Synthesis and spectroscopic study of diphenylamino-substituted phenylene-(poly)ethynylenes: remarkable effect of acetylenic conjugation modes

Article abstract of DOI:10.1016/j.tetlet.2009.12.023

A series of diphenylamino-substituted phenylene-(poly)ethynylenes were successfully synthesized by a combination of Sonogashira coupling and double elimination protocol of β-substituted sulfones. When UV-light was irradiated, the amino-substituted phenylene-(poly)ethynylene emitted strong luminescence. The emission underwent a large bathochromic shift in polar solvent because of stabilization of their charge-separated excited states. Analyses of fluorescence life times of aminoacetylenes revealed that radiationless process was suppressed in the polar solvent CH₂Cl₂, resulting in high quantum yields.

Full text of DOI:10.1016/j.tetlet.2009.12.023

Tetrahedron Letters 51 (2010) 917–920
Contents lists available at ScienceDirect
Tetrahedron Letters
journal homepage: www.elsevier.com/locate/tetlet
Synthesis and spectroscopic study of diphenylamino-substituted
phenylene-(poly)ethynylenes: remarkable effect of acetylenic conjugation
modes
b
b
b
b
Jing-Kun Fang a,c, De-Lie An a, , Kan Wakamatsu , Takeharu Ishikawa , Tetsuo Iwanaga , Shinji Toyota ,
*
c,*
Daisuke Matsuo c, Akihiro Orita c, , Junzo Otera
*
a Department of Chemistry, College of Chemistry and Chemical Engineering, Hunan University, Changsha 410082, China
b Department of Chemistry, Okayama University of Science, Ridai-cho, Okayama 700-0005, Japan
c Department of Applied Chemistry, Okayama University of Science, Ridai-cho, 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:
A series of diphenylamino-substituted phenylene-(poly)ethynylenes were successfully synthesized by a
combination of Sonogashira coupling and double elimination protocol of b-substituted sulfones. When
UV-light was irradiated, the amino-substituted phenylene-(poly)ethynylene emitted strong lumines-
cence. The emission underwent a large bathochromic shift in polar solvent because of stabilization of
their charge-separated excited states. Analyses of fluorescence life times of aminoacetylenes revealed
that radiationless process was suppressed in the polar solvent CH2Cl2, resulting in high quantum yields.
Ó 2009 Elsevier Ltd. All rights reserved.
Received 30 November 2009
Revised 1 December 2009
Accepted 7 December 2009
Available online 16 December 2009
Acetylenes have attracted extensive attention in material sci-
ences1 such as acetylenic macrocycles2 and polyynes3 because they
diethyl chlorophosphate afforded yne-triyne 10 (Scheme 1). Tri-
yne-yne 8 was obtained as well in the same procedure. Triyne
derivatives 8 and 10 were pale yellow powdery compounds which
are stable in air and showed narrow melting points at 168–170 °C
and 198–200 °C, respectively. We name herein all these com-
pounds as follows: an acetylenic bond attached to the diphenylam-
inophenyl group precedes the remaining acetylenic bond.
possess abundant
p electrons and rigid arrays. We established a
double elimination protocol of b-substituted sulfones for access
to acetylenes,4 and disclosed the usefulness of this protocol for
the preparation of phenylene-ethynylene fluorophores.5 It was re-
vealed that amino-substituted fluorophores emit fluorescence
from their twisted intramolecular charge-transfer (TICT) states,
when UV-light is irradiated.6 Since the charge-separated excited
state is more stabilized in polar solvents than in less polar ones,
fluorescence undergoes bathochromic shift in polar solvents. Hira-
ta has already reported that aminoacetylenes 17 and 28 emit fluo-
rescence from intramolecular charge-separated states, but little is
known about emission of higher analogues. Herein we have pre-
pared various diphenylamino-substituted acetylenes in order to
X = H (1)
= CN (2)
H2N
X
Ph2N
n
monoyne 3 (n = 1)
diyne 4 (n = 2)
triyne 5 (n = 3)
evaluate the effect of acetylenic
p systems on optical properties
of amino-substituted phenylene-(poly)ethynylenes 3–10 (Fig. 1).
We have established a general route for the synthesis of amino-
substituted acetylenes,9 in which ethyne moiety and diyne and tri-
yne moieties are produced by the Sonogashira coupling10 and the
double elimination protocol of b-substituted sulfones,4 respec-
tively (Fig. 1). For instance, propargyl aldehyde 11 was prepared
by repeating the Sonogashira coupling and MnO2 oxidation, and
the addition of a THF solution of LiHMDS (lithium hexamethyldisi-
lazide) to a THF solution of propargyl sulfone 12, aldehyde 11, and
Ph2N
Ph2N
n
bisyne 6 (n = 1)
diyne-yne 7 (n = 2)
triyne-yne 8 (n = 3)
n
yne-diyne 9 (n = 2)
yne-triyne 10 (n = 3)
* Corresponding authors. Tel.: +86 731 8827 944; fax: +86 731 8827 944 (D.-L.A.);
tel.: +81 86 256 9533; fax: +81 86 256 4292 (A.O.).
E-mail addresses: deliean@sina.com (D.-L. An), orita@high.ous.ac.jp (A. Orita).
Figure 1. Structures of amino-substituted phenylene-(poly)ethynylenes.
0040-4039/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.tetlet.2009.12.023

918
J.-K. Fang et al. / Tetrahedron Letters 51 (2010) 917–920
I
Br
Pd(PPh3)4, CuI
Ph2N
Br
Ph2N
toluene, i-Pr2NH
rt, overnight
93 %
OH
OH
MnO2
CH2Cl2,
35 ºC,
Pd(PPh3)4, CuI
Ph2N
toluene, i-Pr2NH
60 ºC, overnight
83 %
overnight
Ph2N
Ph2N
CHO
11 81 %
ClP(O)(OEt)2,
LiHMDS
+
CHO
THF, 0 ºC-rt,
overnight
PhSO2
12
11
Ph2N
yne-triyne 10 15 %
ClP(O)(OEt)2,
LiHMDS
+
OHC
Ph2N
THF, 0 ºC-rt,
overnight
SO2Ph
14
13
Ph2N
triyne-yne 8 26 %
Scheme 1. Syntheses of yne-triyne 10 and triyne-yne 8.
Photochemical data such as UV–vis absorption and fluores-
10 as well: bisyne 6 (363 nm) ) diyne-yne 7 (395 nm) ) tri-
yne-yne (418 nm); bisyne 9
cence properties of these compounds are summarized in Table
1. UV absorption spectra of monoyne 3, diyne 4, and triyne 5
in cyclohexane (1.0 ꢀ 10ꢁ5 mol/L) exhibited their longest kmax at
345 nm, 372 nm, and 402 nm, respectively, and this bathochromic
8
6
(363 nm) ) yne-diyne
(391 nm) ) yne-triyne 10 (405 nm). When UV–vis spectra of 3–
10 were recorded in CH2Cl2 instead of cyclohexane, a little
difference was observed. These results show that there is no sol-
vent effect on UV–vis absorption of amino-substituted acetylenes
3–10.
shift could be explained by an expansion of acetylenic
p-conju-
gated systems. A similar bathochromic shift was observed in 6–
Table 1
UV-vis absorption and fluorescence properties of diphenylaminoacetylenes
monoyne 3
diyne 4
triyne 5
bisyne 6
diyne-yne 7
triyne-yne 8
yne-diyne 9
yne-triyne 10
UVa
c-C6H12
kmax [nm]
[L/mol cm])
345
(37,008)
372
(25,528)
402
(34,353)
363
(53,865)
395
(36,187)
418
(57,514)
391
(18,190)
405
(24,092)
(
e
CH2Cl2
kmax [nm]
351
372
401
373
392
418
385
401
(e
[L/mol cm])
(33,307)
(36,958)
(40,170)
(46,465)
(51,691)
(45,248)
(52,648)
(61,020)
PLb
c-C6H12
Emax [nm]
(
376
(0.43)
0.5
8.6, 11.4
0.75
394
(0.18)
0.4
4.5, 20.5
0.22
413
(<0.01)
397
(0.74)
0.9
8.2, 2.9
2.8
409
(0.34)
1.1
3.1, 6.0
0.52
427
(0.01)
408
(0.70)
0.7
10.0, 4.3
2.3
422
(0.04)
c
d
UF
se [ns]
)
kr, knr [108/s]
kr/knr
c
CH2Cl2
Emax [nm]
419
(0.78)
1.6
4.9, 1.4
3.5
447
(0.32)
3.0
1.1, 2.3
0.48
471
(0.01)
467
(0.89)
1.6
5.6, 0.69
8.1
478
(0.40)
0.7
5.7, 8.6
0.66
496
(0.01)
491
(0.86)
1.7
5.1, 0.82
6.2
523
(0.68)
1.7
4.0, 1.9
2.1
d
(
UF
se [ns]
)
kr, knr [108/s]
kr/knr
Df [nm]
43
53
58
70
69
69
83
101
a
b
c
d
e
f
UV–vis absorption in c-C6H12 and CH2Cl2 (1.0 ꢀ 10ꢁ5 M).
Fluorescence in c-C6H12 and CH2Cl2 (1.0 ꢀ 10ꢁ7 M).
Emission maximum.
Fluorescence quantum yield measured by integrated sphere system (Hamamatsu photonics C9920-02).
Fluorescence life time, solutions degassed by freeze-pump-thaw cycles, 5.0 ꢀ 10ꢁ6 M.
Difference of emission maxima in c-C6H12 and CH2Cl2.

J.-K. Fang et al. / Tetrahedron Letters 51 (2010) 917–920
919
Photoluminescence data of phenylene-(poly)ethynylenes 3–10
expansion of acetylenic
p
-system accelerates a radiationless pro-
such as wavelength and quantum yield are also summarized in Ta-
ble 1. Monoyne 3, diyne 4, and triyne 5 gave strong emission at
376 nm, 394 nm, and 413 nm in cyclohexane (1.0 ꢀ 10ꢁ7 mol/L),
respectively, and the emission maxima underwent bathochromic
cess with a radiation process suppressed to result in lower quan-
tum yields of diyne than those of monoyne both in
cyclohexane and CH2Cl2. It was found that in polar solvent CH2Cl2
= 8.9), although both radiation and radiationless processes were
suppressed, radiationless process was further suppressed. In less
polar solvent cyclohexane ( = 2.0), radiationless process was pre-
4
3
(e
shift by expansion of acetylenic
Quantum yields of these acetylenes decreased remarkably accord-
ing to the expansion of acetylenic -conjugated systems: mono-
p-conjugated system (Fig. 2).
e
p
dominant, and ratios of rate constants kr/knr were 0.75 for mono-
yne 3 (UF 0.43), diyne 4 (UF 0.18), triyne 5 (UF <0.01) (Table 1).
In CH2Cl2, these aminoacethylenes exhibited emission at longer
wavelengths than observed in cyclohexane (419 nm for monoyne
3, 447 nm for diyne 4, and 471 nm for triyne 5 (Fig. 2), and highly
yne 3 and 0.22 for diyne 4. In contrast to this, in more polar
solvent CH2Cl2 (e = 8.9), rate constants kr/knr increased to 3.5
(monoyne 3) and 0.48 (diyne 4) giving rise to higher quantum
yields of 3 and 4, although radiation rate constant kr in CH2Cl2
was remarkably smaller than in cyclohexane.
expanded p-system diyne 4 and triyne 5 underwent larger solvent
effect on wavelengths of emission maxima: differences of emission
maxima in cyclohexane and CH2Cl2.were 43 nm for 3, 53 nm for 4,
and 58 nm for 5. These bathochromic shifts observed by changing
solvent polarities can be explained in terms of stabilization of the
charge-separated excited states of aminoacetylenes which are gen-
erated by irradiation of UV-light. In the excited state, amino-
substituted acetylenes undergo intramolecular charge transfer giv-
ing rise to a positive charge on the amino group and a negative
charge on phenylene-(poly)ethynylene moieties. The charge-sepa-
rated excited state can be stabilized more efficiently than the
ground state in polar solvent such as CH2Cl2 resulting in batho-
chromic shift of emission maxima. Aminoacetylenes 3 and 4 indi-
cated larger quantum yields in CH2Cl2 than in cyclohexane;
monoyne 3 (0.78 vs 0.43) and diyne 4 (0.32 vs 0.18). In order to
investigate in the emission mechanism, fluorescence life times
When UV-light was irradiated to solutions of bisyne 6, diyne-
yne 7, triyne-yne 8, yne-diyne 9, and yne-triyne 10, a strong
emission was recorded both in cyclohexane and CH2Cl2 (Fig. 3, Ta-
ble 1). In cyclohexane, aminoacetylenes 7–10 underwent batho-
chromic shift in comparison with 6 because of their larger
expanded acetylenic p-systems. When photoluminescence spectra
of 7–10 were recorded in CH2Cl2, it was found that yne-diyne 9
and yne-triyne 10 exhibited a larger bathochromic shift than 6–
8: differences of emission maxima in cyclohexane and CH2Cl2 (D)
were 83 nm for 9 and 101 nm for 10, but
D
values for 6–8 were less
H2N
(s
) of 3 and 4 were recorded in cyclohexane and in CH2Cl2, and rate
constants for radiation process kr, and radiationless process knr
were calculated based on the following equations [kr = UF
MO 100
/s,
S0
S2
knr = (1 ꢁ UF)/
s] (Table 1). Comparison of kr and knr reveals that
287.14 nm (f = 0.0000),
0.44533 (contribution of transition
from MO 88 to MO100)
MO 90 (LUMO)
monoyne 3 (C6H12)
monoyne 3 (CH2Cl2)
diyne 4 (C6H12)
diyne 4 (CH2Cl2)
triyne 5 (C6H12)
1
0.8
0.6
0.4
0.2
291.46 nm (f = 1.3107)
S0
S1
0.42157 (contribution of transition
from MO 89 to MO90)
triyne 5 (CH2Cl2)
MO 89 (HOMO)
MO 88
0
350
400
450
500
550
600
wavelength [nm]
Figure 4. Result of theoretical calculation for NH2-yne-triyne in the excited state.
Figure 2. Emission spectra of 3–5 in c-hexane and CH2Cl2.
S2
1
0.8
0.6
0.4
0.2
0
bisyne 6 (C6H12)
bisyne 6 (CH2Cl2)
S1
diyne-yne 7 (C6H12)
diyne-yne 7 (CH2Cl2)
triyne-yne 8 (C6H12)
triyne-yne 8 (CH2Cl2)
yne-diyne 9 (C6H12)
yne-diyne 9 (CH2Cl2)
yne-triyne 10 (C6H12)
yne-triyne 10 (CH2Cl2)
emission
h
ν
S0
350
400
450
500
550
600
650
wavelength [nm]
Figure 5. Energy diagram of NH2-yne-triyne in the ground state and the excited
Figure 3. Emission spectra of 6–10 in c-hexane and CH2Cl2.
state.

920
J.-K. Fang et al. / Tetrahedron Letters 51 (2010) 917–920
than 70 nm. Such larger solvent effects observed in 9 and 10 indi-
cate that diyne and triyne moieties located at the opposite side of
amino group could accommodate a negative charge efficiently
which was generated in the excited state. Comparison of ratios of
rate constants (kr/knr) of 6, 7, and 9 revealed that radiation process
became more predominant in CH2Cl2 than in cyclohexane resulting
in higher quantum yields (UF). Surprisingly, emission of yne-triyne
10 was remarkably enhanced in CH2Cl2: UF(CH2Cl2) = 0.68,
UF(c-C6H12) = 0.04).
References and notes
1. (a) Acetylene Chemistry: Chemistry, Biology, and Material Science; Diederich, F.,
Stang, P. J., Tykwinski, R. R., Eds.; VCH: Weinheim, 2005; (b)Modern Acetylene
Chemistry; Stang, P. J., Diederich, F., Eds.; VCH: Weinheim, 1995.
2. For recent reviews on dehydrobenzoannulenes: (a) Tobe, Y.; Sonoda, M. In
Modern Cyclophane Chemistry; Gleiter, R., Hopf, H., Eds.; Wiley-VCH: Weinheim,
Germany, 2004. p 1; (b) Jones, C. S.; O’Connor, M. J.; Haley, M. M. In Acetylene
Chemistry: Chemistry, Biology and Material Science; Diederich, F., Stang, P. J.,
Tykwinski, R. R., Eds.; Wiley-VCH: Weinheim, Germany, 2005. p. 303; (c)
Spitler, E. L.; Johnson, C. A., II; Haley, M. M. Chem. Rev. 2006, 106, 5344.
3. For recent reviews: (a) Marsden, J. A.; Palmer, G. J.; Haley, M. M. Eur. J. Org.
Chem. 2003, 2355; (b) Haley, M. M. Synlett 1998, 557; (c) Haley, M. M.; Wan, W.
B.. In Advances in Strained and Interesting Organic Molecules; Halton, B., Ed.; JAI
Press: New York, 2000; Vol. 8, p 1; (d) Bunz, U. H. F.; Rubin, Y.; Tobe, Y. Chem.
Soc. Rev. 1999, 28, 107.
4. (a) Doi, T.; Orita, A.; Matsuo, D.; Saijo, R.; Otera, J. Synlett 2008, 55; (b) Orita, A.;
Taniguchi, H.; Otera, J. Chem. Asian J. 2006, 1, 430; (c) Orita, A.; Nakano, T.;
Yokoyama, T.; Babu, G.; Otera, J. Chem. Lett. 2004, 33, 1298; (d) Orita, A.;
Miyamoto, K.; Nakashima, M.; Ye, F.; Otera, J. Adv. Synth. Catal. 2004, 346, 767;
(e) Ye, F.; Orita, A.; Yaruva, J.; Hamada, T.; Otera, J. Chem. Lett. 2004, 33, 528; (f)
Ye, F.; Orita, A.; Doumoto, A.; Otera, J. Tetrahedron 2003, 59, 5635; (g) Orita, A.;
Ye, F.; Doumoto, A.; Otera, J. Chem. Lett. 2003, 32, 104.
Finally, in order to get better insight into the excited state of
yne-triyne 10, which exhibited the largest solvent effect of batho-
chromic shift (
D
) and enhanced quantum yield (UF), theoretical
*
calculations (CIS/6-31+G ) were carried out for a model molecule
NH2-yne-triyne.11 The lowest excited state (S1) mainly results
from electron-transition from HOMO (MO89) to LUMO (MO90)
(Fig. 4). The secondary excited state (S2) resulting from MO88 to
MO100 transition, lies close to the S1 state. Although MO88 is a
p
molecular orbital expanded over the whole molecule, MO100 is
5. (a) Mao, G.; Orita, A.; Matsuo, D.; Hirate, T.; Iwanaga, T.; Toyota, S.; Otera, J.
Tetrahedron Lett. 2009, 50, 2860; (b) Mao, G.; Orita, A.; Fenenko, L.; Yahiro, M.;
Adachi, C.; Otera, J. Mater. Chem. Phys. 2009, 115, 378; (c) Ding, C.; Babu, G.;
Orita, A.; Hirate, T.; Otera, J. Synlett 2007, 2559; (d) An, D.-L.; Zhang, Z.; Orita,
A.; Mineyama, H.; Otera, J. Synlett 2007, 1909; (e) Fenenko, L.; Shao, G.; Orita,
A.; Yahiro, M.; Otera, J.; Svechnikov, S.; Adachi, C. Chem. Commun. 2007, 2278;
(f) Shao, G.; Orita, A.; Nishijima, K.; Ishimaru, K.; Takezaki, M.; Wakamatsu, K.;
Gleiter, R.; Otera, J. Chem. Asian J. 2007, 2, 489; (g) Shao, G.; Orita, A.; Taniguchi,
H.; Ishimaru, K.; Otera, J. Synlett 2007, 231; (h) Shao, G.; Orita, A.; Nishijima, K.;
Ishimaru, K.; Takezaki, M.; Wakamatsu, K.; Otera, J. Chem. Lett. 2006, 35, 1284.
6. Chapter 3 in Molecular Fluorescence: Principles and Applications; Valeur, B., Ed.;
VCH: Weinheim, 2001.
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.
9. Full experimental procedures and characterization of all the products are
shown in Supplementary data.
10. (a) Sonogashira, K.; Tohda, Y.; Hagihara, N. Tetrahedron Lett. 1975, 4467; (b)
Tohda, Y.; Sonogashira, K.; Hagihara, N. Synthesis 1977, 777; (c) Takahashi, S.;
Kuroyama, Y.; Sonogashira, K.; Hagihara, N. Synthesis 1980, 627; For a most
recent review: Chinchilla, R.; Nájera, C. Chem. Rev. 2007, 107, 874.
localized on triyne moiety and perpendicular to HOMO and LUMO.
The geometry optimization of the excited states revealed that the
energy order of the S1 and S2 states was inverted at the stationary
point (Fig. 5).12 Therefore, the internal conversion of the excited
state (S1?S2) would easily occur13 and induce higher polarization
of NH2-yne-triyne in the excited state S2 resulting in great solvent
effect of fluorescence.14
We succeeded in preparation of a variety of amino-substituted
phenylene-(poly)ethynylenes by a combination of Sonogashira
coupling and double elimination of b-substituted sulfones. The
phenylene-(poly)ethynylenes exhibited strong absorption bands
in UV–vis spectroscopy, and emitted strong fluorescence when
UV-light was irradiated. In CH2Cl2, the phenylene-(poly)ethynyl-
enes showed bathochromic shifts of emission in comparison with
emission in cyclohexane. Theoretical calculations suggested that
amino-substituted yne-triyne undergo high polarization in its ex-
cited state resulting in large bathochromic shift through intercon-
version of excited states. Further study in optical properties of
11. Theoretical calculations were carried out on NH2-yne-triyne with three
benzene rings fixed in the same plane by using GAUSSIAN 03 (Gaussian, Inc.).
12. Higher level of calculations including electron correlation will be carried out
for further quantitative investigation.
amino-substituted acetylenic
p-system and their application for
13. The energy barrier of rotation for diphenyltriyne moiety of NH2-yne-triyne in
ground state is significantly low: free energy difference between its planar and
design of organic light-emitting materials are under investigation.
*
orthogonal forms is calculated as 0.038 kcal molꢁ1 by B3LYP/6-31+G , and the
former is more stable. Although higher level of theoretical calculation is
required for further investigation in the excited states S1 and S2, the symmetry
Acknowledgments
breaking induced by the rotational vibration would allow the S1?S2 internal
*
conversion. It was reported that, intrinsically perpendicular the
underwent internal conversion to n,
p–
p
state
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 Technol-
ogy), Japan, and Okayama Prefecture Industrial Promotion
Foundation.
*
p state: Ismail, N.; Blancafort, L.; Olivucci,
M.; Kohler, B.; Robb, M. A. J. Am. Chem. Soc. 2002, 124, 6818.
14. It was reported that azulenes emit fluorescence from S2. For instance: (a) Birks,
J. B. Chem. Phys. Lett. 1972, 17, 370; (b) Viswath, G.; Kasha, M. J. Chem. Phys
1956, 24, 757.
Supplementary data
Supplementary data (full synthetic details and characterization
of acetylenic compounds) associated with this article can be found,
in the online version, at doi:10.1016/j.tetlet.2009.12.023.