Synthesis and photophysical properties of novel fluorescent quinoline-based aryl substituted styryl systems

Article abstract of DOI:10.3184/030823410X12780936189898

Synthesis of (E)-2-(4-bromostyryl)quinoline has been easily achieved by an acid catalysed condensation of 2-methylquinoline with 4-bromobenzaldehyde. Various boronic acid derivatives reacted with (E)-2-(4-bromostyryl)quinoline to afford a series of novel

Full text of DOI:10.3184/030823410X12780936189898

JOURNAL OF CHEMICAL RESEARCH 2010
RESEARCH PAPER 379
JULY, 379–381
Synthesis and photophysical properties of novel fluorescent
quinoline-based aryl substituted styryl systems
Qian Li, Bao Li, Bin Liu and Mingxin Yu*
Department of Chemistry, Zhejiang University, Hangzhou 310027, P. R. China
Synthesis of (E)-2-(4-bromostyryl)quinoline has been easily achieved by an acid catalysed condensation of
2-methylquinoline with 4-bromobenzaldehyde. Various boronic acid derivatives reacted with (E)-2-(4-
bromostyryl)quinoline to afford a series of novel quinoline-based aryl substituted styryl derivatives by the catalysis
of Pd(PPh3)4 at 85 °C in dimethoxyethane. The UV-Vis absorption and photoluminescent spectra of them in CH2Cl2
were investigated.
Keywords: quinoline, styryl systems, biaryl units, aryl bromide, Pd-catalysed
The emerging field of organic light-emitting diodes (OLEDs)1
is attracting considerable interest owing their technological
promise for the development of next generation low cost
full-colour displays and emissive products.2–4 Among OLED
materials, the use of organic conjugated materials as active
elements in light-emitting displays, envisioned nearly two
decades ago, has now reached the stage of commercialisation.5
For material research, quinoline as fluorescent compounds of
high quantum yield is an electron-deficient system with good
thermal stability, comparatively easy to prepare and has excel-
lent electroluminescent properties when the quinoline is
suitability substituted at the right positions.6,7 Biaryl units and
quinoline ring system8 as versatile intermediates in organic
synthesis and essential structural fragment of a large number
of natural and unnatural compounds possessing a wide range
of pharmacological and biological activity,9,10 in addition to
their application in materials science.
devices. We now report the design and synthesis of several
novel fluorescent quinoline-based aryl substituted styryl
derivatives via palladium-catalysed coupling.
The target compounds (2a–g) were obtained by a two-step
procedure. (see Scheme 1). The synthesis of (E)-2-(4-
bromostyryl)quinoline has been reported in our previous
work.15 It was an acid catalysed condensation of 2-methylquin-
oline and 4-bromobenzaldehyde. For the second step, various
boronic acid derivatives reacted with the (E)-2-(4-bromosty-
ryl) quinoline to afford quinoline-based aryl substituted styryl
compounds by the catalysis of Pd(PPh3)4 at 85 °C in dime-
thoxyethane. The E/Z isomerisation proportions of target
compounds are between 98/2 and 91/9. This reaction may be a
photoreversible process.16 The yields, isomerisation propor-
tions of the products as well as the reaction time were shown
in Table 1.
In order to investigate the photophysical properties of the
quinoline-based aryl substituted styryl derivatives, the UV and
PL spectra (Table 2) in dilute dichloromethane solution were
recorded. Most of them displayed two absorption peaks in
We have previously shown the preparation of a series of
novel, functionalised arylamine and acrylonitrile4,11–14 deriva-
tives as promising compounds for application in electronic
Scheme 1
* Correspondent. E-mail: mingxinyu@zju.edu.cn

380 JOURNAL OF CHEMICAL RESEARCH 2010
Table 1 Structures, reaction conditions and yields of novel
solution was poured into 10% sodium hydroxide solution (50 mL).
After the oil congealed, the solid was removed by filtration, washed
with water and then with ice cold ethanol (10 mL) and dried at
60 °C. 60–70% yield. White solid, yield: 68%. M.p. 133–134 °C.
(lit.15 133–134 °C), FTIR (KEr pellet, cm−1): 3045, 1588, 1498, 1395,
1062, 1005, 965, 821, 745. 1H NMR(400 MHz, CDCl3) δH: 8.11
(d, J = 8.8 Hz,1 H), 8.07 (d, J = 8.4, 1 H), 7.77 (d, J = 8.8 Hz, 1 H),
7.70 (dd, J = 7.6 Hz, J = 8.0 Hz, 1 H), 7.63 (d, J = 3.6 Hz, 1 H), 7.60
(d, J = 4.0 Hz 1 H); 7.50 (m, 5 H), 7.37 (d, J = 16 Hz 1 H). l3C NMR
(400 MHz, CDCl3) δc: 155.5, 148.2, 136.5, 135.5, 133.1, 131.9, 129.9,
129.6, 129.2, 128.7, 127.5, 127.4, 126.3, 122.5, 119.3.
compounds
Entry
R1
R2
R3
Time/h
E/Z
Yields/%
2a
2b
2c
2d
2e
2f
H
H
H
H
H
CH3
OCH3
Cl
5
8
5
6
5
5
7
95/5
95/5
93/7
91/9
96/4
93/7
98/2
90
85
87
80
83
77
84
H
H
H
H
CH3
—
—
CH3
—
—
H
—
—
2g
Synthesis of novel conjugated quinoline derivatives; general
procedure
Table 2 Photophysical properties of compounds 2a–g
To a 25 mL sidearm flask was added compound 1 (1.00 mmol),
boronic acid derivatives (1.10 mmol), Pd(PPh3)4 (0.012 mmol) and
sodium carbonate (0.233 g, 2.20 mmol). Water (2.0 mL), EtOH
(3.0 mL), dimethoxyethane (7.5 mL) was injected into the flask from
a syringe. The reaction mixture was heated and stirred at 85 °C under
nitrogen for an appropriate time until the reaction was complete. The
reaction mixture was then cooled to room temperature, filtered through
a mixture of celite and silica gel pad and washed with dichlorometh-
ane. The filtrate was washed with water and then dried by MgS04.
Concentration of the filtrate on a rotary evaporator followed by
washing of the solid material with ice cold ethanol afforded the
desired crude product. The crude product was purified by column
chromatography on silica gel using ethyl acetate/hexane (1:10) as
eluents.
Entry
aλmaxabs/nm
bλmaxem/nm
2a
2b
2c
2d
2e
2f
306, 361
302, 355
304, 370
307, 358
304, 357
293, 356
295, 368
409
418
442
405
414
430
423
2g
a Maximum absorption wavelength in CH2Cl2.
b Maximum emission wavelength in CH2Cl2.
(E)-2-[2-([1,1p-biphenyl]-4-yl)vinyl]quinoline (2a):17 Pale yellow
solid, yield: 90%. M.p. 192–193 °C [lit.17 186 °C(C6H6)]. FT-IR (KBr
pellet, cm−1): 3017, 2363, 1655, 1637, 1558, 1510, 1384, 830, 765,
693. 1H NMR (400 MHz, CDCl3) δH: 8.12(d, J = 8.8 Hz, 1 H), 8.09 (d,
J = 8.4 Hz, 1 H), 7.78(d, J = 8.4 Hz,1 H), 7.74–7.67 (m, 5 H), 7.65–
7.62 (m, 4 H), 7.50 (d, J = 7.6 Hz, 1 H). 7.47–7.43 (m, 3 H), 7.35 (dd,
J = 7.6 Hz , J = 6.8 Hz ,1 H). 13C NMR (400 MHz, CDCl3) δc: 157.00,
148.17, 141.34, 140.46, 136.41, 135.47, 134.06, 130.86, 129.67,
129.52, 129.15, 128.83, 127.73, 127.51, 126.91, 126.44, 126.20,
122.23, 119.29. MS m/z: 307 (M+).
the UV spectra at about 293–307 nm which were ascribed to
the absorption in a π–π* transition of the compounds and 355–
370 nm assigned to the absorbing transition of intermolecular
electron transfer. As Table 2 shows, when R3 was electron
donating group (methoxy) (2c), the absorption maximum
was redshifted by 12 nm compared to when R3 was electron-
withdrawing group (chlorine) (2d), which showed that
there was obvious electron transfer with the change of the
substituent group in conjugated system.
(E)-2-[2-(4p-methyl-[1,1p-biphenyl]-4-yl)vinyl]quinoline (2b): Pale
yellow solid, yield: 85%. M.p. 226–227 °C. FT-IR (KBr pellet, cm−1):
3019, 2917, 2360, 1648, 1623, 1558, 1507, 1384, 872, 824. 1H NMR
(400 MHz, CDCl3) δH: 8.16–8.10 (m, 2 H), 7.80 (d, J = 8.0 Hz, 1 H),
7.76–7.69 (m, 5 H), 7.65 (d, J = 8.4 Hz, 2 H), 7.56 (d, J = 8.0 Hz,
2 H), 7.54–7.44 (m, 2 H), 7.29–7.24 (m, 2 H), 2.42 (s, 3 H). 13C NMR
(400 MHz, CDCl3) δc: 155.99, 148.18, 141.28, 140.51, 137.35, 136.35,
135.21, 134.06, 130.72, 129.51, 129.15, 128.72, 127.69, 127.48,
127.21, 126.64, 126.15, 122.24, 119.27, 21.11. MS m/z: 321 (M+).
Anal. Calcd for C24H19N: C, 89.68; H, 5.96; N, 4.36. Found: C, 89.37;
H, 5.87; N, 4.32%.
The emission peaks of compounds were located at about
405–442 nm. The emission peak of 2c was redshifted by 37 nm
compared to the compound of 2d. All compounds yield blue
emissions in CH2Cl2 solution at room temperature.
Conclusion
In conclusion, several novel quinoline-based aryl substituted
styryl derivatives have been synthesised. This methodology
requires mild conditions and employs very simple starting
materials and inexpensive and easily handled catalysts. The
absorption and photoluminescent spectra of these derivatives
in CH2Cl2 were investigated. These compounds exhibit similar
absorption and emission behaviour and emit strongly in solu-
tion, with the emission maxima in the range of 405–442 nm.
(E)-2-[2-(4p-methoxy-[1,1p-biphenyl]-4-yl)vinyl]quinoline
(2c):
Pale yellow solid, yield: 87%. M.p. 209–210 °C. FT-IR (KBr pellet,
cm−1): 3017, 2913, 2360, 1654, 1625, 1558, 1507, 1384, 872, 824. 1H
NMR (400 MHz, CDCl3) δH: 8.16 (d, J = 8.8 Hz, 1 H), 8.12 (d, J = 8.4
Hz, 1 H), 7.81 (d, J = 8.0 Hz, 1 H), 7.76–7.71 (m, 5 H), 7.61 (dd,
J = 9.2 Hz, J = 8.4 Hz, 4 H), 7.56–7.44 (m, 2 H), 7.02–6.97 (m, 2 H).
3.88 (s,3 H). 13C NMR (400 MHz, CDCl3) δc: 156.02, 148.18, 140.96,
140.18, 136.36, 134.87, 134.10, 132.96, 130.62, 129.65, 129.10,
128.55, 127.98, 127.72, 127.48, 126.93, 126.37, 119.26, 114.27,
55.17. MS m/z: 337 (M+). Anal. Calcd for C24H19NO: C, 85.43; H,
5.68; N, 4.15. Found: C, 85.25; H, 5.59; N, 4.08%.
Experimental
The boronic acid derivatives, tetrakis(triphenylphosphine)palladium
were products of the Aldrich Chemical Co. Sodium carbonate was
purchased from Alfa-Aesar and stored in a Vacuum Atmospheres
glove box under nitrogen. Toluene was distilled under nitrogen from
molten sodium. All chemicals were used as supplied. All melting
points were determined with a WRS-1A melting point apparatus and
were uncorrected. NMR (1H NMR and l3C NMR) spectra were run on
a Bruker AV-400 NMR spectrometer in CDCl3 and chemical shifts
expressed as δ (ppm) values with TMS as an internal standard.
IR spectra were recorded in KBr on a Nicolet NEXUS 470 FT-IR
spectrophotometer. Vibrational transition frequencies are reported
in wave numbers (cm−1). Mass spectra were obtained on HP5989B
mass spectrometer. Elemental analysis was performed on a Perkin-
Elmer 240 analyser. UV-vis spectra were recorded on a Hitachi
U-3300 model while PL spectra were taken using a Hitachi F-4500
fluorescence spectrophotometer.
(E)-2-[2-(4p-chloro-[1,1p-biphenyl]-4-yl)vinyl]quinoline (2d): Pale
yellow solid, yield: 80%. M.p. 190–191 °C. FT-IR (KBr pellet, cm−1):
1
3023, 2360, 1657, 1631, 1558, 1507, 1384, 827, 758. H NMR (400
MHz, CDCl3) δH: 8.15 (d, J = 8.0 Hz, 1 H), 8.12 (d, J = 8.4 Hz, 1 H),
7.81 (d, J = 8.4 Hz, 1 H), 7.76–7.69 (m, 5 H), 7.63–7.49 (m, 5 H),
7.45–7.40 (m, 3 H). 13C NMR (400 MHz, CDCl3) δc: 155.83, 148.24,
139.92, 138.87, 136.36, 135.85, 133.71, 130.91, 129.79, 129.18,
128.98, 128.14, 127.79, 127.51, 127.24, 126.68, 126.22, 122.18,
119.31. MS m/z: 341 (M+). Anal. Calcd for C23H16ClN: C, 80.81; H,
4.72; N, 4.10. Found: C, 80.31; H, 4.68; N, 3.95%.
(E)-2-[2-(3p,5p-dimethyl-[1,1p-biphenyl]-4-yl)vinyl]quinoline (2e):
Pale yellow solid, yield: 83%. M.p. 142–143 °C. FT-IR (KBr pellet,
cm−1): 3017, 2913, 2360, 1637, 1597, 1560, 1501, 1384, 830, 752.
1H NMR (400 MHz, CDCl3) δH: 8.11 (dd, J = 8.4 Hz, J = 8.4 Hz, 2 H),
7.78 (d, J = 8.0 Hz, 1 H), 7.74–7.67 (m, 5 H), 7.63 (d, J = 8.4 Hz,
2 H), 7.52–7.43 (m, 2 H), 7.26 (s, 2 H), 7.02 (1 H), 2.40 (s, 6 H).
13C NMR (400 MHz, CDCl3) δc: 156.01, 148.22, 141.59, 140.46,
138.33, 136.35, 135.32, 134.07, 129.77, 129.18, 129.14, 128.76,
(E)-2-(4-bromostyryl)quinoline (1):15 A solution of 2-methyquino-
line 10.5 g (0.0734 mol), 4-bromobenzaldehyde (0.084 mol) and 5 g
(0.0375 mol) of acetic anhydride was heated at 150 °C for 16 h in a
50 mL round bottomed flask fitted with a reflux condenser. The hot

JOURNAL OF CHEMICAL RESEARCH 2010 381
127.63, 127.51, 127.47, 127.31, 126.16, 124.89, 119.25, 21.42. MS
m/z: 335 (M+). Anal. Calcd for C25H21N: C, 89.51; H, 6.31; N, 4.18.
Found: C, 89.29; H, 6.18; N, 4.03%.
Received 19 April 2010; accepted 7 June 2010
Paper 1000081 doi: 10.3184/030823410X12780936189898
Published online: 28 July 2010
(E)-2-[4-(naphthalen-1-yl)styryl]quinoline (2f): Pale yellow solid,
yield: 77%. M.p. 148–149 °C. FT-IR (KBr pellet, cm−1): 3028, 2359,
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The project is sponsored by the Natural Science Foundation
for the Education Ministry of Zhejiang Province
(Y200908302).

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