 260–
3 f
= 4/1, R = 0.76) fol-
3
3
1
2
7
1
3
62 °C; H NMR (300 MHz, CDCl ) d 0.29 (s, 9H), 7.49 (dd, J = 8.0,
.6 Hz, 1H), 7.50 (dd, J = 7.9, 7.8 Hz, 1H), 7.58 (dd, J = 8.1, 7.7 Hz,
H), 7.70–7.73 (m, 3H), 8.10 (d, J = 8.4 Hz, 1H), 8.16–8.25 (m, 4H)
1
3
ppm; C NMR (75 MHz, CDCl
3
) d 0.2, 75.8, 80.0, 88.2, 92.6, 118.2,
19.5, 120.8, 120.9, 121.4, 125.9, 126.6, 126.7, 127.6, 128.2, 128.4,
28.8, 130.4, 130.8, 131.6, 132.9, 134.5, 135.4 ppm; IR (KBr)
1
1
(
m
.
ꢁ
1
C„C) 2193, (C„C) 2097, (Si–Me) 1388, 1251, 864, 843, 809 cm
. Results and discussion
.1. Absorption and fluorescence properties of the perylenes
Figure 1 shows absorption and fluorescence spectra of perylene
3
3
Figure 1. Absorption (solid) and fluorescence (blue or dash) spectra of perylene (a),
BuEPer (b), TMSEPer (c) and TMSBPer (d) in cyclohexane. (For interpretation of the
references to color in this figure legend, the reader is referred to the web version of
this article.)
and the derivatives with TMSE, BuE and TMSB groups. All the
absorption and emission spectra showed well-resolved vibrational
structures. The measured fluorescence excitation spectra were
found to agree with the corresponding absorption spectra. The ori-
gins of the absorption and fluorescence spectra were clearly seen.
On increasing the number of the triple bond in the substituent
6
8 ꢁ1
f
group, the knr value increased from 10 to 10 s while the k value
8
ꢁ1
showed only a little change (2 ꢂ10 s ). Between the ethynyl-
substituted perylenes (BuEPer and TMSEPer), appreciable differ-
ences in the k and k values were not detected, which indicates
The S
1
0
S character of perylene in the wavelength domain,
1
3
50–450 nm is due to the L
a
transition whereas the S
2
0
S char-
1
f
nr
acter due to the L
b
transition is located in the shorter wavelength
that the presence of the terminating groups (TMS and tert-butyl)
does not influence to these rates. The k value is closely related
region. The shapes of the absorption and fluorescence spectra of
the perylene derivatives were similar to those of perylene. Thus,
f
to the direction and the magnitude of the transition moment. In
the character of the S
also can be regarded as that of the L
spectra were mirror-imaged by the 1L
1
0
S transition of the perylene derivatives
1
1
light of the obtained k values, the La transition moment does
f
a
transition. The fluorescence
absorption band. The S
not seem to be influenced by introduction of TMSE, BuE and TMSB
groups at the 3-position of the perylene skeleton. On the other
hand, the nonradiative processes, which consist mostly of internal
conversion (IC) to the ground state and intersystem crossing (ISC)
to the triplet states, are definitely enhanced by the introduction
with the triple bonds.
a
1
state energies (E ) of the compounds were determined from the
S
averaged energies of the origins of the corresponding absorption
and fluorescence spectra. These values are listed in Table 1 along
with the fluorescence yields (
with the triple-bonded group(s), the
to that of peryrene (0.98). It is notable that the number of the triple
bond substantially influenced the value, although the did not
appreciably vary by the substitution. Change of the terminating
groups from TMS to Bu does not seem to affect the and values.
The obtained E values tend to decrease upon introduction of the
U
f
) and lifetimes (
f
s ). On substituting
U
f
values decreased compared
3.2. Observation of the triplet formation on transient absorption
U
f
s
f
measurements
U
f
s
f
In the present work, the ISC process was examined by observ-
ing the triplet–triplet (T–T) absorption using flash photolysis
techniques. Figure 2 shows the transient absorption spectra ob-
tained at 500 ns upon laser photolysis of CH solutions of peryl-
enes. A very weak transient absorption spectrum was obtained
for perylene in the wavelength region of 430–560 nm. The inten-
S
triple bond(s). Phosphorescence from perylene and the derivatives
were not observed at 77 K in the wavelength region 500–700 nm
with our instrument.
The quantum yields (
Unr) of the nonradiative deactivation of
the studied compounds were estimated by using Eq. (1) and
f
U .
T
sities of all the transient absorption decreased with lifetimes (s )
U
nr ¼1 ꢁ
U
f
ð1Þ
and
of a few tens of microseconds (see Table 1), and the decay was
accelerated in the presence of the dissolved oxygen. Based on
these observations, the obtained transient signals could be as-
cribed to the triplet–triplet (T–T) absorption of the corresponding
perylene compounds. The molar absorption coefficient of triplet
Based on these quantum yields, the corresponding rates (k
f
knr) were, respectively, estimated with Eqs. (2) and (3) using the
s
f
values.
ꢁ
1
k
f
¼
U
f
s
ð2Þ
ð3Þ
3
ꢁ1
ꢁ1
f
perylene in CH is reported to be 13000 dm mol cm
80 nm [34]. The wavelengths of maximum absorption (kmax
for the T–T absorption spectra are listed in Table 1. The intensity
at
)
T–T
4
ꢁ
nr
U s
f
1
k
nr
¼

M. Yamaji et al. / Chemical Physics Letters 536 (2012) 72–76
75
Table 1
Photophysical parameters obtained for pyrene and perylene derivatives in the present work.
c
f
f2
TT
Compound
e
(
E
S
U
f
s
f
k
(10
f
U
nr
k
nr
R
k
max
s
T
104 dm3 mol cm )a
ꢁ1
ꢁ1
(kcal mol )b
ꢁ1
(ns)d
6
s
ꢁ1
)e
(10
4.2
21
6
s
ꢁ1
)g
(10 cm )h
4
ꢁ2
(nm)i
(l
s)j
Perylene
BuEPer
TMSEPer
TMSBPer
1.95 (435)
4.02 (455)
3.84 (459)
4.40 (470)
65.2
62.2
61.7
60.2
0.98
0.91
0.88
0.51
4.7
4.3
4.2
2.2
209
212
210
232
0.02
0.09
0.12
0.49
2.04
2.66
4.25
4.45
480
515
520
545
5000k
23.0
13.5
12.0
29
223
a
b
c
d
e
f
The molar absorptivities at the wavelength, k nm.
The lowest excited singlet state energies estimated from the origins of absorption and fluorescence spectra.
Fluorescence quantum yields at 295 K.
Fluorescence lifetimes in cyclohexane at 295 K determined by the photon counting method.
ꢁ1
Fluorescence rates estimated by the equation, k
Estimated by the equation,
Rates of non-radiative processes were determined by the equation, knr
Sum of the squared spin-orbit coupling constant (f) values.
f
=
U
f
s
f
.
Unr = 1 ꢁ
f
U .
g
h
i
fꢁ1
.
=
U
nr
s
Wavelengths of the maximum absorbance of the triplet-triplet absorption in cyclohexane at 295 K.
Lifetimes of the triplet states in cyclohexane at 295 K.
Data from Ref. [26]. The transient signal of triplet perylene was too weak to determine the decay lifetime in this work.
j
k
Hamiltonian (HSO) can be expressed with the use of the angular-
and spin-momentum operators (l and s, respectively) and the
spin-orbit coupling constant (f), which gives a measure for the
heavy atom effect.
0.01
(a)
0
H
SO ¼fðl ꢃsÞ
ð5Þ
Eq. (4) can then be rewritten as follows:
0
.02
(b)
X
2
2
k
isc
¼
qf ꢃhT
f
jl ꢃsjS
i
i ꢃF ꢃf
ð6Þ
0
Here, the f values for C, H and Si atoms are known to be 32, 0.24
ꢁ1
2
and 130 cm , respectively [26]. The sums (
Rf ) of the squared f
(
c)
values for all the compounds used in the present work are listed
0
.02
0
2
2
4
ꢁ2
in Table 1. The ratios of
R
f
for TMSEPer (
R
f = 4.25 ꢂ10 cm
against perylene
f = 2.04 ꢂ10 cm ) were estimated to be 2.1 and 1.3, respec-
tively. The knr values of TMSEPer, BuEPer and perylene were
)
2
4
ꢁ2
and
BuEPer
(
R
f = 2.66 ꢂ10 cm
)
2
4
ꢁ2
(R
7
7
6 ꢁ1
2
.1 ꢂ10 , 2.9 ꢂ10 and 4.2 ꢂ10 s , respectively. Thus, the esti-
0
.4
2
mated ratios of
Rf do not explain the increase of these knr. It is in-
(d)
ferred from these considerations that the mechanism of ISC
enhanced by the introduction of TMSE and BuE groups cannot be
simply interpreted by Fermi’s golden rule.
0
T
The triplet lifetimes (s ) of perylene derivatives in CH at 295 K
4
00
500
600
showed a few tens microseconds, which were substantially shorter
than that of perylene (5 ms [26]). The decay processes of the triplet
state generally consist of ISC to the ground state and phosphores-
cence emission. Phosphorescence emission of perylenes was not
Wavelength / nm
Figure 2. Transient absorption spectra at 500 ns obtained upon 266-nm laser
pulsing in cyclohexane solutions of perylene (a), BuEPer (b), TMSEPer (c) and
TMSBPer (d) in cyclohexane at 295 K. Absorbance changes in the shorter
wavelength regions for Per and TMSPer were not obtained due to the large
absorption of the original ground state.
observed at 77 K in the present work. Thus, the phosphorescence
0
rate (k
p
) can be regarded negligible compared to the rate ðk Þof
isc
0
ISC from the triplet to the ground state. In this case, the k values
isc
correspond to the reciprocals of
T
s , which are in the order of
4
ꢁ1
1
0 s at 295 K.
of the triplet absorption increased with increasing the number of
the C„C triple bonds. This observation indicates that introduction
of the triple bond enhances the ISC process or increases the rate
It is reported that the 0–0 position of phosphorescence of pery-
ꢁ1
lene in single crystal at 4.2 K is located at 12373 cm
ꢁ1
(35.3 kcal mol ) [35] while the state energies of the second singlet
ꢁ1
(kisc) of ISC. In general, the ISC mechanism is interpreted in terms
2 2
(S ) and triplet (T ) are estimated to be 98.5 and 92.2 kcal mol ,
of the spin-orbit interaction with the kisc value being expressed
by Fermi’s golden rule [2].
respectively, [36]. The T2 state is located at energies much higher
ꢁ1
than that of the S state (65.2 kcal mol ). Although the S absorp-
1
2
1
tion band of perylene due to the L
b
transition is not clearly seen,
X
2
those of the derivatives appear in the wavelength region,
k
isc
¼
qf ꢃhT
f
jHSOjS
i
i ꢃF
ð4Þ
ꢁ1
2
80–330 nm (ca. 86 kcal mol from the origin), probably due to
In Eq. (4), |S
i
iand |T
f
iare the wavefunctions for the initial ex-
the disorder of the molecular symmetry. Assuming that the S
2 2
–T
1 1
cited singlet state (S ) and the final triplet state (T ), respectively;
energy gap of perylene is the same in the perylene derivatives,
q
f
is the density of the final state; and HSO and F are the Hamilto-
their T
2
energies would not be smaller than the corresponding S
1
2
ꢁ1
nian for the spin-orbit interaction and the Franck–Condon factor
energies (62–60 kcal mol ). Therefore, no contributions of the T
between the initial and final states, respectively. The perturbation
states of perylenes are expected in the fluorescent features in the

7
6
M. Yamaji et al. / Chemical Physics Letters 536 (2012) 72–76
[2] N.J. Turro, Modern Molecular Photochemistry, The Benjamin/Cummings
S
1
states. In fact, we have found that the k
f
values of perylenes are
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not influenced by the presence of triple bonds.
[
[
[
3] A.G. Evans, B. Jerome, N.H. Rees, J. Chem. Soc., Perkin Trans. 2 (1973) 447.
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4
. Conclusions
(
80) (1984) 383.
[
6] H. Shizuka, Y. Sato, Y. Ueki, M. Ishikawa, M. Kumada, J. Chem. Soc., Faraday
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We prepared perylenes having C„C triple bonds, and investi-
[
[
gated their deactivation properties of the fluorescent state based
on the measurements of the fluorescence yields ( ) and lifetimes
) and triplet absorption. The absorption and fluorescence fea-
tures of these derivatives were the same as those of perylene,
and the k values were not influenced as the number of substitu-
ents increased. It is inferred from these observations that the
U
f
(s
f
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[
[
[
[
f
1
1
L
a
transition of perylenes was not influenced by the presence of
substituted triple bonds. In contrast, based on the transient absorp-
tion measurements, it was found that the ISC process was en-
hanced in proportion to the number of the triple bonds. The
heavy atom effect was not sufficient to explain the trend of this
enhancement. Presumably, other interactions caused by introduc-
ing the triple bonds, such as vibronic coupling of the triple bonds
to the perylene moiety, would be the origins for the increment in
the ISC processes from the fluorescent state to the triplet state
and from the triplet to the ground state. In the present study, how-
ever, we were unable to proceed further investigations in solution.
Bisethynyl- and hexatriynylperylenes could be suitable com-
pounds to understand the C„C triple bonds affecting photophysi-
cal processes of perylenes, which is in progress.
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[
[
[
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Acknowledgements
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[
26] M. Montalti, A. Credi, L. Prodi, M. Teresa, Gandolfi: Handbook of
Photochemistry, third ed., Revised and Expanded, CRC Press, Boca Raton,
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This work was supported by Grants-in-Aid for Scientific Re-
search (KAKENHI) from JSPS (No. 23350059) and the ‘Element
Innovation’ Project by the Ministry of Education, Culture, Sports,
Science, and Technology, Japan (to MY). HM and KM acknowledge
Grant-in-Aids for Scientific Research Scientific Research (KAKENHI)
from JSPS (Nos. 20550049 and 23550047), and Cooperation for
Innovative Technology and Advanced Research in Evolutional
Areas (CITY AREA) program from the Ministry of Education, Cul-
ture, Sports, Science and Technology, Japan. M.Y. thanks Dr. Atsushi
Kobayashi at Gunma University for his assistance on determining
the fluorescence yields with the instrument (C9920-02).
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