Synthesis and spectroscopic study of phenylenee (poly) ethynylenes substituted by amino or amino/cyano groups at terminal(s):Electronic effect of cyano group on charge-transfer excitation of acetylenic φ-systems

Article abstract of DOI:10.1016/j.tet.2010.05.016

To gain insight into substituent electronic effect on charge-transfer excitation of acetylenic p-systems, phenylenee(poly)ethynylenes substituted by Ph₂N or Ph₂N/cyano groups were synthesized by combination of Sonogashira coupling and double elimination protocol of b-substituted sulfones.These substituted phenyleneethynylenes showed large molar absorption coefficients 3, and emitted strong fluorescence upon UV light irradiation.Phenylenee(poly)ethynylenes, which involve butadiyne or hexatriyne motifs, emitted fluorescence in remarkably lower fluorescence quantum yields F_F as their polyethynylene motifs e(C^C)_ne expanded.The drastic decrease of fluorescence quantum yields F_F were explained in terms of increasing nonradiative reaction rate constants k_nr, which had been determined by the corresponding fluorescence quantum yields F _F and lifetime values s.The emission underwent a large bathochromic shift in polar solvents because the charge-separated excited state is more stabilized than the ground state.Comparison of slope values r in Lippert/Mataga plot for the Ph₂N and Ph₂N/cyano-substituted phenylenee(poly)ethynylenes revealed that the latter underwent large change of dipole moments upon photo-excitation although highly expanded acetylenic p-systems with cyano group did little.

Full text of DOI:10.1016/j.tet.2010.05.016

Tetrahedron 66 (2010) 5479e5485
Contents lists available at ScienceDirect
Tetrahedron
journal homepage: www.elsevier.com/locate/tet
Synthesis and spectroscopic study of phenylenee(poly)ethynylenes substituted
by amino or amino/cyano groups at terminal(s): electronic effect of cyano group
on charge-transfer excitation of acetylenic
p-systems
,
,
b
b
b
b
Jing-Kun Fang a c, De-Lie An a , Kan Wakamatsu , Takeharu Ishikawa , Tetsuo Iwanaga , Shinji Toyota ,
*
Shin-ichi Akita c, Daisuke Matsuo c, Akihiro Orita c , Junzo Otera
,
c,
*
*
a Department of Chemistry, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China
b Department of Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005, Japan
c Department of Applied Chemistry, Okayama University of Science, 1-1 Ridai-cho, Kita-ku, Okayama 700-0005, Japan
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 April 2010
Received in revised form 30 April 2010
Accepted 4 May 2010
Available online 8 May 2010
To gain insight into substituent electronic effect on charge-transfer excitation of acetylenic
p-systems,
phenylenee(poly)ethynylenes substituted by Ph2N or Ph2N/cyano groups were synthesized by combi-
nation of Sonogashira coupling and double elimination protocol of -substituted sulfones. These
substituted phenyleneethynylenes showed large molar absorption coefficients , and emitted strong
b
3
fluorescence upon UV light irradiation. Phenylenee(poly)ethynylenes, which involve butadiyne or
hexatriyne motifs, emitted fluorescence in remarkably lower fluorescence quantum yields FF as their
polyethynylene motifs e(C^C)ne expanded. The drastic decrease of fluorescence quantum yields
FF were explained in terms of increasing nonradiative reaction rate constants knr, which had been de-
termined by the corresponding fluorescence quantum yields FF and lifetime values
underwent a large bathochromic shift in polar solvents because the charge-separated excited state is
more stabilized than the ground state. Comparison of slope values in Lippert/Mataga plot for the Ph2N
and Ph2N/cyano-substituted phenylenee(poly)ethynylenes revealed that the latter underwent large
s. The emission
r
change of dipole moments upon photo-excitation although highly expanded acetylenic
cyano group did little.
p-systems with
Ó 2010 Elsevier Ltd. All rights reserved.
1. Introduction
fluorescence from intramolecular charge-separated states,7,8 and
we disclosed that amino-substituted phenylene-(poly)ethynylenes
undergo solvent effect in photoluminescence depending on the
inherent natures of acetylenic modes, which capture negative
charge in the excited states.9 By taking advantage of the intra-
molecular charge-transfer excitation, Yamaguchi and Yoshida suc-
ceeded to tune emission maxima of phenyleneethynylenes without
loss of their high fluorescence quantum yields, which were con-
structed by connecting donor blocks, methoxy-substituted phe-
nyleneethynylenes with acceptor blocks, cyano-substituted
homologs.10 Because these phenyleneethynylenes emit strong
fluorescence in the powdery state, they are promising candidates as
emitting material for organic light-emitting diode (OLED). Recently,
a number of organic sensitizers for photovoltaics have been de-
Acetylenes have attracted extensive attention in material sci-
ences1 such as acetylenic macrocycles2 and polyynes3 because they
possess abundant
p
electrons and rigid arrays. We established
-substituted sulfones for access to
double elimination protocol of
b
acetylenes,4 and disclosed usefulness of this protocol for prepara-
tion of phenyleneethynylene fluorophores.5 It was revealed that
amino-substituted fluorophores emit fluorescence from their
twisted intramolecular charge-transfer states (TICT), when UV light
is irradiated.6 Since the charge-separated excited state is more
stabilized in polar solvents than the less polar ground state, fluo-
rescence undergoes bathochromic shift depending on the solvent
polarities. Hirata already reported that aminoacetylenes
H2NeC6H4eC^CeC6H5 and H2NeC6H4eC^CeC6H4CN emit
veloped, the structures of which are depicted as donor-(p-system)/
acceptor.11 These dyes are designed for the electron density of
HOMO to be wholly located on the donor group and for LUMO
electron density to be on the acceptor, and, upon photo-excitation,
* Corresponding authors. Tel.: þ81 86 256 9533; fax: þ81 86 256 4292 (A.O.); tel./
fax: þ86 731 8827 944 (D.-L.A.); e-mail addresses: deliean@sina.com (D.-L. An),
orita@high.ous.ac.jp (A. Orita).
an intramolecular electron transfer occurs through the
p-system
bridge to attain a discrete charge-transferred excited state. Because
0040-4020/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tet.2010.05.016

5480
J.-K. Fang et al. / Tetrahedron 66 (2010) 5479e5485
charge-transferred excited state. Herein we report syntheses of
Ph2N
Ph2N
X
several phenylenee(poly)ethynylenes, which have Ph2N or Ph2N/
CN groups at their terminal(s) and their photophysical properties
such as UV/vis absorption, photoluminescence, and change of
dipole moments Dm between excited and ground states, which are
estimated by Lippert/Mataga plot.12
X = H (1), CN (4)
Et
Et
Et
X
Et
Et
Et
Et
X = H (2), CN (5)
Et
Et
2. Results and discussion
Ph2N
X
Et
We firstly prepared Ph2N or Ph2N/cyano-substituted phenyl-
eneethynylenes 1e14 (Fig. 1). Syntheses of 1e6 were attained by
repeating Sonogashira coupling between the corresponding ter-
minal acetylene and halobenzene. Representative synthetic process
for 5 is shown in Scheme 1, and 5 was obtained as yellow powdery
compound, and 13C NMR analysis featured six acetylenic carbons
X = H (3), CN (6)
Ph2N
Ph2N
n
n = 2 (7), 3 (8)
(d 87.4, 92.3, 92.4, 92.8, 93.6, 94.7), and cyano carbon (d 118.5). All
the acetylenes 1e6 are white to yellow powdery compounds, which
are stable in air. Substitution of ethyl groups on central benzenes of
the higher homologs improved their poor solubilities to enable
5 and 6 to be miscible with common organic solvents.
n
n = 2 (9), 3 (10)
Ph2N
Ph2N
CN
CN
For synthesis of Ph2N-7e10 and Ph2N/cyano-substituted
phenylenee(poly)ethynylenes 11e14, we established a general
procedure: diphenylethyne and polyethyne moieties were con-
structed by Sonogashira coupling and double elimination protocol,
respectively. Representative synthetic processes for 14 and 12 are
shown in Scheme 2. Cyano-substituted propargyl sulfone 17 was
obtained by m-CPBA-oxidation of the corresponding propargyl
sulfide 18, that had been prepared by Sonogashira coupling of
4-bromobenzonitrile with propargyl sulfide. Amino-substituted
propargylaldehyde 19 was obtained by MnO2-oxidation of prop-
argyl alcohol 20, that had been prepared by stepwise Sonogashira
coupling of 1-bromo-4-iodobenzene 21 with aminophenylethyne
22 and propynol 23. Although Sonogashira coupling using
n
n = 2 (11), 3 (12)
n
n = 2 (13), 3 (14)
Figure 1. Structures of 1e14.
this charge-transfer excitation of the organic dye plays a pivotal
role to achieve high solar-to-electric power conversion, we have
been intrigued by the effect of acetylenic
p-system and electron-
accepting group on nature of donor-(
p
-system)/acceptor dye in the
TMS
Pd(PPh3)4, CuI
K2CO3
TMS
Ph2N
I
Ph2N
Toluene, i-Pr2NH
80 °C, overnight
THF, CH3OH
95%
rt, 2 h
Et
I
I
TMS
Et
Et
Pd(PPh3)4, CuI
Pd(PPh3)4, CuI
Ph2N
I
Ph2N
Ph2N
Toluene, i-Pr2NH
Toluene, i-Pr2NH
rt, overnight
rt, overnight
Et
96%
64%
Et
Et
K2CO3
Ph2N
TMS
THF, CH3OH
rt, 2 h
Et
15 98%
Et
98%
CN
TMS
Pd(PPh3)4, CuI
K2CO3
CN
Br
TMS
CN
Toluene, i-Pr2NH
rt, overnight
THF, CH3OH
rt, 2 h
quant.
CN
81%
Et
I
I
TMS
Et
Et
Pd(PPh3)4, CuI
Pd(PPh3)4, CuI
I
Toluene, i-Pr2NH
rt, overnight
Toluene, i-Pr2NH
rt, overnight
Et
16 59%
Et
Et
Pd(PPh3)4, CuI
Ph2N
CN
15
+
16
Toluene, i-Pr2NH
rt, overnight
Et
Et
5 97%
Scheme 1. Synthesis of 5.

J.-K. Fang et al. / Tetrahedron 66 (2010) 5479e5485
5481
m-CPBA
CN
CN
CH2Cl2/CH3OH
0 °C, 2 h
PhS
PhSO2
18
17
Ph2N
OH
23
22
Pd(PPh3)4, CuI
Pd(PPh3)4, CuI
I
Br
Ph2N
Br
toluene, i-Pr2NH
60 °C, overnight
toluene, i-Pr2NH
rt, overnight
93 %
Ph2N
21
MnO2
CHO
19 81 %
Ph2N
CH2Cl2,
OH
35 °C,
20 83 %
overnight
ClP(O)(OEt)2
LiHMDS
19 + 17
Ph2N
CN
THF,
-78 °C- 0 °C, 3 h
14 15%
ClP(O)(OEt)2
LiHMDS
+
OHC
CN
Ph2N
THF,
SO2Ph
-78 °C- 0 °C, 3 h
Ph2N
CN
12 19%
Scheme 2. Syntheses of 14 and 12.
a propargylaldehyde derivative is indeed straightforward for syn-
thesis of 19, this coupling reaction afforded an inseparable mixture
of a number of products (Eq. 1). Subjection of the propargyl sulfone
17 and aldehyde 19 to one-shot double elimination reaction gave
the desired product 14: when a THF solution of LiHMDS (lithium
hexamethyldisilazide) was added to a THF solution of 17, 19, and
diethyl chlorophosphate, 14 was obtained in 15% yield in a pure
form after column chromatography on silica gel. TLC analysis of
crude products of this double elimination indicated remarkable
formation of unidentified polar compounds resulting in the low
yield of the desired product. Ph2N/cyano-acetylene 14 thus
obtained is yellow powdery compound, which is stable at room
temperature in air but decomposed over 200 ꢀC. When 13C NMR of
Ph2N
Ph2N
+
OH
X
CN
CHO
+
PhSO2
route 1
24
ClP(O)(OEt)2
LiHMDS
Ph2N
CN
14
ClP(O)(OEt)2
LiHMDS
route 2
OHC
14 was recorded in CDCl3, eight acetylenic carbons (
d
66.4, 68.6,
75.6, 76.6, 78.4, 79.6, 88.1, 93.4) and cyano carbon (
d
118.1) were
Ph2N
+
CN
CN
observed. Hexatriyne derivative 12 was successfully synthesized as
well by taking advantage of the double elimination as a key re-
action (Scheme 2). Although, in these syntheses, propargyl sulfone
and propargylaldehyde were used for construction of the hexa-
triyne motif, double elimination reaction between benzyl sulfone
and penta-1,3-diynal were supposed to be an alternative synthetic
route (Scheme 3). We attempted to prepare penta-1,3-diynals 24
and 25 by Cu(OAc)2-catalyzed oxidative coupling between terminal
acetylenes followed by MnO2 oxidation, but complicated mixtures
of products were obtained in both cases.
SO2Ph
25
X
+
HO
Scheme 3. Attempted synthetic route for 14.
Sonogashira coupling with 28 furnished 11. For synthesis of 13,
vinylsulfone 29 was exploited as a masked diyne 30 because its
polarity enabled a facile purification of Sonogashira coupling
product 31. The vinylsulfone 29 could be obtained by treatment of
the corresponding aldehyde, sulfone, and diethyl chlorophosphate
with 2 equiv of LiHMDS. When 31 was treated with t-BuOK in THF,
elimination of sulfinic acid proceeded smoothly to give 13 in 78%
yield.
ð1Þ
Combination of Sonogashira coupling and double elimination
protocol were applied for syntheses of diphenylbutadiyne deri-
varives 11 and 13 (Scheme 4). Subjection of propargylaldehyde 26
and benzyl sulfone 27 to double elimination followed by

5482
J.-K. Fang et al. / Tetrahedron 66 (2010) 5479e5485
ClP(O)(OEt)2
LiHMDS
I
Ph2N
CHO
+
PhSO2
THF, -78 °C - 0 °C,
overnight
26
27
CN
28
Pd(PPh3)4, CuI
11 94 %
Ph2N
I
toluene, i-Pr2NH
rt, overnight
75 %
ClP(O)(OEt)2
LiHMDS (2 equiv)
I
I
CHO
+
CN
CN
THF,
PhSO2
PhSO2
29 52 %
-78 °C - 0 °C, 3 h
I
CN
30
Ph2N
22
Pd(PPh3)4, CuI
t-BuOK
THF,
Ph2N
13
toluene, i-Pr2NH
rt, overnight
CN
78 %
0 °C - rt, 3 h
PhSO2
31 97 %
Scheme 4. Syntheses of 11 and 13.
Photophysical properties of the Ph2N- and Ph2N/cyano-
substituted acetylenes 1e14 were summarized in Table 1. All the
spectral data were recorded in CH2Cl2, and absolute quantum yields
expanded p-systems exhibit smaller bathochromic shifts: 1/4
(
Dlabs¼8 nm), 3/6 (1 nm); 7/11 (4 nm), 8/12 (2 nm); 9/13
(7 nm), 10/14 (ca. 0 nm).13 Seven figures of UV/vis absorption
spectra of 1 and 4, 2 and 5, 3 and 6, 7 and 11, 8 and 12, 9 and 13, 10
and 14 are added in Supplementary data in order to make clear an
electronic effect of cyano group on wavelengths of labs. Expansion
(FF) were determined by the Hamamatsu C9920e02 integrated
sphere system. Fluorescence decays were measured using an
apparatus including a femtosecond laser system and a streak
camera.
of
p-system by insertion of a phenyleneethynylene unit
Several consistent trends are seen in UV/vis absorption spectra
of 1e14. Substitution of Ph2Nephenylenee(poly)ethynylene with
cyano group induces bathochromic shift of labs by several nano-
meters compared to the parent Ph2N-acetylenes, and largely
(eC6H4C^Ce) results in a bathochromic shift, while insertion of
an ethynylene unit (eC^Ce) caused larger shifts: for phenyl-
eneethynylene insertion,
1
(labs 373 nm)/2 (374 nm)/3
(382 nm); for ethynylene insertion, 1 (labs 373 nm)/9 (385 nm)/
Table 1
Photophysical properties of Ph2N- and Ph2N/CN-substituted phenylenee(poly)ethynylenes 1e14 in CH2Cl2
3a [L/mol cm]
D
E
b [eV]
lemc [nm]
Stokes shift [cmꢁ1
]
FF
se [ns]
kr, knr [108/s]
kr/knr
r
[102]
a
d
f
labs [nm]
1
2
3
4
5
6
7
8
373
374
382
381
380
383
392
392
385
401
396
394
392
399
4.6ꢂ104
6.7ꢂ104
8.5ꢂ104
4.7ꢂ104
7.2ꢂ104
9.9ꢂ104
5.2ꢂ104
4.5ꢂ104
5.3ꢂ104
6.1ꢂ104
5.0ꢂ104
4.1ꢂ104
4.8ꢂ104
5.1ꢂ104
3.26
3.02
2.88
2.89
2.71
2.62
3.11
2.95
3.07
2.88
2.79
2.70
2.72
2.55
467
470
472
514
501
477
478
496
491
523
514
522
539
554
5396
5461
4992
6791
6356
5145
4590
5349
5607
5817
5797
4224
6957
7012
0.89
0.91
0.91
0.84
0.67
0.62
0.40
0.01
0.86
0.68
0.45
0.02
0.65
0.22
1.6
1.2
1.4
2.2
2.0
1.8
0.7
5.6, 0.69
7.6, 0.75
6.5, 0.64
3.8, 0.73
3.4, 1.7
3.4, 2.1
5.7, 8.6
8.1
10.1
10.1
5.2
2.0
1.6
145
138
136
177
173
106
147
135
154
167
177
134
170
143
0.66
9
1.7
1.7
1.5
5.1, 0.82
4.0, 1.9
3.0, 3.7
6.2
2.1
0.82
10
11
12
13
14
2.7
1.2
2.4, 1.3
1.8, 6.5
1.9
0.28
a
UV/vis absorption in CH2Cl2 (1.0ꢂ10ꢁ5 M).
b
c
d
e
f
Energy difference between HOMO and LUMO calculated at the B3LYP/6-31G level.
*
Fluorescence maximum in CH2Cl2 (1.0ꢂ10ꢁ7 M).
Fluorescence quantum yield measured by integrated sphere system (Hamamatsu photonics C9920e02).
Fluorescence lifetime, solutions degassed by freeze-pump-thraw cycles, 5.0ꢂ10ꢁ6 M.
kr¼FF/s, knr¼(1ꢁFF)/s.

J.-K. Fang et al. / Tetrahedron 66 (2010) 5479e5485
5483
Figure 2. Molecular orbitals of 10 and 14 calculated by DFT method.
10 (401 nm). The degree of bathochromic shift shows fine agree-
ment to E values, which are HOMO/LUMO gaps calculated at the
B3LYP/6-31G
level.14 In Figure 2 are shown molecular orbitals of 10
and 14, which have been calculated by the DFT method. The
HOMOs are located mainly on the electron-donating triphenyl-
amine moieties with a small participation of phenylenee(poly)
ethynylene moieties, while the LUMOs mainly on phenylenee
insertion,
C6H4C^C insertion, 1 (lem 467 nm)/2 (470 nm)/3 (472 nm).
Interestingly, in Ph2N/cyano-phenyleneethynylene series 4e6,
system expansion by insertion of C6H4C^C leads a blue-shift; the
homolog with the shortest -system 4 emits fluorescence at the
longest wavelength among this series. This result can be explained
in terms of intramolecular donor/acceptor interaction in the excited
state, which is enhanced by proximately locating Ph2N and CN
groups resulting in a narrow S1eS0 gap.10b All the acetylenes 1e14
exhibit considerably large Stokes shift (>4200 cmꢁ1), and Stokes
shifts of Ph2N/cyano derivatives generally exceed those of the
corresponding Ph2N derivatives. Comparison of fluorescence
quantum yields FF displays that the quantum yields of diynes and
1 (lem 467 nm)/9 (491 nm)/10 (523 nm); for
D
*
p-
p
(poly)ethynylene moieties with
a great participation of the
accepting cyano group in 14. Such remarkable localization of HOMO
and LUMO in different areas strongly suggests an intramolecular
charge-transfer excitation to occur in 1e14 resulting in polarization
of excited state S1. In cyano-substituted compounds, a further po-
larization is expected because of the strong electron-withdrawing
feature of cyano group as shown in Figure 2. In order to elucidate
polarization of 1e14 in S1 states, photoluminescence spectra were
recorded in several polarity-varying solvents. Emission profiles of
14 in five different solvents are shown in Figure 3 together with UV/
vis absorption spectra.15 Obviously, the emission maxima lem of 14
are shifted to longer wavelengths as solvent polarity increases,16
while the absorption maxima labs displays virtually no change in
any solvents. These results unambiguously support that highly
polarized excited state of 14 is stabilized depending on the solvent
polarity, while 14 in the ground state undergoes little solvent
polarity effect because of its less dipole moment (vide infra). In
Table 1 are summarized photoluminescence properties of 1e14
such as emission maximum lem, Stokes shift, and fluorescence
quantum yield observed in CH2Cl2. The emission maxima lem show
the similar trends as observed in absorption maxima labs of UV/vis
absorption spectra: substitution by cyano group provides a bath-
ochromic shift, and insertion of eC^Ce unit more efficiently ex-
triynes remarkably decrease as the polyyne
p-system e(C^C)ne
expands; 4 (FF 0.84)/13 (0.65)/14 (0.22). In order to get further
insight into a mechanism for low emission quantum yields of diyne
and triyne derivatives, fluorescence lifetimes
1e14. Reaction rates for radiative kr and nonradiative processes knr
are obtained by the following equations (kr¼FF , knr¼(1ꢁFF)/ ),
and the rate constants kr, knr, and the constant ratio kr/knr are
summarized in Table 1. Notably, as polyyne -system expands,
s were recorded for
/s
s
p
nonradiative reaction rate constant knr drastically increases and
consequently a ratio of reaction rate constants kr/knr decreases
resulting in low fluorescence quantum yields of diynes and triynes:
4 (knr¼0.73, kr/knr¼5.2)/13 (1.3, 1.9)/14 (6.5, 0.28); 1 (knr¼0.69,
kr/knr¼8.1)/9 (0.82, 6.2)/10 (1.9, 2.1). The solvent polarity effect
on lem and large Stokes shifts observed in 1e14 suggest increase of
their dipole moments in the excited states S1 (me) compared to
those in the ground state S0 (mg). In order to rationalize the effect of
solvent polarity on the dipole moment change Dm, which corre-
pands acetylenic
p
-system than eC6H4C^Ce unit: for C^C
sponds to me
ꢁ
mg, we took advantage of the Lippert/Mataga plot,12
which provides quantitative relationship between the solvent ori-
entation polarizability
and 3:
Df and Stokes shift
D
v by the following Eqs. 2
ꢀ
ꢁ
2
me
ꢁ
mg
2
hc
(2)
D
V ¼
D
f þ Constant
a3
¼
rDf þ C
3
ꢁ 1
n2 ꢁ 1
D
f ¼
ꢁ
(3)
2n2 þ 1
2
3
þ 1
where
Dv denotes Stokes shift, me the excited state dipole mo-
ment, mg the ground state dipole moment, h the Planck constant, c
the light velocity, and a the Onsager radius of the solute. The sol-
vent orientation polarizability
dielectric constant and refractive index n, is calculated by using
Eq. 3.17 Plotting of f affords 2(Dm)2/hca3 as the slope
v versus of
linear fit, and in Table 1 are represented the slope values thus
Df, which is related to the solvent
3
D
D
r
Figure 3. Normalized UV/vis absorption and emission spectra of 14 in cyclohexane
2.0), toluene ( 2.4), CHCl3 4.8), THF ( 7.6), and CH2Cl2 8.9).
r
(
3
3
(
3
3
(3

5484
J.-K. Fang et al. / Tetrahedron 66 (2010) 5479e5485
obtained for 1e14.13 All the acetylenes exhibit remarkably large
slope values (>10,000) indicating charge-transfer excitation oc-
curs with large change of dipole moments Dm 10
Provided that
Onsagar radii of 4e6 are identical to those of the corresponding
analogs 1e3, respectively, by disregarding bulkiness of cyano
added at 0 ꢀC, and the mixture was stirred at room temperature
overnight. After usual workup with CH2Cl2/NH4Claq, the combined
organic layer was dried over MgSO4, and evaporated. The crude
product was subjected to column chromatography on silica gel
(hexane/CH2Cl2, 4:1) to give 556 mg of 4-iodo-40-(dipheynylamino)
diphenylbutadiyne (75% yield) as a pale yellow powder.
r
.
group, comparison of
of cyano group on Dm(¼me
acetylenes 4 (17,700) and 5 (17,300) represents large
r
values enables to estimate electronic effect
mg) of these acetylenes. Ph2N/cyano
values
ꢁ
4-Iodo-40-(dipheynylamino)diphenylbutadiyne: Mp 163e165 ꢀC;
r
1H NMR (500 MHz, CDCl3)
d
6.95 (d, 8.5 Hz, 2H), 7.08 (t, 7.5 Hz, 2H),
7.11 (d, 8.0 Hz, 4H), 7.21 (d, 8.0 Hz, 2H), 7.28 (t, 8.0 Hz, 4H), 7.34 (d,
8.5 Hz, 2H), 7.66 (d, 8.0 Hz, 2H); 13C NMR (125 MHz, CDCl3)
72.88,
compared to those of the corresponding Ph2N acetylenes 1 (14,500)
and 2 (13,800) indicating that the changes of dipole moments Dm
are magnified by substitution with electron-withdrawing cyano
d
75.75, 80.22, 83.06, 95.15, 113.33, 121.25, 121.53, 124.04, 125.39,
129.48, 133.51, 133.70, 137.57, 146.71, 148.83.
group. For Ph2N/cyano higher homolog 6, the
be 10,600, which is smaller than that of 3 (13,600), representing
that substitution of highly conjugated -system with cyano group
results in a smaller change of dipole moment Dm than that of the
parent Ph2N -system. Because the Onsager radii a can be con-
r value is provided to
To a flask were added 28 (19 mg, 0.15 mmol), 4-iodo-40-
(dipheynylamino)diphenylbutadiyne (82 mg, 0.17 mmol), Pd
(PPh3)4 (11 mg, 0.01 mmol), CuI (2 mg, 0.01 mmol), diisopropyl-
amine (5 mL), and toluene (5 mL), and the mixture was stirred
under nitrogen at room temperature overnight. After usual workup
with CH2Cl2/NH4Claq, the combined organic layer was dried over
MgSO4 and evaporated. The crude product was subjected to column
chromatography on silica gel (hexane/CH2Cl2, 1:1) to give 70 mg of
11 (94% yield) as a pale yellow powder.
p
p
sidered to be identical in regioisomeric pairs, Ph2N-butadiynes 7, 9,
and Ph2N/cyano-butadiynes 11, 13, respectively, comparison of
their
r values enables to evaluate explicitly effects of regioisomeric
acetylene mode and cyano group on the change of dipole moments
Dm. Both pairs of Ph2N-butadiynes 7, 9, and Ph2N/cyano-butadiynes
11, 13 represent comparable
effect of location of butadiyne moiety on change of dipole moments
Dm. It is notable that the value of Ph2N-hexatriyne 10 is signifi-
cantly larger than that of the regioisomer 8, and the remarkably
large value of 10 is in good agreement with our previous report
r
values, respectively, indicating no
Compound 11: Mp 248e250 ꢀC; 1H NMR (500 MHz, CDCl3)
d 6.96
(d, 9.0 Hz, 2H), 7.10 (t, 7.5 Hz, 2H), 7.12 (d, 7.5 Hz, 4H), 7.29 (t, 8.0 Hz,
r
4H),7.36(d, 9.0 Hz, 2H), 7.48e7.52(m, 4H),7.60(d, 8.5 Hz,2H), 7.65(d,
8.5 Hz, 2H); 13C NMR (125 MHz, CDCl3)
d 72.88, 76.72, 80.56, 83.68,
r
90.00, 93.16, 111.69, 113.25, 118.46, 121.21, 122.58, 122.79, 124.08,
125.42, 127.80, 129.49, 131.71, 132.08, 132.37, 133.54, 146.70, 148.90;
HRMS m/z [M]þ calcd for C37H22N2 494.1783, found 494.1793.
describing that hexatriyne moiety captures a negative charge in the
excited state providing high polarization.9 Ph2N/cyano-hexatriynes
12 and 14 show similar
r values, indicating no effect of regiomeric
acetylene modes on change of dipole moments Dm in them. The
r
4.2. Synthesis of 12
value of 14 is rather smaller than that of 10 suggesting, under as-
sumption of the identical Onsager radius a in 14 and 10, a smaller
change of dipole moment Dm in 14 despite the substitution of
hexatriyne moiety by electron-withdrawing cyano group.18 These
results exemplify that substitution by electron-withdrawing cyano
group does not always promote larger change of dipole moments in
the charge-transfer excitation as observed in highly conjugated
To a flask were added 4-(4-cyanophenylethynyl)phenylpropynal
(128 mg, 0.50 mmol), phenyl 1-(4-diphenylaminophenyl)propyn-
3-yl sulfone (254 mg, 0.60 mmol), diethyl chlorophosphate
(172 mg, 0.50 mmol), and THF (10 mL) under nitrogen. A THF so-
lution of LiHMDS (1.5 mL, 1.0 M, 1.5 mmol) was added at ꢁ78 ꢀC,
and the mixture was stirred at 0 ꢀC for 3 h. After usual workup with
CH2Cl2/NH4Claq, the combined organic layer was dried over MgSO4
and evaporated. The crude product was subjected to column
chromatography on silica gel (hexane/CH2Cl2, 1:1) to give 50 mg of
12 (19% yield) as a yellow powder.
acetylene
p-systems such as 14 and 6, and the origin of this in-
triguing effect of cyano group on change of dipole moment remains
to be investigated.
3. Conclusion
Compound 12: Mp>250 ꢀC decomp.; 1H NMR (500 MHz, CDCl3)
d
6.93 (d, 9.0 Hz, 2H), 7.11 (t, 8.0 Hz, 2H), 7.12 (d, 8.5 Hz, 4H), 7.30 (t,
In conclusion, we established a synthetic process for Ph2N or
8.0 Hz, 4H), 7.36 (d, 9.0 Hz, 2H), 7.49 (d, 8.5 Hz, 2H), 7.52 (d, 8.5 Hz,
Ph2N/cyano-substituted acetylenic
p
-systems by invoking Sono-
-substituted sulfone
2H), 7.60 (d, 8.5 Hz, 2H), 7.65 (d, 8.5 Hz, 2H); 13C NMR (125 MHz,
gashira coupling and double elimination of
b
CDCl3) d 66.06, 68.38, 73.71, 76.85, 77.73, 80.34, 90.41, 93.03, 111.88,
for construction of diphenylethyne and diphenylpolyethyne
moieties, respectively. Thorough investigation of photophysical
properties of these acetylenes disclosed that they underwent
charge-separated excitation to emit fluorescence with significant
112.24, 118.41, 120.96, 121.96, 123.24, 124.32, 125.62, 127.75, 129.56,
131.77, 132.10, 132.13, 132.91, 134.11, 146.61, 149.35; HRMS m/z [M]þ
calcd for C39H22N2 518.1783, found 518.1788.
bathochromic shifts. Substitution of acetylenic
p
-systems with
4.3. Synthesis of 13
cyano group provided large changes of dipole moments upon their
excitation resulting in the large bathochromic shift of emission
although substitution of highly expanded acetylenic p-systems did
small changes. Further investigation of the mechanism and appli-
cation of these results for design of organic photosensitizer are in
progress in our laboratories.19
To a round-bottom flask were added 4-cyanophenylmethyl
phenyl sulfone (154 mg, 0.6 mmol), 4-iodopheynylpropynal
(128 mg, 0.5 mmol), diethyl chlorophosphate (86 mg, 0.5 mmol),
and THF (20 mL) under nitrogen. A THF solution of LiHMDS (1.0 mL,
1.0 M, 1.0 mmol) was added at ꢁ78 ꢀC, and the mixture was stirred
at room temperature for 3 h. After usual workup with CH2Cl2/
NH4Claq, the combined organic layer was dried over MgSO4 and
evaporated. The crude product was subjected to column chroma-
tography on silica gel (hexane/EtOAc, 4:1) to give 128 mg of 29 (52%
yield) as a pale yellow foam. The product 29 was obtained as a pure
geometric isomer, but the geometry E or Z was not determined.
4. Experimental
4.1. Synthesis of 11
To a round-bottom flask were added 4-iodophenylmethyl phe-
nyl sulfone (645 mg, 1.8 mmol), 26 (446 mg, 1.5 mmol), diethyl
chlorophosphate (259 mg, 1.5 mmol), and THF (20 mL) under ni-
trogen. A THF solution of LiHMDS (7.5 mL, 1.0 M, 7.5 mmol) was
Compound 29: Mp 136e138 ꢀC; 1H NMR (500 MHz, CDCl3)
d 6.92
(d, 8.0 Hz, 2H), 7.32 (s, 1H), 7.45 (t, 7.5 Hz, 2H), 7.50 (d, 8.0 Hz, 2H),
7.58 (t, 7.0 Hz, 1H), 7.63e7.66 (m, 6H); 13C NMR (125 MHz, CDCl3)

J.-K. Fang et al. / Tetrahedron 66 (2010) 5479e5485
5485
d
84.79, 96.57, 102.16, 113.25, 118.11, 120.52, 121.09, 128.23, 129.16,
References and notes
130.78, 131.81, 133.18, 133.89, 135.37, 137.71, 137.97, 149.03.
To a flask were added 4-ethynyl-N,N-diphenylbenzenamine
(43 mg, 0.16 mmol), 29 (84 mg, 0.17 mmol), Pd(PPh3)4 (11 mg,
0.01 mmol), CuI (2 mg, 0.01 mmol), diisopropylamine (5 mL), and
toluene (5 mL), and the mixture was stirred under nitrogen at room
temperature overnight. After usual workup with CH2Cl2/NH4Claq, the
combined organic layer was dried over MgSO4 and evaporated. The
crude product was subjected to column chromatography on silica gel
(hexane/EtOAc, 4:1)to give 99 mgof 31 (97%yield) asan orange foam.
1. (a) Acetylene Chemistry: Chemistry, Biology, and Material Science; Diederich, F.,
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4. (a) Doi, T.; Orita, A.; Matsuo, D.; Saijo, R.; Otera, J. Synlett 2008, 55; (b) Orita, A.;
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Yokoyama, T.; Babu, G.; Otera, J. Chem. Lett. 2004, 33, 1298; (d) Orita, A.;
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Adachi, C.; Otera, J. Mater. Chem. Phys. 2009, 115, 378; (c) Ding, C.; Babu, G.;
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Mineyama, H.; Otera, J. Synlett 2007, 1909; (e) Fenenko, L.; Shao, G.; Orita, A.;
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Compound 31: Mp 91e93 ꢀC; 1H NMR (500 MHz, CDCl3)
d 6.99
(d, 8.0 Hz, 2H), 7.07 (t, 7.0 Hz, 2H), 7.11 (d, 7.5 Hz, 4H), 7.16 (d, 7.5 Hz,
2H), 7.27 (d, 7.5 Hz, 4H), 7.34 (d, 8.5 Hz, 2H), 7.36 (s, 1H), 7.40 (d,
8.0 Hz, 2H), 7.45 (t, 7.5 Hz, 2H), 7.52 (d, 7.5 Hz, 2H), 7.58 (t, 7.0 Hz,
1H), 7.65 (t, 7.0 Hz, 4H); 13C NMR (125 MHz, CDCl3)
d 85.21, 87.97,
93.11, 103.20, 113.25, 114.99, 118.22, 120.22, 121.36, 121.83, 123.71,
125.08, 125.49, 128.26, 129.19, 129.39, 130.89, 131.38, 131.86, 131.92,
132.58, 133.88, 135.51, 138.17, 146.92, 148.28, 148.61.
To a round-bottom flask were added 31 (83 mg, 0.13 mmol),
potassium tert-butoxide (16 mg, 0.14 mmol), and THF (5 mL) under
nitrogen at 0 ꢀC. The mixture was stirred at room temperature for
3 h. After usual workup with CH2Cl2/NH4Claq, the combined organic
layer was dried over MgSO4 and evaporated. The crude product was
subjected to column chromatography on silica gel (hexane/CH2Cl2,
1:1) to give 50 mg of 13 (78% yield) as a yellow powder.
Compound 13: Mp 245e247 ꢀC; 1H NMR (500 MHz, CDCl3)
d 7.01
(d, 8.5 Hz, 2H), 7.08 (t, 7.5 Hz, 2H), 7.12 (d, 8.0 Hz, 4H), 7.28 (t, 8.0 Hz,
4H), 7.36 (d, 9.0 Hz, 2H), 7.47 (d, 8.5 Hz, 2H), 7.50 (d, 8.5 Hz, 2H),
7.60 (d, 8.5 Hz, 2H), 7.63 (d, 8.5 Hz, 2H); 13C NMR (125 MHz, CDCl3)
6. Molecular Fluorescence: Principles and Applications; Valeur, B., Ed.; VCH: Wein-
heim, Germany, 2001, Chapter 3.
7. Hirata, Y.; Okada, T.; Nomoto, T. J. Phys. Chem. A 1998, 102, 6585.
8. Hirata, Y.; Okada, T.; Nomoto, T. Chem. Phys. Lett. 1997, 278, 133.
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Matsuo, D.; Orita, A.; Otera, J. Tetrahedron Lett. 2010, 51, 917.
d
74.77, 78.05, 80.12, 83.64, 88.08, 93.00, 112.35, 115.17, 118.24,
120.23, 121.92, 123.71, 125.10, 126.69, 129.41, 131.41, 132.09, 132.48,
132.60, 132.89, 146.99, 148.28; HRMS m/z [M]þ calcd for C37H22N2
494.1783, found 494.1779.
10. (a) Shimoi, Y.; Yamaguchi, Y.; Yoshida, Z.-I. Synth. Metal 2009, 159, 2211; (b)
Yamaguchi, Y.; Shimoi, Y.; Ochi, T.; Wakamiya, T.; Matsubara, Y.; Yoshida, Z.-I. J.
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Yamaguchi, Y.; Kobayashi, S.; Wakamiya, T.; Matsubara, Y.; Yoshida, Z.-I. Chem.
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4.4. Synthesis of 14
To a flask were added 19 (100 mg, 0.25 mmol), 17 (85 mg,
0.30 mmol), diethyl chlorophosphate (86 mg, 0.25 mmol), and THF
(10 mL) under nitrogen. A THF solution of LiHMDS (0.75 mL, 1.0 M,
0.75 mmol) was added at ꢁ78 ꢀC, and the mixture was stirred at 0 ꢀC
for 3 h. After the usual workup with CH2Cl2/NH4Claq, the combined
organic layer was dried over MgSO4 and evaporated. The crude
product was subjected to column chromatography on silica gel
(hexane/CH2Cl2, 1:1) to give 20 mg of 14 (15% yield) as a pale yellow
powder.
€
11. For recent reviews on molecular photovoltaics: (a) Gratzel, M. Acc. Chem. Res.
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M. Coord. Chem. Rev. 1998, 171, 245 For recent reviews on organic dye for solar
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13. See Supplementary data for details.
Compound 14: Mp>250 ꢀC decomp.; 1H NMR (500 MHz, CDCl3)
14. Theoretical calculations were carried out on 1e14 with benzene rings of phe-
nylenee(poly)ethynylenes fixed in the same plane by using Spartan ’08
(Wavefunction, Inc.). Schematic HOMOs and LUMOs of 1e14 were shown in
Supplementary data together with their energy levels.
15. When emission spectra of Ph2N/cyano-substituted acetylene 14 were recorded,
some decomposition was observed in polar solvents such as DMF and MeCN.
16. This bathochromic shift can be attributed not to excimer formation but to
solvent polarity effect because emission spectra of 2 were identical in 10ꢁ4 M to
10ꢁ7 M of CH2Cl2 solution indicating no sign of excimer formation. See
Supplementary data.
d
7.00 (d, 8.5 Hz, 2H), 7.08 (t, 7.5 Hz, 2H), 7.12 (d, 8.0 Hz, 4H), 7.29 (t,
7.5 Hz, 4H), 7.36 (d, 8.5 Hz, 2H), 7.46 (d, 8.0 Hz, 2H), 7.50 (d, 8.0 Hz,
2H), 7.61 (d, 8.0 Hz, 2H), 7.64 (d, 8.0 Hz, 2H); 13C NMR (125 MHz,
CDCl3) d 66.37, 68.61, 75.60, 76.60, 78.40, 79.62, 88.08, 93.39, 112.81,
115.11, 118.11, 119.59, 121.90, 123.75, 125.14, 125.49, 125.98, 129.43,
131.43, 132.12, 132.62, 132.94, 133.35, 147.00, 148.34; HRMS m/z
[M]þ calcd for C39H22N2 518.1783, found 518.1791.
17. Solvent dielectric constants
3 and refractive indices n were taken from the
following: Montalti, M.; Credi, A.; Prodi, L.; Gandolfi, M. T. Handbook of Photo-
chemistry, 3rd ed.; Taylor & Francis: New York, NY, 2006.
Acknowledgements
18. This smaller change of dipole moments Dm could be explained in terms of
larger polarization of 14 in the ground state than in the excited state attributed
to electron-withdrawing effect of cyano group, but this explanation is un-
ambiguously excluded because of little solvent effect observed in UV/vis
absorption spectra.
19. Herein we would like to limit description of syntheses of phenylene(poly)
ethynylenes 1e14 and their UV/vis absorption and photoluminescence
spectral data together with discussion of change of dipole moments Dm
between their excited and ground states because the main issue of this
paper is evaluation of electronic effect of acetylenic modes on charge-
This work was supported by the Grant-in-Aid for Scientific Re-
search and matching fund subsidy for private universities from
MEXT (Ministry of Education, Culture, Sports, Science and Tech-
nology), Japan, and Okayama Prefecture Industrial Promotion
Foundation.
Supplementary data
transferred excited states in donor-p-system/acceptor dyes. As one of re-
Experimental procedure, characterization details are fully
provided. Supplementary data associated with this article can be
found, in the online version, at doi:10.1016/j.tet.2010.05.016.
viewers suggested, we are planning to investigate other optoelectronic
properties such as two photon absorption and two photon fluorescence of
1e14 in the near future.