Position of substitution: A facile way to tune the spectroscopic properties of dimethylamino-substituted arylene-ethynylenes

Article abstract of DOI:10.3184/174751915X14383380888501

A series of dimethylamino-substituted arylene-ethynylenes were synthesised by Sonogashira coupling reactions and characterised by the methods of 1H, 13C NMR, UV-Vis, fluorescence, HRMS and theoretical calculations. Effects on spectroscopic properties caus

Full text of DOI:10.3184/174751915X14383380888501

JOURNAL OF CHEMICAL RESEARCH 2015
VOL. 39 AUGUST, 487–491
RESEARCH PAPER 487
Position of substitution: a facile way to tune the spectroscopic properties of
dimethylamino-substituted arylene-ethynylenes
Jing-Kun Fang*, Tengxiao Sun, Yu Fang, Zhimin Xu, Hui Zou, Yuan Liu and Fangting Ge
School of Chemical Engineering, Nanjing University of Science and Technology, Xiaolingwei Street No. 200, Nanjing 210094, P.R. China
A series of dimethylamino-substituted arylene-ethynylenes were synthesised by Sonogashira coupling reactions and characterised by
the methods of 1H, 13C NMR, UV-Vis, fluorescence, HRMS and theoretical calculations. Effects on spectroscopic properties caused by the
different positions of the dimethylamino group in arylene-ethynylenes were studied and discussed. The shortest absorption maximum, the
largest Stokes shift and the highest fluorescence efficiency were observed for arylene-ethynylenes with a dimethylamino group present
in the ortho-position.
Keywords: arylene-ethynylenes, dimethylamino, organic dyes, spectroscopic properties, Stokes shift, position of substitution
Organic dyes have been widely applied in solar energy
conversion,1 fluorescent probes,2 biological chemistry,3 light-
harvesting/emitting materials4 and nanoscience.5 An ideal
dye has an adjustable absorption/emission spectra, high molar
extinction coefficient and fluorescence efficiency, a large Stokes
shift and good stability. However, there are few dye molecules
with outstanding performance in all aspects. The undesirable
properties of organic dyes will restrict their potential applications.
For example, the small Stokes shift of boron dipyrromethane
(BODIPY) will result in a self-quenching, which is detrimental
for fluorescence response.6 Thus, it is important to find the
crucial factors that affect these key properties of dyes.
by alternating the locations of the ethynylene moiety.11,12 Amino
groups are widely adopted in functional molecules in many
fields, but amino groups were only located at the para-position
in most cases.13-15 It is important to investigate the changes in
spectroscopic properties influenced by the different positions
of the amino substituents, with the aim of scrutinising the
properties of the amino-substituted molecules. In this paper,
arylene-ethynylenes with a dimethylamino group substituted at
the para, meta- and ortho- positions were synthesised, numbered
1a–c and 2a–c (Scheme 1). Their spectroscopic properties were
studied and theoretical calculations on these molecules have been
performed.
Arylene-ethynylenes are
a
common architecture for
Results and discussion
dyes and have attracted extensive attention in fluorescent
materials, optoelectrical materials, liquid crystal materials
and dye-sensitised solar cells.7-10 We have reported a series of
diphenylamino-substituted phenylene-(poly)ethynylenes. A large
bathochromic shift and thus a large Stokes shift were observed
Absorption spectra: The absorption spectra of arylene-
ethynylenes 1a–c and 2a–c in dilute CH2Cl2 solution ( 2.0 × 10-4
M ) are shown in Figs 1 and 2, respectively. The data are listed
in Table 1.
I
(1.2 equiv.)
TMS (1.2 equiv.)
K2CO3
Pd(PPh3)4/CuI
Pd(PPh3)4/CuI
Me2N
Br
Me2N
TM
S
S
Me2N
NMe2
Toluene/ i-Pr2NH
THF/CH3OH
Toluene/ i-Pr2NH
para-
3a
4a
2a
2b
I
(1.2 equiv.)
Me2N
Me2N
Me2N
NMe2
meta-
TMS (1.2 equiv.)
K2CO3
Pd(PPh3)4/CuI
Pd(PPh3)4/CuI
Br
TM
Toluene/ i-Pr2NH
THF/CH3OH
Toluene/ i-Pr2NH
3b
4b
I
(1.2 equiv.)
NMe2
Br
NMe2
NMe2
Me2N
TMS (1.2 equiv.)
ortho-
K2CO3
Pd(PPh3)4/CuI
Pd(PPh3)4/CuI
TM
S
Toluene/ i-Pr2NH
THF/CH3OH
Toluene/ i-Pr2NH
3c
4c
2c
4a
Pd(PPh3)4/CuI
NMe2
para-
Toluene/ i-Pr2NH
1a
1b
I
I (3.0 equiv.)
NMe2
meta-
4b
Pd(PPh3)4/CuI
Pd(PPh3)4/CuI
I
Toluene/ i-Pr2NH
Toluene/ i-Pr2NH
5
(1.1 equiv.)
Me2N
4c
ortho-
Pd(PPh3)4/CuI
Toluene/ i-Pr2NH
1c
Scheme 1 Synthesis of 1a–c and 2a–c.
* Correspondent. E-mail: fjk_003@163.com

488 JOURNAL OF CHEMICAL RESEARCH 2015
60000
50000
40000
30000
20000
10000
0
1a
1b
1c
BPEB
2a
2b
2c
30000
20000
10000
0
250
300
350
400
450
250
300
350
400
450
Wavelength (nm)
Wavelength(nm)
Fig. 1 Absorption spectra of 1a–c and 1,4-bis(phenylethynyl)benzene (BPEB).
Fig. 2 Absorption spectra of 2a–c.
Table 1 Absorption and fluorescence data of 1a–c and 2a–c
Due to the steric effects of the dimethylamino group with the
phenylethynyl moiety, 1c cannot achieve coplanarity, which
limits the extent of conjugation. Finally, a bathochromic shift
is also not observed for 1c. This will be further discussed in the
theoretical calculations.
Compound
Stokes shift/nm
λ
abs/nm(log ε)
λ
em/nma
ΦF
1a
1b
1c
2a
2b
2c
363(4.64)
320(4.70)
320(4.65)
331(4.51)
270(4.56)
260(4.24)
468
470
468
392
409
411
105
150
148
61
139
151
0.78
0.32
0.87
0.04
0.21
0.76
Similarly, the absorption maximum (λ ) of 2a (331 nm)
also appears at a longer wavelength than atbhs ose of 2b and 2c
(270 nm and 260 nm). The steric effects of the dimethylamino
group with the phenylethynyl moiety is more remarkable in
a limited conjugation range. So, 2c exhibits the shortest λabs
and the weakest intensity of the absorption among these three
compounds. In the absorption spectra of 2b and 2c, both the E2
and the B band can be observed. But in the absorption spectrum
of 2a, in which the dimethylamino group was introduced in the
para-position as an auxochrome, the E2 band shows a greater
bathochromic shift than the B band. As a result, the B band and
the E2 band overlap and only one absorption can be observed.
Emission spectra: The emission spectra of arylene-
ethynylenes 1a–c and 2a–c in dilute CH2Cl2 solution (1.0 × 10-6
M) are shown in Figs 3 and 4, respectively. The data are listed in
Table 1. It is clear that the positon of the dimethylamino group
shows no influence on the emission peak wavelength (λem) for
1a–c, and that the λem of 2a with a dimethylamino group present
in the para-position shows a hypsochromic shift of less than 20
nm compared to λem of 2b and 2c with a dimethylamino group
present in the meta- and ortho- position, respectively.
a Excited at the longest absorption maxima.
It is clear that the absorption maximum (λabs) of 1a (363 nm)
appears at a longer wavelength than those of 1b and 1c (320 nm
and 320 nm). The dimethylamino group is an auxochrome with
nonbonded electrons and16 if this group is in direct conjugation
with the π-system of the chromophore, it may increase the
wavelength at which the light is absorbed. By attaching a
dimethylamino group to 1,4-bis(phenylethynyl)benzene
(λ = 320nm in CH2Cl2, Fig. 1) to the para-position (1a), a
baatbhsochromic shift of 43 nm was observed. That is to say, it
modifies the ability of 1,4-bis(phenylethynyl)benzene to absorb
light. If an auxochrome is present in the meta- position to the
chromophore, it does not affect the colour. That is the reason
why the absorption spectrum of 1b shows no bathochromic
shift compared to that of 1,4-bis(phenylethynyl)benzene.
1.0
1.0
2a
1a
2b
2c
1b
1c
0.5
0.5
0.0
0.0
400
450
500
550
350
400
450
500
Wavelength(nm)
Wavelength(nm)
Fig. 3 Emission spectra of 1a–c.
Fig. 4 Emission spectra of 2a–c.

JOURNAL OF CHEMICAL RESEARCH 2015 489
NMe2
NMe2
HOMO
LUMO
。
。
1a
1b
0.0
0.2
2a
2b
0.0
NMe2
NMe2
2a
2b
。
。
0.2
Me2N
Me2N
。
。
9.9
1c
9.1
2c
Fig. 6 Calculated dihedral angles between the neighbouring benzene
rings in the optimised geometries of 1a–c and 2a–c.
2c
π-system of the chromophore in these two molecules. This is
why shorter wavelength absorption maxima are observed for 1b
and 2b.
1a
1b
1c
Figure 6 shows the optimised ground-state geometries of
arylene-ethynylenes 1a–c and 2a–c with the dihedral angles
between two neighbouring benzene rings indicated. The
dimethylamino-substituted benzene rings are coplanar with the
phenylene acetylene units in 1a, 1b, 2a and 2b, but for 1c and 2c
there is a twist between the dimethylamino substituted benzene
rings and the phenylene acetylene units (9.1° for 1c, 9.9° for
2c), which restricts the conjugation within these two molecules
resulting in shorter wavelength absorption maxima.
Experimental
Melting points were measured on an XRC-1 apparatus. H NMR
1
Fig. 5 HOMOs and LUMOs of 1a–c and 2a–c.
and 13C NMR spectra were recorded at room temperature on JEOL
Lambda 500 instruments with tetramethylsilane as an internal
reference. Mass spectra were recorded on a Waters Q-TOF MicroTM
spectrometer. Elemental analysis was performed with a Yanagimoto
MT3CHN instrument. UV-Vis absorption spectra and emission
spectra were recorded by HITACHI U-3310 and JASCO FP-6600
at room temperature, respectively. Absolute quantum yields of
photoluminescence were recorded by an integration sphere system
(Hamamatsu photonics C9920-02). All reactions were carried out
under an atmosphere of nitrogen with freshly distilled solvents
and all reagents were obtained from commercial sources and used
without further purification, unless otherwise noted. Toluene and
diisopropylamine were distilled from CaH2. Compounds 5 and 2a–c
were prepared according to the corresponding literature methods.11,18-20
The results above indicate that arylene-ethynylenes with a
dimethylamino group present in the meta- and ortho- position
show shorter λabs than those with the group in the para-position,
while the value of their λem is similar. As a result, remarkable
Stokes shifts (139–151 nm) are observed within arylene-
ethynylenes with a dimethylamino group present in the meta-
and ortho- position (1b, 1c, 2b and 2c). It is noteworthy that
a particularly large Stokes shifts (151 nm) in 2c was observed
with such a limited conjugation extent of two benzene rings.
These interesting results prompted us to carry out further
investigations. The fluorescence efficiency (ΦF) of 1a–c and
2a–c in CH2Cl2 were measured. As is shown in Table 1, 1c and 2c
with a dimethylamino group present in the ortho- position each
show the highest fluorescence efficiency in the corresponding
series, 0.87 and 0.76, respectively. Based on the above results,
arylene-ethynylenes with a dimethylamino group present in the
ortho- position would show the shortest absorption maxima, the
largest Stokes shift and the highest fluorescence efficiency.
Theoretical calculations: To investigate the geometrical
and photophysical properties, molecular orbital calculations of
arylene-ethynylenes 1a–c and 2a–c were carried out using DFT
calculations with the Gaussian 09 program.17 Full geometrical
optimisations were performed and all of the calculations were
performed with the B3LYP exchange correlation functional
under the 6-31G (d) basis set.
Synthesis of N,N-dimethyl-[(trimethylsilyl)ethynyl]anilines (3a–c);
general procedure
Bromo-N,N-dimethylaniline (400 mg, 2.0 mmol), (trimethylsilyl)
acetylene (236 mg, 2.4 mmol), Pd(PPh3)4 (116 mg, 0.1 mmol), CuI (19
mg, 0.1 mmol), diisopropylamine (5 mL) and toluene (15 mL) were
added to a flask and the mixture was stirred at 80 °C overnight. Then
the reaction mixture was poured into saturated NH4Cl (50 mL) and
extracted with CH2Cl2 (3 x 20 mL), the organic layer was washed with
saturated brine (1 x 50 mL) and dried over MgSO4. After filtration,
o
solvents were removed by rotary evaporation (40–45 C). The crude
product was subjected to column chromatography (SiO2; eluent,
hexane/ CH2Cl2, 3:1) to give the corresponding compounds.
N,N-Dimethyl-4-[(trimethylsilyl)ethynyl]aniline (3a): Pale yellow
powder; yield 74%, m.p. 86–88 °C (lit.21 88–89 °C). 1H NMR (500
MHz, CDCl3): δ 0.23(s, 9H), 2.97(s, 6H), 6.59(d, J = 9.0 Hz, 2H),
7.34(d, J = 9.0 Hz, 2H).
The HOMOs and LUMOs of arylene-ethynylenes 1a–c and
2a–c are shown in Fig. 5, the isodensity surface values are fixed
at 0.03. It can be seen that from HOMO to LUMO, all of these
arylene-ethynylenes exhibit a tendency for the electron density
geometry distributions to move from the dimethylamino
group to the phenylene acetylene units. Obviously, the
electron distribution of the HOMOs of 1b and 2b indicate that
dimethylamino groups are not well conjugated with the whole
N,N-Dimethyl-3-[(trimethylsilyl)ethynyl]aniline (3b): Pale yellow
1
oil; yield 84%. H NMR (500 MHz, CDCl3): δ 0.25(s, 9H), 2.94(s,
6H), 6.69(d, J = 7.0 Hz, 1H), 6.81–6.84(m, 2H), 7.15(t, J = 8.0 Hz,
1H). (lit.22 1H NMR (300 MHz, CDCl3): δ 0.25(s, 9H), 2.93 (s, 6H),
6.66–6.71 (m, 1H), 6.79-6.85 (m, 2H), 7.10–7.17 (m, 1H).

490 JOURNAL OF CHEMICAL RESEARCH 2015
N,N-Dimethyl-2-[(trimethylsilyl)ethynyl]aniline (3c): Pale yellow
oil; yield 81%. H NMR (500 MHz, CDCl3): δ 0.26(s, 9H), 2.95(s,
6H), 6.81–6.87(m, 2H), 7.22(t, J = 7.5 Hz, 1H), 7.42(d, J = 7.5 Hz, 1H).
(lit.23 1H NMR (400 MHz, CDCl3): δ 0.26 (s, 9H), 2.95 (s, 6H), 6.83 (td,
J = 7.6, 0.8 Hz, 1H), 6.86(d, J = 8.4 Hz, 1H), 7.20–7.24 (m, 1H), 7.42
(dd, J = 7.6, 1.6 Hz, 1H).
6.71(dd, J = 8.0 Hz, J = 1.5 Hz, 1H), 6.89–6.91(m, 2H), 7.20(t, J =
8.0 Hz, 1H), 7.29–7.35(m, 3H), 7.54(dd, J = 8.0 Hz, J = 1.5 Hz, 2H).
13C NMR (125 MHz, CDCl3): δ 40.5, 88.2, 90.3, 112.8, 115.2, 119.9,
123.4, 123.5, 128.0, 128.3, 129.0, 131. 6, 150.3. Anal. calcd for C16H15N:
C, 86.84; H, 6.83; N, 6.33; found: C, 86.61; H, 6.86; N, 6.28%. (lit.19
1H NMR (400 MHz, CDCl3): δ 2.97 (s, 6H), 6.71–6.74(m, 1H), 6.92 (d,
J = 7.4 Hz, 2H), 7.22 (t, J = 7.7 Hz, 1H), 7.32–7.35(m, 3H), 7.54–7.56
(m, 2H); 13C NMR (100 MHz, CDCl3): δ 40.4, 88.2, 90.3, 112.8, 115.2,
119.9, 123.4, 123.5, 128.0, 128.2, 129.0, 131.5,150.3).
1
Synthesis of ethynyl-N,N-dimethylanilines (4a–c); general procedure
Compound 3 (326 mg, 1.5 mmol), K2CO3 (2.073 g, 15.0 mmol), THF
(5 mL) and MeOH (5 mL) were added to a flask, and the mixture
was stirred at room temperature for 2 h. Then the reaction mixture
was poured into water (50 mL) and extracted with CH2Cl2 (3 x 20
mL), the organic layer was washed with saturated brine (1 x 50 mL)
and dried over MgSO4. After filtration, the solvent was removed in a
rotary evaporator (40–45 oC) were evaporated. The crude product was
subjected to column chromatography (SiO2; eluent, hexane/ CH2Cl2,
3:1) to give the corresponding compounds.
4-Ethynyl-N,N-dimethylaniline (4a): Pale yellow powder; yield
98.2%, m.p. 50–51°C (lit.24 51–52°C). 1H NMR (500 MHz, CDCl3): δ
2.96(s, 6H), 2.97(s, 1H), 6.62(d, J = 9.0 Hz, 2H), 7.36(d, J = 9.0 Hz, 2H).
3-Ethynyl-N,N-dimethylaniline (4b): Pale yellow oil; yield 94.6%.
1H NMR (500 MHz, CDCl3): δ 2.95(s, 6H), 3.01(s, 1H), 6.72(d, J =
9.0 Hz, 1H), 6.85–6.86(m, 2H), 7.17(t, J = 8.0 Hz, 1H). (lit.24 1H NMR
(CDCl3): δ 2.94 (s, 6H), 3.01 (s, 1H), 6.71 (d, J = 8.1 Hz, 1H), 6.82–6.90
(m, 2H), 7.17 (td, J = 8.1, 0.8 Hz, 1H).
N,N-Dimethyl-2-(phenylethynyl)aniline (2c): Pale yellow oil; yield
1
52%. H NMR (500 MHz, CDCl3): δ 2.99(s, 6H), 6.89(t, J = 8.0 Hz,
1H), 6.92(d, J = 8.0 Hz, 1H), 7.24(t, J = 8.0 Hz, 1H), 7.28–7.35(m,
3H), 7.49(dd, J = 8.0 Hz, J = 1.5 Hz, 1H), 7.54(dd, J = 8.0 Hz, J = 1.5
13
Hz, 2H)； C NMR (125 MHz, CDCl3): δ 43.4, 88.8, 94.7, 115.0, 116.9,
120.4, 123.8, 128.0, 128.3, 129.2, 131.2, 134.2, 154.7. Anal. calcd for
C16H15N: C, 86.84; H, 6.83; N, 6.33; found: C, 86.57; H, 6.77; N, 6.28%.
(lit.20 1H NMR (400 MHz, CDCl3): δ 3.01 (s, 6H), 6.88–6.94 (m, 2H),
7.25 (t, J = 6.3 Hz, 1H), 7.31–7.37 (m, 3H), 7.49 (d, J = 5.7 Hz, 1H),
7.54 (d, J = 7.2 Hz, 2H); 13C NMR (100 MHz, CDCl3): δ 43.8, 89.1,
95.0, 115.3, 117.2, 120.7, 124.1, 128.2, 128.5, 129.5, 131.5, 134.6, 155.0).
N,N-Dimethyl-4-{[4-(phenylethynyl)phenyl]ethynyl}aniline (1a):
Pale yellow powder; yield 81%, m.p. 207–209°C. 1H NMR (500 MHz,
CDCl3): δ 2.98(s, 6H), 6.65(d, J = 9.0 Hz, 2H), 7.32–7.36(m, 3H),
7.41(d, J = 9.0 Hz, 2H), 7.44–7.50(m, 4H), 7.52–7.54(m, 2H). 13C NMR
(125 MHz, CDCl3): δ 40.2, 87.3, 89.4, 90.8, 92.8, 109.7, 111.8, 122.1,
123.2, 124.1, 128.3, 128.3, 131.1, 131.4, 131.6, 132.8, 150.2. HRMS
(ESI+) m/z: calcd for (M+H)+ C24H20N: 322.1591, found: 322.1588.
Anal. calcd for C24H19N: C, 89.68; H, 5.96; N, 4.36; found: C, 89.52; H,
5.90; N, 4.32%.
N,N-Dimethyl-3-{[4-(phenylethynyl)phenyl]ethynyl}aniline
(1b): Pale yellow powder; yield 92%, m.p. 186–188°C. 1H NMR
(500 MHz, CDCl3): δ 2.97(s, 6H), 6.65(dd, J = 8.0 Hz, J = 2.5 Hz,
1H), 6.89–6.91(m, 2H), 7.21(t, J = 8.0 Hz, 1H), 7.34–7.37(m, 3H),
7.49–7.54(m, 6H). 13C NMR (125 MHz, CDCl3): δ 40.5, 88.0, 89.2,
91.1, 92.3, 113.1, 115.3, 112.0, 122.9, 123.1, 123.4, 123.4, 128.4, 128.4,
129.1, 131.5, 131.5, 131.6, 150.4. HRMS (ESI+) m/z: calcd for (M+H)+
C24H20N: 322.1591, found: 322.1590. Anal. calcd for C24H19N: C, 89.68;
H, 5.96; N, 4.36; found: C, 89.51; H, 5.88; N, 4.26%.
2-Ethynyl-N,N-dimethylaniline (4c): Pale yellow oil; yield 91.1%.
1H NMR (500 MHz, CDCl3): δ 2.93(s, 6H), 3.43(s, 1H), 6.89(t, J = 7.5
Hz, 1H), 6.94(d, J = 8.5 Hz, 1H), 7.28(t, J = 8.5 Hz, 1H), 7.46(d, J =
7.5 Hz, 1H). (lit.23 1H NMR (400 MHz, CDCl3): δ 2.93 (s, 6H), 3.42
(s, 1H), 6.88 (td, J = 7.6, 1.2 Hz, 1H), 6.93 (dd, J = 8.4, 1.2 Hz, 1H),
7.25–7.29 (m, 1H), 7.46 (dd, J = 7.6, 1.6 Hz, 1H).
Synthesis of 1-iodo-4-(phenylethynyl)benzene (5)
1,4-Diiodobenzene (990 mg, 3.0 mmol), phenylacetylene (102 mg,
1.0 mmol), Pd(PPh3)4 (58 mg, 0.05 mmol), CuI (10 mg, 0.05 mmol),
diisopropylamine (5 mL) and toluene (15 mL) were added to a flask
and the mixture was stirred at room temperature overnight. Then the
reaction mixture was poured into saturated NH4Cl and extracted with
CH2Cl2 (3 x 20 mL), the organic layer was washed with saturated
brine (1 x 50 mL) and dried over MgSO4. After filtration, solvent was
N,N-Dimethyl-2-{[4-(phenylethynyl)phenyl]ethynyl}aniline (1c):
1
Pale yellow powder; yield 63%, m.p. 65–66°C. H NMR (500 MHz,
o
removed in a rotary evaporator (40–45 C). The crude product was
CDCl3): δ 2.99(s, 6H), 6.89(t, J = 7.5 Hz, 1H), 6.92(d, J = 8.5 Hz, 1H),
7.25(d, J = 8.5 Hz, 1H), 7.32–7.35(m, 3H), 7.48–7.54(m, 7H). 13C NMR
(125 MHz, CDCl3): δ 43.5, 89.2, 90.8, 91.1, 94.4, 114.7, 116.9, 120.4,
122.7, 123.0, 123.6, 128.3, 128.4, 129.4, 131.1, 131.5, 131.6, 134.3,
154.7. HRMS (ESI+) m/z: calcd for (M+H)+ C24H20N: 322.1591, found:
322.1601. Anal. calcd for C24H19N: C, 89.68; H, 5.96; N, 4.36; found: C,
89.44; H, 5.87; N, 4.29%.
subjected to column chromatography (SiO2; eluent, hexane) to give 5
as a white powder; yield 78%. 1H NMR (500 MHz, CDCl3): δ 7.26(d,
J = 8.5 Hz, 2H), 7.34–7.37(m, 3H), 7.51–7.54(m, 2H), 7.69(d, J = 8.5
Hz, 2H). (lit.25 1H NMR (400 MHz, CDCl3): δ 7.24 (d, J = 8.4 Hz, 2H),
7.33–7.35 (m, 3H), 7.50–7.52 (m, 2H), 7.67 (d, J = 8.4 Hz, 2H).
Synthesis of N,N-dimethyl-(phenylethynyl)anilines (2a–c) and N,N-
dimethyl-{[(4-(phenylethynyl)phenyl]ethynyl}anilines (1a–c); general
procedure
Conclusions
Compound 4 (145 mg, 1.0 mmol), iodobenzene (245 mg, 1.2 mmol) or
5 (335 mg, 1.1 mmol), Pd(PPh3)4 (58 mg, 0.05 mmol), CuI (10 mg, 0.05
mmol), diisopropylamine (3 mL) and toluene (10 mL) were added to
the flask and the mixture was stirred at room temperature overnight.
Then the reaction mixture was poured into saturated NH4Cl and
extracted with CH2Cl2 (3 x 20 mL), the organic layer was washed with
saturated brine and dried over MgSO4. After filtration, the solvent was
removed in a rotary evaporator (40–45 C). The crude product was
subjected to column chromatography (SiO2; eluent, hexane/ CH2Cl2,
3:1) to give the corresponding compounds.
N,N-dimethyl-4-(phenylethynyl)aniline (2a): Pale yellow powder;
yield 88; m.p. 107–109°C (lit.26 109–110°C). 1H NMR (500 MHz,
CDCl3): δ 2.97(s, 6H), 6.65(d, J = 9.0 Hz, 2H), 7.25-7.32(m, 3H),
7.40(d, J = 9.0 Hz, 2H), 7.49(d, J = 9.0 Hz, 2H). 13C NMR (125 MHz,
CDCl3): δ 40.2, 87.3, 90.6, 110.1, 111.9, 124.2, 127.4, 128.2, 131.3,
132.7, 150.1. Anal. calcd for C16H15N: C, 86.84; H, 6.83; N, 6.33; found:
C, 86.56; H, 6.85; N, 6.27%.
Dimethylamino-substituted arylene-ethynylenes 1a–c and
2a–c were synthesised by Sonogashira coupling reactions.
Spectroscopic studies and theoretical calculations were
performed. The spectroscopic properties of arylene-ethynylenes
depend on the position of dimethylamino group. Arylene-
ethynylenes with a dimethylamino group present in the ortho-
position show the shortest wavelength absorption maxima, the
largest Stokes shift and the highest fluorescence efficiency.
Notably, a particularly large Stokes shift (151 nm) of 2c was
observed with a limited conjugation extent of two benzene rings.
o
The authors acknowledge financial assistance from the Natural
Science Foundation of Jiangsu Province under grant no.
BK20140780.
Received 13 May 2015; accepted 27 July 2015
Paper 1503361 doi: 10.3184/174751915X14383380888501
Published online: 7 August 2015
N,N-Dimethyl-3-(phenylethynyl)aniline (2b): Pale yellow powder;
yield 92%; m.p. 70–71°C. 1H NMR (500 MHz, CDCl3): δ 2.95(s, 6H),

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