Synthesis and optical behaviors of 2-(9-phenanthrenyl)-, 2-(9-anthryl)-, and 2-(1-pyrenyl)-1-alkylimidazole homologues

Article abstract of DOI:10.1016/j.saa.2009.06.020

Eight 2-(9-phenanthrenyl)-, 2-(9-anthryl)- and 2-(1-pyrenyl)-1-alkyl-benzimidazole compounds, three 2-(9-anthryl)-1-alkylphenanthroimidazole compounds and five 4,5-diphenyl-1-alkyl-2-(9-anthryl)imidazole compounds were synthesized by alkylation reactions

Full text of DOI:10.1016/j.saa.2009.06.020

Spectrochimica Acta Part A 74 (2009) 233–242
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and optical behaviors of 2-(9-phenanthrenyl)-, 2-(9-anthryl)-, and
2-(1-pyrenyl)-1-alkylimidazole homologues
Yun-Nan Yana, Dan-Yan Lina, Wen-Long Panb, Xiu-Ling Lia, Yi-Qian Wana,
Yu-Liang Maic, Hua-Can Songa,∗
a School of Chemistry and Chemical Engineering, Sun Yat-Sen University, Guangzhou 510275, PR China
b China National Analysis Center, Guangzhou 510070, PR China
c Guangdong Public Laboratory of Chemical Engineering, Guangdong Petrochemical Industry Research Institute, Guangzhou 510665, PR China
a r t i c l e i n f o
a b s t r a c t
Article history:
Eight 2-(9-phenanthrenyl)-, 2-(9-anthryl)- and 2-(1-pyrenyl)-1-alkyl-benzimidazole compounds,
three 2-(9-anthryl)-1-alkylphenanthroimidazole compounds and five 4,5-diphenyl-1-alkyl-2-(9-
anthryl)imidazole compounds were synthesized by alkylation reactions of the corresponding benzim-
idazole, phenanthroimidazole or imidazole compounds. 2-(10-Bromo-9-anthryl)-1-alkyl-benzimidazole
compounds were prepared by bromination reaction of 2-(9-anthryl)-1-alkylbenzimidazole compounds.
All the synthesized compounds were characterized by elemental analysis, 1H NMR, 13 C NMR, MS or HRMS;
theirabsorption coefficients (ε), maximum absorption ꢀamax, fluorescence emissionmaximum ꢀem, Stokes
shifts and fluorescence quantum yields (˚F) in ethyl acetate were determined; their fluorescent lifetimes
(T1 and T2) were measured in ethyl acetate and in solid state, respectively. The crystal structure of 2-(9-
anthryl)-1-n-butyl-4,5-diphenylimidazole (12a) was determined to be triclinic, space group P-1 types,
using single crystal X-ray crystallography technique. The results showed that these compounds exhibited
moderate fluorescence-emission abilities and higher solubility in most organic solvents than their cor-
responding starting materials. The relationships between the optical behaviors and structures for these
compounds were discussed.
Received 16 November 2008
Received in revised form 6 June 2009
Accepted 7 June 2009
Keywords:
2-Arylbenzimidazole homologues
Synthesis
Absorption spectra
Emission spectra
Quantum yields
Fluorescence lifetime
© 2009 Published by Elsevier B.V.
1. Introduction
alkylate those compounds because they could not be used in many
fields due to their low solubility in most organic solvents. On
It has attracted a tremendous amount of recent attention to
synthesize and investigate the compounds containing a large
conjugated-system, because these compounds could be used as
organic optical materials in many fields, for example as organic
light-emitting device (OLED) materials [1–8], two-photon absorp-
tion materials [9–12], three-dimensional optical data storage
[13,14], treating cancer with optical dynamics [15], two-photon
fluorescent microscopy and imaging [16], two-photon frequency
up-converted lasing, optical power limiting [17] and nonlinear
optical and photorefractive applications [18–21]. There are several
reports about the synthesis, optical behaviors and uses of 2-
(9-anthryl)-, 2-(9-phenanthrenyl)- or 2-(1-pyrenyl)benzimidazole
compounds, 2-(9-anthryl)phenanthroimidazole compounds and
4,5-diphenyl-2-(9-anthryl)imidazole compounds [22–32]. How-
ever, there are a few reports about the alkylation of these
compounds to our best knowledge. Meantime, it is necessary to
the other hand, it could be a more puzzling problem to alkylate
these compounds because they could not be alkylated by ordinary
method using sodium, potassium or sodium hydride as depro-
tonating agent due to their lower solubility in organic solvents
and the steric hindrance in these molecules, especially in 2-(9-
anthryl)phenanthroimidazole. Finally, the alkyl group to 1-position
of imidazole would affect the molecular planarity, which is very
important for the optical behaviors of organic compounds, since
the imidazole or benzimidazole moiety can turn around the aryl on
2-position of imidazole. The information mentioned above encour-
aged us to investigate the alkylation reaction of these imidazole
or bezimidazole compound. Based on our previous works [33–37]
a series of corresponding alkylated compound were obtained, and
their absorption coefficients (ε), maximum absorption ꢀamax, flu-
orescence emission maximum ꢀem, Stokes shifts, quantum yields
(˚F) and fluorescent lifetime (T1 and T2) values in ethyl acetate
were determined. In order to compare their spectral behaviors in
solution and in solid state, the ꢀamax, ꢀem, T1, T2 values of some
samples in solid state were determined. The synthetic route and
structures are shown in Fig. 1.
∗
Corresponding author. Tel.: +86 20 84110918; fax: +86 20 84112245.
E-mail address: yjhxhc@mail.sysu.edu.cn (H.-C. Song).
1386-1425/$ – see front matter © 2009 Published by Elsevier B.V.
doi:10.1016/j.saa.2009.06.020

234
Y.-N. Yan et al. / Spectrochimica Acta Part A 74 (2009) 233–242
Fig. 1. The synthetic route and structures.
2. Experimental
ter. Fluorescence Lifetime values were determined on EDINBURGH
FLSP920. Thermogravimetric analysis (TGA) was carried out up to
700 ◦C with a heating speed of 10.0 K/min in nitrogen atmosphere
on a Netzsch TG-209 thermogravimetric analyzer. All the chemi-
cals are commercial available and they were used without further
purification. All the solvents were dried using standard methods
before use.
2.1. Reagents and instruments
All melting points were determined on an X4 melting point
microscope. 1H NMR and 13C NMR spectra were run on a Bruker
AVANCE-300 NMR spectrometer. Mass spectra were taken with a
SHIMADZU LCMS-2010A. High-resolution mass spectra were mea-
sured on a Thermo MAT-95XP spectrometer. Element analysis was
taken with an Elementar Analysensysteme GmbH Vario EL. Single
crystal was characterized by Bruker Smart 1000 CCD X-ray single
crystal diffractometer. Ultraviolet spectra were recorded on a SHI-
MADZU UV-1601 spectrophotometer. Fluorescence spectra were
taken with a SHIMADZU RF-5301PC fluorescence spectrophotome-
2.2. Synthesis
2.2.1. Synthesis of benzimidazole or imidazole compounds
The starting materials for the synthesis of 3b is 3-(9-
anthryl)acrylic acid which was prepared according to references
[38,39].

Y.-N. Yan et al. / Spectrochimica Acta Part A 74 (2009) 233–242
235
2-(9-Anthryl)benzimidazole
(1a)
and
2-(1-
2.2.2.4. 2-(pyren-1-yl)-1-n-butylbenzimidazole (2d). Compound 2d
was obtained from 0.79 g (2.5 mmol) of 1b as yellow solids in 40%
yield. m.p. 153–154 ◦C. 1H NMR (CDCl3): 0.61 (t, J = 7.2 Hz, 3H, CH3),
0.79–0.80 (m, 2H, CH2), 0.90–1.08 (m, 2H, CH2), 4.07 (t, J = 7.2 Hz,
2H, NCH2), 7.37–7.39 (m, 2H, ArH), 7.49–7.52 (m, 1H, ArH), 7.94 (d,
J = 8.1 Hz, 2H, ArH), 8.05 (t, J = 8.4 Hz, 2H, ArH), 8.15 (t, J = 9.0 Hz, 3H,
ArH), 8.27 (t, J = 8.4 Hz, 3H, ArH). 13C NMR (CDCl3): 13.4, 19.7, 31.6,
44.4, 110.0, 120.0, 122.2, 122.6, 124.3, 124.4, 124.5, 124.9, 125.5,
125.7, 126.2, 127.1, 127.7, 128.4, 128.6, 130.3, 130.6, 131.0, 132.1,
135.0, 143.4, 152.9. Elemental analysis found (%) C, 85.80; H, 6.01;
N, 7.27; calculated for C27H22N2·0.2H2O: C, 85.77; H, 5.97; N, 7.41.
ESI-MS (m/z): 375 [M+H]+.
pyrenyl)benzimidazole (1b) were synthesized as described
[40], 2-(3-(2-hydroxynaphthalenyl))benzimidazole (3a) and 2-
(9-phenanthrenyl)benzimidazole (5) were respectively prepared
according to references [41,25]. 2-(9-Anthryl)phenanthroimidazole
(9) and 2-(9-anthryl)-4,5-diphenylimidazole (11) were prepared
according to reference [28].
2-(2-(9-Anthryl)-1-phenoxyvinyl)benzimidazole (7) A solution
of 2-(phenoxy- methyl)benzimidazole (0.22 g, 1 mmol) and 9-
anthrylcarbaldehyde (0.45 g, 1.2 mmol) in acetic anhydride (10 mL)
was refluxed for 18 h. After being cooled, the mixture was poured
into water. The resulting solids were filtrated off and recrystallized
from ethanol to give yellow solids, yield 40%, m.p. 184–186 ◦C. 1H
NMR (DMSO-d6): 7.54 (d, J = 8.0 Hz, 4H), 7.65 (d, J = 8.0 Hz, 4H), 8.20
(d, J = 8.4 Hz, 4H), 8.60 (d, J = 8.9 Hz, 4H), 8.73 (s, 2H), 9.09 (s, 1H).
13C NMR (DMSO-d6): 87.5, 125.1, 125.9, 126.2, 128.0, 130.0, 130.1,
131.4, 131.8, 169.8.
2.2.2.5. 2-(2(3-Butoxynaphthalenyl))-1-n-butylbenzimidazole (4).
Compound 4 was obtained from 0.65 g (2.5 mmol) of 3a as gray
solids in 43% yield. m.p. 96–97 ◦C. 1H NMR (DMSO-d6): 0.66 (t,
J = 7.2 Hz, 3H, CH3), 0.81 (t, J = 7.2 Hz, 3H, CH3), 1.02–1.15 (m, 2H,
CH2), 1.22–1.34 (m, 2H, CH2), 1.59–1.70 (m, 4H, CH2), 4.19 (t,
J = 6.6 Hz, 2H, NCH2), 4.34 (t, J = 6.9 Hz, 2H, OCH2), 7.50 (t, J = 7.5 Hz,
1H, ArH), 7.57–7.60 (m, 2H, ArH), 7.66 (t, J = 7.5 Hz, 1H, ArH), 7.70
(s, 1H, ArH), 7.84–7.87 (m, 1H, ArH), 7.97 (d, J = 7.8 Hz, 2H, ArH),
8.03–8.05 (m, 1H, ArH), 8.35 (s, 1H, ArH). 13C NMR (CDCl3): 13.3,
13.7, 19.1, 19.6, 30.8, 30.9, 45.8, 68.7, 107.7, 111.5, 113.5, 116.6, 124.9,
125.7, 125.8, 126.5, 127.7, 128.7, 128.9, 131.8, 132.7, 133.4, 133.5,
133.6, 133.7, 133.8, 136.2, 147.7, 152.9. Elemental analysis found
(%) C, 79.69; H, 7.58; N, 7.18; calculated for C25H28N2O·0.2H2O: C,
79.84; H, 7.61; N, 7.45. ESI-MS (m/z): 373 [M+H]+.
2.2.2. Alkylation reaction of benzimidazole or imidazole
compounds
General procedure:
A mixture of 2.5 mmol of imidazole
compound, 3.5 mmol of alkyl bromide, 0.25 g of tetra-n-
butylammonium bromide (TBAB), 8 mL of 50% aqueous sodium
hydroxide solution and 10 mL of butanone was refluxed for
1.5–3.5 h and the reacting mixture was monitored by TLC. After
butanone was evaporated under reduced pressure, the residue was
poured into 100 mL of water, the resulting solids were filtrated off
and the crude product was purified by chromatography on a silica
gel column to give the corresponding pure product.
2.2.2.6. 2-(9-Phenanthrenyl)-1-n-butylbenzimidazole
(6a). Com-
pound 6a was obtained from 0.73 g (2.5 mmol) of 5 as yellow solids
in 45% yield. m.p. 92–94 ◦C. 1H NMR (CDCl3): 0.68 (t, J = 7.2 Hz,
3H, CH3), 1.05–1.17 (m, 2H, CH2), 1.62–1.72 (m, 2H, CH2), 4.08
(t, J = 7.2 Hz, 2H, NCH2), 7.42–7.44 (m, 2H, ArH), 7.53–7.62 (m,
3H, ArH), 7.66–7.81 (m, 3H, ArH), 7.96–8.03 (m, 3H, ArH), 8.79
(t, J = 8.1 Hz, 2H, ArH). 13C NMR (CDCl3): 13.5, 19.8, 31.7, 44.5,
110.1, 120.2, 122.2, 122.5, 122.6, 122.8, 126.1, 126.9, 127.1, 127.4,
127.7, 129.0, 130.0, 130.3, 130.5, 130.6, 130.8, 134.8, 143.1, 152.3.
Elemental analysis found (%) C, 84.23; H, 6.78; N, 7.35; calculated
for C25H22N2·0.28H2O: C, 84.46; H, 6.40; N, 7.88. ESI-MS (m/z): 351
[M+H]+.
2.2.2.1. 2-(9-Anthryl)-1-n-butylbenzimidazole (2a). Compound 2a
was obtained from 0.73 g (2.5 mmol) of 1a as yellow solids in 54%
yield. m.p. 177–179 ◦C. 1H NMR (CDCl3): 0.52 (t, J = 7.2 Hz, 3H, CH3),
0.92–1.04 (m, 2H, CH2), 1.43–1.53 (m, 2H, CH2), 3.86 (t, J = 7.2 Hz, 2H,
NCH2), 7.42–7.51 (m, 8H, ArH), 7.57 (s, 1H, ArH), 8.12 (d, J = 7.8 Hz,
3H, ArH), 8.68 (s, 1H, ArH). 13C NMR (CDCl3): 13.2, 19.8, 31.7, 44.3,
109.9, 120.2, 122.1, 122.6, 124.1, 125.3, 125.4, 126.7, 128.4, 129.2,
130.9, 131.4, 134.9, 143.5, 151.0. Elemental analysis found (%) C,
83.73; H, 6.42; N, 7.38; calculated for C25H22N2·0.4H2O: C, 83.95;
H, 6.43; N, 7.83. HRMS (EI) (M+): Calcd. for C25H22N2: 350.1783;
Found: 350.1779.
2.2.2.7. 2-(9-Phenanthrenyl)-1-iso-butylbenzimidazole (6b). Com-
pound 6b was obtained from 0.73 g (2.5 mmol) of 5 as yellow solids
in yield 43%. m.p. 110–112 ◦C. 1H NMR (CDCl3): 0.67 (d, J = 6.0 Hz,
6H, CH3), 1.92–1.95 (m, 1H, CH), 3.90 (d, J = 6.9 Hz, 2H, NCH2),
7.34–7.39 (m, 2H, ArH), 7.48–7.56 (m, 2H, ArH), 7.61–7.79 (m, 4H,
ArH), 7.89–7.99 (m, 3H, ArH), 8.77 (t, J = 6.6 Hz, 2H, ArH). 13C NMR
(CDCl3): 19.9, 28.4, 52.0, 110.3, 120.4, 122.6, 122.8, 123.0, 123.2,
126.5, 127.3, 127.4, 127.5, 128.1, 129.4, 130.5, 130.6, 130.8, 130.9,
131.2, 135.1, 143.4, 152.6. Elemental analysis found (%) C, 85.52; H,
6.47; N, 7.92; calculated for C25H22N2: C, 85.68; H, 6.33; N, 7.99.
ESI-MS (m/z): 351 [M+H]+.
2.2.2.2. 2-(9-Anthryl)-1-iso-butylbenzimidazole (2b). Compound
2b was obtained from 0.73 g (2.5 mmol) of 1a as yellow solids in
45% yield. m.p. 144–146 ◦C. 1H NMR (CDCl3): 0.58 (d, J = 6.6 Hz, 6H,
CH3), 1.82–1.94 (m, 1H, CH), 3.70 (d, J = 7.5 Hz, 2H, NCH2), 7.39–7.59
(m, 9H, ArH), 7.95–7.98 (m, 1H, ArH), 8.10 (d, J = 8.4 Hz, 2H, ArH),
8.63 (s, 1H, ArH). 13C NMR (CDCl3): 20.1, 28.5, 52.1, 110.3, 120.1,
122.1, 122.6, 124.0, 125.3, 125.4, 126.7, 128.5, 129.3, 130.9, 131.3,
135.3, 143.4, 151.2. Elemental analysis found (%) C, 85.38; H, 6.37;
N 7.90; calculated for C25H22N2: C, 85.68; H, 6.33; N, 7.99. ESI-MS
(m/z): 351 [M+H]+.
2.2.2.8. 2-(9-Phenanthrenyl)-1-n-dedocylbenzimidazole (6c). Com-
pound 6c was obtained from 0.73 g (2.5 mmol) of 5 as oily liquid
in 48% yield. 1H NMR (CDCl3): 0.89 (t, J = 6.0 Hz, 3H, CH3), 1.13–1.27
(m, 18H, CH2), 1.51–1.61 (m, 2H, CH2), 4.05 (t, J = 6.3 Hz, 2H, NCH2),
7.37–7.39 (m, 2H, ArH), 7.48–7.57 (m, 2H, ArH), 7.66–7.81 (m, 4H,
ArH), 7.91–7.99 (m, 3H, ArH), 8.78 (t, J = 6.6 Hz, 2H, ArH). 13C NMR
(CDCl3): 14.6, 23.1, 26.2, 26.8, 29.2, 29.8, 29.9, 30.0, 32.3, 33.2, 44.9,
63.0, 110.4, 120.4, 122.6, 122.9, 123.0, 123.2, 126.5, 127.3, 127.4,
127.5, 128.1, 129.4, 130.5, 130.6, 130.8, 130.9, 131.2, 135.1, 143.4,
152.6. Elemental analysis found (%) C, 85.40; H, 8.30; N, 5.95; cal-
culated for C33H38N2: C, 85.67; H, 8.28; N, 6.05. ESI-MS (m/z): 463
[M+H]+.
2.2.2.3. 2-(9-Anthryl)-1-n-dedocylbenzimidazole (2c). Compound
2c was obtained from 0.73 g (2.5 mmol) of 1a as yellow solids in
50% yield. m.p. 66–68 ◦C. 1H NMR (CDCl3): 0.76–0.96 (m, 11H,
CH3, CH2), 1.10–1.33 (m, 10H, CH2), 1.44–1.54 (m, 2H, CH2), 3.82
(t, J = 7.2 Hz, 2H, NCH2), 7.39–7.56 (m, 9H, ArH), 7.95–7.98 (m, 1H,
ArH), 8.10 (d, J = 8.1 Hz, 2H, ArH), 8.64 (s, 1H, ArH). 13C NMR (CDCl3):
14.7, 23.2, 26.9, 29.1, 29.5, 29.8, 29.9, 30.0, 32.4, 45.0, 110.6, 120.8,
122.7, 123.2, 124.7, 126.0, 126.1, 127.4, 129.1, 129.9, 131.6, 132.0,
135.5, 144.2, 151.7. Elemental analysis found (%) C, 85.42; H, 8.32;
N, 5.91; calculated for C33H38N2: C, 85.67; H, 8.28; N, 6.05. ESI-MS
(m/z): 463 [M+H]+.

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Y.-N. Yan et al. / Spectrochimica Acta Part A 74 (2009) 233–242
2.2.2.9. 2-(9-Anthryl)-1-n-butylphenanthroimidazole (10a). Com-
pound 10a was obtained from 0.99 g (2.5 mmol) of 9 as yellow
solids in 60% yield. m.p. 236–238 ◦C. 1H NMR (CDCl3): 0.43 (t,
J = 7.5 Hz, 3H, CH3), 0.89–1.01 (m, 2H, CH2), 1.61–1.71 (m, 2H, CH2),
4.12 (t, J = 7.5 Hz, 2H, NCH2), 7.17 (s, 1H, ArH), 7.34 (t, J = 7.5 Hz, 2H,
ArH), 7.42 (t, J = 7.5 Hz, 2H, ArH), 7.54–7.62 (m, 5H, ArH), 8.04 (d,
J = 7.8 Hz, 2H, ArH), 8.24 (d, J = 6.9 Hz, 1H, ArH), 8.59 (d, J = 7.5 Hz,
1H, ArH), 8.70 (d, J = 7.5 Hz, 1H, ArH), 8.77 (d, J = 6.6 Hz, 1H, ArH),
8.85 (d, J = 7.5 Hz, 1H, ArH). 13C NMR (CDCl3): 13.7, 20.1, 32.7, 47.2,
121.3, 123.3, 123.6, 124.0, 125.0, 125.4, 126.0, 126.1, 126.3, 127.3,
127.4, 127.9, 128.6, 129.1, 129.7, 130.0, 131.8, 132.8, 139.0, 149.8.
Elemental analysis found (%) C, 86.65; H, 6.52; N, 5.44; calculated
for C33H26N2·0.45H2O: C, 86.41; H, 5.91; N, 6.11. HRMS (EI) (M+):
Calcd. for C33H26N2: 450.2096; Found: 450.2090.
137.8, 144.3. Elemental analysis found (%) C, 87.00; H, 6.58; N, 5.92;
calculated for C34H30N2·0.2H2O: C, 86.85; H, 6.52; N, 5.96. ESI-MS
(m/z): 468 [M+H]+.
2.2.2.14. 2-(9-Anthryl)-1-n-dodecyl-4,5-diphenylimidazole
(12c).
Compound 12c was obtained from 0.99 g (2.5 mmol) of 11 as
yellow solids in 51% yield. m.p. 129–130 ◦C. 1H NMR (CDCl3):
0.48–0.74 (m, 6H, CH2), 0.81–0.94 (m, 5H, CH3, CH2), 0.94–1.40
(m, 12H, CH2), 3.46 (t, J = 7.5 Hz, 2H, NCH2), 7.10–7.23 (m, 3H,
ArH), 7.41–7.56 (m, 9H, ArH), 7.65 (d, J = 7.2 Hz, 2H, ArH), 7.76–7.81
(m, 2H, ArH), 8.01–8.06 (m, 2H, ArH), 8.56 (s, 1H, ArH). 13C NMR
(CDCl3): 14.2, 22.8, 26.0, 28.3, 28.9, 29.3, 29.4, 29.5, 29.6, 30.2,
31.9, 44.7, 125.1, 125.3, 125.9, 126.1, 126.5, 126.7, 127.9, 128.4,
128.5, 128.8, 129.0, 129.1, 131.0, 131.2, 131.7, 131.9, 134.7, 137.8,
144.3. Elemental analysis found (%) C, 87.15; H, 7.96; N, 4.87;
calculated for C41H44N2: C, 87.19; H, 7.85; N, 4.96. ESI-MS (m/z):
566 [M+H]+.
2.2.2.10. 2-(9-Anthryl)-1-iso-butylphenanthroimidazole
(10b).
Compound 10b was obtained from 0.99 g (2.5 mmol) of 9 as yellow
solids in 45% yield. m.p. 266–268 ◦C. 1H NMR (CDCl3): 0.58 (d,
J = 6.6 Hz, 6H, CH3), 2.29–2.43 (m, 1H, CH), 4.12 (d, J = 6.9 Hz, 2H,
NCH2), 7.42–7.56 (m, 4H, ArH), 7.65–7.74 (m, 4H, ArH), 7.86 (d,
J = 8.4 Hz, 2H, ArH), 8.13 (d, J = 8.1 Hz, 2H, ArH), 8.32 (d, J = 8.1 Hz, 1H,
ArH), 8.67 (s, 1H, ArH), 8.79 (d, J = 7.2 Hz, 1H, ArH), 8.88 (d, J = 7.5 Hz,
1H, ArH), 8.94 (d, J = 7.5 Hz, 1H, ArH). 13C NMR (CDCl3): 20.3, 28.7,
54.9, 121.7, 123.3, 123.6, 125.0, 125.3, 126.9, 126.1, 126.6, 127.1,
127.4, 127.8, 128.7, 129.2, 129.8, 130.1, 131.8, 132.5, 139.1, 150.2.
Elemental analysis found (%) C, 87.20; H, 6.21; N, 6.08; calculated
for C33H26N2·0.25H2O: C, 87.10; H, 5.87; N, 6.16. ESI-MS (m/z): 451
[M+H]+.
2.2.3. Bromination of compound 12 into compound 13
General procedure: Compound 12 (1 mmol) was dissolved in CS2
(20 mL) and then treated with bromine (0.18 g; 1.1 mmol) in CS2
(5 mL). After being stirred for 3 h at room temperature the solvent
was evaporated under reduced pressure, and the residues were
recrystallized from ethanol to give 13 as yellow solids.
2.2.3.1. 2-(9(10-Bromoanthryl))-1-n-butyl-4,5-diphenylimidazole
(13a). Compound 13a was obtained from 0.45 g (1 mmol) of 12a as
yellow solids in 65% yield. m.p. 175–177 ◦C. 1H NMR (CDCl3): 0.26
(t, J = 7.2 Hz, 3H, CH3), 0.62–0.74 (m, 2H, CH2), 0.94–1.05 (m, 2H,
CH2), 3.44 (t, J = 7.2 Hz, 2H, NCH2), 7.11–7.24 (m, 3H, ArH), 7.46–7.53
(m, 7H, ArH), 7.59–7.65 (m, 4H, ArH), 7.78 (d, J = 8.7 Hz, 2H, ArH),
8.62 (d, J = 8.7 Hz, 2H, ArH). 13C NMR (CDCl3): 12.9, 19.3, 32.4, 44.4,
125.4, 125.9, 126.2, 126.3, 126.6, 126.8, 127.1, 128.0, 128.6, 129.0,
129.2, 130.3, 131.0, 131.4, 132.5, 134.5, 137.9, 143.6. ESI-MS (m/z):
531 [M+H]+.
2.2.2.11. 2-(9-Anthryl)-1-n-dedocylphenanthroimidazole
(10c).
Compound 10c was obtained from 0.99 g (2.5 mmol) of 9 as yellow
solids in 50% yield. m.p. 92–94 ◦C. 1H NMR (CDCl3): 0.84–1.01 (m,
11H, CH3, CH2), 1.10–1.34 (m, 10H, CH2), 1.70–1.82 (m, 2H, CH2),
4.20 (t, J = 7.5 Hz, 2H, NCH2), 7.42 (t, J = 8.1 Hz, 2H, ArH), 7.48 (t,
J = 7.2 Hz, 2H, ArH), 7.64–7.74 (m, 6H, ArH), 8.13 (d, J = 8.7 Hz, 2H,
ArH), 8.32 (d, J = 8.7 Hz, 1H, ArH), 8.68 (s, 1H, ArH), 8.80 (d, J = 8.1 Hz,
1H, ArH), 8.86 (d, J = 7.2 Hz, 1H, ArH), 8.94 (d, J = 7.8 Hz, 1H, ArH).
13C NMR (CDCl3): 14.7, 23.2, 26.8, 29.0, 29.5, 29.8, 29.9, 30.0, 30.1,
30.5, 32.4, 47.4, 121.3, 123.3, 123.6, 124.0, 125.0, 125.4, 126.0, 126.1,
126.4, 127.3, 127.4, 127.9, 128.6, 129.1, 129.7, 130.0, 131.7, 132.8,
139.0, 142.6, 149.8. Elemental analysis found (%) C, 86.46; H, 8.02;
N, 4.98; calculated for C41H42N2·0.4H2O: C, 86.39; H, 7.57; N, 4.91.
ESI-MS (m/z): 563 [M+H]+.
2.2.3.2. 2-(9(10-Bromoanthryl))-1-n-dedocyl-4,5-diphenylimidazole
(13b). Compound 13b was obtained from 0.56 g (1 mmol) of 12c
as yellow solids in 64% yield. m.p. 109–111 ◦C. 1H NMR (CDCl3):
0.49–0.75 (m, 6H, CH2), 0.83–0.94 (m, 5H, CH3, CH2), 0.94–1.28
(m, 12H, CH2), 3.43 (t, J = 7.2 Hz, 2H, NCH2), 7.11–7.24 (m, 3H, ArH),
7.45–7.53 (m, 7H, ArH), 7.61 (t, J = 7.2 Hz, 4H), 7.78 (d, J = 8.7 Hz, 2H,
ArH), 8.62 (d, J = 8.7 Hz, 2H, ArH). 13C NMR (CDCl3): 14.2, 22.8, 25.9,
28.3, 28.9, 29.3, 29.4, 29.5, 29.6, 30.2, 31.9, 44.7, 125.4, 125.9, 126.2,
126.3, 126.6, 126.8, 127.1, 128.0, 128.6, 129.0, 129.2, 130.3, 131.0,
131.4, 132.5, 134.5, 137.9, 143.6. ESI-MS (m/z): 643 [M+H]+.
2.2.2.12. 2-(9-Anthryl)-1-n-butyl-4,5-diphenylimidazole
(12a).
Compound 12a was obtained from 0.99 g (2.5 mmol) of 11 as
yellow solids in 51% yield. m.p. 142–143 ◦C. 1H NMR (CDCl3): 0.23
(t, J = 7.2 Hz, 3H, CH3), 0.61–0.73 (m, 2H, CH2), 0.95–1.05 (m, 2H,
CH2), 3.47 (t, J = 7.5 Hz, 2H, NCH2), 7.10–7.23 (m, 3H, ArH), 7.41–7.56
(m, 9H, ArH), 7.65 (d, J = 6.9 Hz, 2H, ArH), 7.76–7.80 (m, 2H, ArH),
8.01–8.05 (m, 2H, ArH), 8.57 (s, 1H, ArH). 13C NMR (CDCl3): 12.9,
19.3, 32.4, 44.4, 125.1, 125.3, 125.8, 126.1, 126.5, 126.7, 127.9, 128.4,
128.5, 128.8, 129.0, 129.1, 131.0, 131.2, 131.6, 131.9, 134.7, 137.8,
144.3. Elemental analysis found (%) C, 86.38; H, 6.45; N, 6.10;
calculated for C34H32N2·0.4H2O: C, 86.20; H, 6.31; N, 6.09. ESI-MS
(m/z): 453 [M+H]+.
3. Results and discussion
3.1. Synthesis
3.1.1. Synthesis of benzimidazole or imidazole compounds
2-(9-Anthryl)benzimidazole
(1a)
and
2-(1-
pyrenyl)benzimidazole (1b) were prepared according to
references [24–27] by the condensation reaction of 9-
anthraldehyde and benzene-1,2-diamine in ethanol under
reflux; 2-(9-Phenanthrenyl)benzimidazole (5) and 2-(3-(2-
hydroxynaphthalenyl))benzimidazole (3a) were synthesized by
the reaction of phenanthrene-9-carbonitrile or 3-hydroxy-2-
naphthoic acid with benzene-1,2-diamine in PPA under microwave
irradiation; 2-(9-anthryl)-4,5-diphenylimidazole (11) and 2-(9-
anthryl)-phenanthroimidazole (9) were prepared according to
reference [28] by the condensation reaction of 9-anthraldehyde,
ammonium acetate and benzyl or phenanthrene-9,10-dione.
2.2.2.13. 2-(9-Anthryl)-1-n-pentyl-4,5-diphenylimidazole
(12b).
Compound 12b was obtained from 0.99 g (2.5 mmol) of 11 as
yellow solids in 48% yield. m.p. 175–176 ◦C. 1H NMR (CDCl3): 0.38
(t, J = 6.3 Hz, 3H, CH3), 0.56–0.65 (m, 4H, CH2), 0.98–1.08 (m, 2H,
CH2), 3.46 (t, J = 7.5 Hz, 2H, NCH2), 7.10–7.23 (m, 3H, ArH), 7.43–7.57
(m, 9H, ArH), 7.61–7.65 (m, 2H, ArH), 7.75–7.81 (m, 2H, ArH),
8.02–8.07 (m, 2H, ArH), 8.57 (s, 1H, ArH). 13C NMR (CDCl3): 13.4,
21.4, 28.2, 29.9, 44.7, 125.1, 125.3, 125.9, 126.1, 126.5, 126.7, 127.9,
128.4, 128.5, 128.8, 129.0, 129.1, 131.0, 131.2, 131.6, 131.9, 134.7,

Y.-N. Yan et al. / Spectrochimica Acta Part A 74 (2009) 233–242
237
Table 1
The ꢀamax, ε, ꢀem, Stokes shift, ˚F values, and the lifetime of fluorescence of some samples in ethyl acetate.
Sample
ꢀamax, nm
ε, 104 cm2 mol−1
ꢀem, nm
Stokes shift, nm−1
˚
F
T1/ns (Rel.%)
T2/ns (Rel.%)
2a
2b
2c
10a
10b
10c
12a
12b
12c
385
386
385
386
385
385
385
385
386
2.30
1.20
2.70
1.20
1.70
1.40
1.10
2.50
0.80
425
427
428
455
457
454
453
455
453
2445
2487
2610
3928
4093
3948
3899
3996
3831
0.53
0.51
0.48
0.51
0.44
0.40
0.28
0.26
0.25
1.40 (17.62)
1.52 (18.23)
1.76 (23.53)
2.24 (75.69)
2.36 (72.85)
2.31 (64.06)
2.08 (38.88)
2.11 (37.62)
1.90 (30.84)
5.02 (82.38)
5.22 (81.77)
5.40 (76.47)
5.25 (24.31)
6.34 (27.15)
6.18 (35.94)
5.87 (61.12)
5.82 (62.38)
5.74 (69.16)
The condensation reaction of 2-(phenoxymethyl)benzimidazole
with 9-anthraldehyde could be carried out easily by refluxing the
mixture of these two materials in acetic anhydride to form 2-(2-(9-
anthryl)-1-phenoxyvinyl)benzimidazole (7) in a yield of 40%. The
synthesis of 2-(2-(9-anthryl)vinyl)benzimidazole (3b) by the simi-
lar condensation of 2-methylbenzimidazole with 9-anthraldehyde
was also investigated under the same conditions, but no product
could be obtained. The reason could be that the activity of hydro-
gen atom on methyl of 2-methylbenzimidazole is lower than that of
hydrogen atom on methylene of 2-(phenoxymethyl)benzimidazole.
In order to get compound 3b, the below procedure was
attempted. 9-Anthraldehyde reacted with malonic acid in pyri-
dine firstly to offer 3-(9-anthryl)acrylic acid, then this acid reacted
with benzene-1,2-diamine to synthesize 3b as the similar reac-
tion to prepare 3a. However, 3b was still unable to be obtained,
although there are several reported methods about the con-
densation of arylacrylic acid with benzene-1,2-diamine in PPA
under microwave irradiation to generate the corresponding 2-
(2-(aryl)vinyl)benzimidazole compounds [37,42–45]. The reason
could be that these reported arylacrylic acids are stable under
the reaction conditions, but 3-(9-anthryl)acrylic acid could be so
unstable that it decomposed under this high-temperature and
strong-acidity condition before it formed benzimidazole com-
pound with benzene-1,2-diamine.
3.1.3. Bromination of
4,5-diphenyl-1-alkyl-2-(9-anthryl)imidazole
According to the reported method [45] in carbon disulfide, com-
pound 12a and 12c could be brominated smoothly on 10-position of
anthracene into 13a and 13b, which could offer an important pro-
cedure to prepare some OLED intermediate materials containing
imidazole or anthracene ring.
3.2. The solubility of the alkylated compounds
We found that all the 2-(9-phenanthrenyl)-, 2-(9-anthryl)-
and 2-(1-pyrenyl)- benzimidazole compounds or 4,5-diphenyl-
2-(9-anthryl)imidazole compounds possess a lower solubility in
ethyl acetate, chloroform, dichloromethane, ethanol, and ace-
tone, due to their large conjugated-structure. However, after these
compounds were alkylated by n-butylbromide, iso-butylbromide,
n-pentylbromide or n-dodecylbromide, respectively, to form
the corresponding 2-(9-phenanthrenyl)-, 2-(9-anthryl)- and 2-
(1-pyrenyl)-1-alkylbenzimidazole compounds or 4,5-diphenyl-1-
alkyl-2-(9-anthryl)imidazole, the solubility could be obviously
improved, so that they can be dissolved easily in ethyl acetate,
chloroform, dichloromethane, ethanol, and acetone. Therefore,
for 2-(9-phenanthrenyl)-, 2-(9-anthryl)-, 2-(1-pyrenyl)- benzim-
idazole, 2-(9-anthryl)phenanthroimidazole or 4,5-diphenyl-2-(9-
anthryl)imidazole compounds, the problem for their uses in many
fields due to the lower solubility could be solved by introducing a
suitable alkyl into 1-position.
3.1.2. Alkylation reaction of benzimidazole or imidazole
compounds
The imidazole compounds or benzimidazole compounds could
be alkylated as we ever reported [32–35], although heavy steric hin-
drance exists, especially in compound 11. Moreover, compounds 3a
could react with twice-fold amount of 1-bromobutane to form 4a.
The alkylation reaction of 1-nitrogen atom of benzimidazole and
oxygen atom of 2-naphthalenol occurred at the same time under
this condition. However, the reaction of 7 and 1-bromobutane
under the same condition was so complicated that the desired com-
pound, 2-(2-(9-anthryl)-1-phenoxyvinyl)-1-n-butylbenzimidazole
(8) could not be isolated.
The alkylation reactions of imidazole or benzimidazole com-
pounds above were carried out in butanone, the same reactions
were attempted in acetone in order to select a solvent which is
much easier to remove and much easier to obtain. The mixture of
2.5 mmol of imidazole, 3.5 mmol of alkyl bromide, 0.25 g of TBAB,
10 mL of 50% aqueous sodium hydroxide solution and 10 mL of
acetone was stirred at 40 ◦C for 36–48 h and the reacting mixture
was monitored by TLC. The same protocol was done as above. The
yields for 2a, 2b and 10a are 46%, 40% and 25%, respectively. The
yields were low, although the reaction times were prolonged. In
addition, this method for the alkylation reaction of 7 into 8 did
not work. To prepare compound 12, the solvent must be butanone
and the reaction temperature should be higher than 75 ◦C. There-
fore, butanone is better than acetone as solvent for the alkylation
reaction for these compounds, although acetone is cheaper than
butanone.
3.3. Spectral data
The concentrations of the samples for UV absorption and emis-
sion measurements were about 1 × 10−6 M in ethyl acetate. The data
for ꢀamax, ε, ꢀem values are presented in Tables 1 and 2 respectively.
The ˚F values were determined by the comparing method, using
coumarin 1 as a standard sample with ˚F = 0.99 in ethyl acetate
[46]. Fluorescence lifetime values (T) were determined in ethyl
acetate and in solid state respectively, both first-order-progression
diminishing lifetime (T1) values and second-order-progression
diminishing lifetime (T2) values were obtained, the related ratio
Table 2
The ꢀamax, ꢀem, Stokes shift, and the lifetime of fluorescence of some samples in solid
state.
Sample
ꢀamax, nm
ꢀem, nm
Stokes
T1/ns (Rel.%)
T2/ns (Rel.%)
shift, nm−1
2a
2b
2c
10a
10b
10c
12a
12b
12c
366
397
398
398
439
468
468
468
468
477
438
440
467
490
510
536
541
514
6813
2357
2398
3712
2371
1760
2711
2883
1912
3.34 (43.67)
1.89 (38.16)
1.94 (62.78)
1.82 (52.04)
11.41 (19.66)
6.81 (48.15)
8.37 (69.08)
9.81 (51.44)
6.96 (45.26)
16.38 (56.33)
8.61 (61.84)
5.89 (37.22)
7.73 (47.96)
23.20 (80.34)
19.19 (51.85)
24.02 (30.92)
25.21 (48.56)
24.46 (54.74)

238
Y.-N. Yan et al. / Spectrochimica Acta Part A 74 (2009) 233–242
Table 4
Selected bond lengths (Å) and angles (◦) for 12a.
Bond lengths
N(1)–C(30)
C(2)–C(4)
1.4650(18)
1.481(2)
C(1)–C(16)
C(3)–C(10)
1.4845(18)
1.4768(19)
Bond angles
N(1)–C(1)–C(16)
N(2)–C(3)–C(10)
C(1)–N(1)–C(30)
C(2)–N(1)–C(30)
123.87(12)
119.46(13)
126.20(12)
126.55(12)
N(1)–C(2)–C(4)
N(2)–C(1)–C(16)
C(2)–C(3)–C(10)
C(3)–C(2)–C(4)
119.66(12)
124.50(12)
130.54(13)
135.09(13)
Fig. 2. Structures of 1-alkyl-2-arylimidazole derivatives.
for both diminishing methods (T1, T2) are presented as percentage
in brackets in Tables 1 and 2.
3.4. The relationships between spectral behaviors and structures
3.4.1. The classes of the conjugated-system based on the scale or
size
Based on the scale or size of their conjugated-system, these
compounds reported here could be classified into three kinds,
2-(9-anthryl)-1-alkyl-benzimidazole 2a–2c (I), 2-(9-anthryl)-1-
alkyl-4,5-diphenylimidazole 12a–12c (II), and 2-(9-anthryl)-1-
alkylphenanthroimidazole 10a–10c (III) (Fig. 2).
The order of the scale or size of the conjugated-system of
compounds I–III with regard to their skeleton structure is as the
following: III > II > I.
Fig. 3. The single crystal structure of 12a.
3.4.2. The single crystal structure of 12a
Single crystals of 12a suitable for X-ray structural analysis
were obtained by evaporation of ethanol solution. The diffrac-
tion data for both structures were collected with an Bruker Smart
1000 CCD X-ray single crystal diffractometer using a graphite
monochromated Mo K␣ radiation (ꢀ = 0.71073 Å) at 173(2) K. The
structures were solved by direct methods with SHELXS-97 pro-
gram and refinements on F2 were performed with SHELXL-97
program by full-matrix least-squares techniques with anisotropic
thermal parameters for the nonhydrogen atoms. All H atoms were
initially located in a difference Fourier map. A summary of the
crystallographic data and structure refinement details is given in
Tables 3 and 4.
The crystal structure and cell structure of 12a are shown in
Figs. 3 and 4, respectively. The dihedral angle between the ring A
and ring B is 4.1◦, 100.7◦ for ring C, and 78.4◦ for ring D (Fig. 5).
So, plane A and plane B are nearly coplanar, plane A and plane C or
plane A and plane D are basically vertical each other.
Because planes B, C and D are attached on plane A with single
bond, these three planes could turn around plane A. It could be
found from the molecular structures in Fig. 2 that there is a steric
hindrance between hydrogen atom on 9-position of anthracene
and alkyl group on 1-positoin of imidazole in the molecular struc-
tures of 2a–2c(I), 12a–12c(II) and 10a–10c(III). Besides this steric
hindrance, there is another steric hindrance between a hydrogen
atom on 1-position of phenanthrene and alkyl group on 1-positoin
of imidazole in the molecular structures of compound III. In the
molecular structures of compound II, there are two other steric hin-
drances respectively between two hydrogen atoms on 2-position of
two benzene rings on 4- and 5-position of imidazole and between
hydrogen atom on 6-position of benzene ring on 4-position of imi-
dazole and alkyl group on 1-positoin of imidazole. Therefore, the
Table 3
Crystal data and structure refinement for 12a.
Empirical formula
Formula weight
C33H28N2
452.57
Temperature (K)
173(2)
Crystal system, space group
Triclinic, P-1
Unit cell dimensions
a (Å)
8.0636(11)
b (Å)
9.2636(13)
c (Å)
16.702(2)
86.465(2)
84.996(2)
80.368(2)
1223.9(3)
1.228
0.071
480
˛ (◦)
ˇ (◦)
ꢁ (◦)
Volume (Å3), Z
DCalc (Mg/m3)
Absorption coefficient (mm−1
F (0 0 0)
)
Crystal size (mm)
 range for data collection (◦)
Limiting indices
Reflections collected/unique
Completeness to theta = 27.11
Refinement method
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I>2sigma(I)]
R indices (all data)
0.48 × 0.40 × 0.37
1.23–27.11
−10 ≤h ≤10, −11 ≤k ≤11, −21 ≤l ≤21
10330/5263 [R(int) = 0.0214]
97.6%
Full-matrix least-squares on F2
5263/0/316
1.068
R1 = 0.0465, wR2 = 0.1322
R1 = 0.0662, wR2 = 0.1529
0.242 and −0.273
733834
Largest diff. peak and hole (eÅ−3
CCDC
)
Fig. 4. The cell structure of 12a.

Y.-N. Yan et al. / Spectrochimica Acta Part A 74 (2009) 233–242
239
conjugated-system size. Therefore, the order for the ꢀamax, ꢀem and
values of these four kinds of compounds should be the same
˚
F
as the order of their conjugated-system size: III > II > I. However,
we found that the ꢀamax, ꢀem and ˚F values for these compounds
did not keep this order by comparing their spectral data in Table 1.
This is because that the molecules of these compounds investigated
here could not be in one plane, the conjugate-system was broken
between imidazole and aromatic group attached on the 2-position
of imidazole, so that the scale or size of the conjugated-system
could not effectively increase with the increase of the number of
aromatic ring.
Here, the ꢀamax values of these nine compounds are almost the
same, which coincides with the research [47,48] on anthracene-
containing supramolecular complexes reported by W.Y. Wong.
On the other hand, the ˚F values of organic compounds are
not only related to the size of their conjugated-system, but also
related to the rigidity (or the coplanarity) of their molecular struc-
ture. Comparing the structure I with III in Fig. 2, we could find that
there is a same steric hindrance between the hydrogen atom on
9-position of anthracene and the alkyl group on 1-position of imid-
zole in both structures I and III, moreover, there is another steric
hindrance between the hydrogen atom on 1-position of phenan-
threne and the alkyl group on 1-position of imidzole in structure
III. Therefore, the tension from intramolecular steric hindrance is
larger in structure III than that in I, and the tension would make the
molecule twist out of a plane in structure III more than in structure
I, the ˚F values of compounds in structure III are lower than that
of compounds in structure I.
From Fig. 2, we could find that the ˚F values of III should be
higher than that of II, because the molecular structures of III possess
a larger rigid conjugated-system than that of II, due to the more
heavy steric hindrance between the two benzene rings on 4- and 5-
position of the imidazole ring in molecular structures of II and also
the free rotation of these two benzene rings around the imidazole
ring.
Fig. 5. Dihedral angle values of 12a.
coplanarity of the molecular structures of compounds II and III
would be destroyed much more than that of the molecular structure
of I.
We have previously reported a crystal structure of 2-(4-
carboxyphenyl)-1-n-butyl 4,5-diphenylimidazole (CPBDPI) and
related dihedral angles (Fig. 6) [36]. Comparing the corresponding
dihedral angles of CPBDPI with the angles of 2-(9-anthryl)-1-
n-butyl-4,5-diphenylimidazole (12a, Fig. 4), it is found that the
dihedral angle (78.4◦) of imidazole (A) to 2-(9-anthryl) (D) in 12a is
bigger than that (55.545◦) of imidazole (A) to 2-(4-carboxyphenyl)
(D) in CPBDPI. This is because that hydrogen atom on 9-position of
anthracene is much closer to alkyl group on 1-positoin of imida-
zole in 12a (Fig. 4) than hydrogen atom on 2-position of phenyl to
alkyl group on 1-positoin of imidazole in CPBDPI (Fig. 6), the steric
hindrance between hydrogen atom on 9-position of anthracene and
alkylgroupon1-positoinofimidazoleismuchmoreheavythanthat
between hydrogen atom on 2-position of phenyl and alkyl group
on 1-positoin of imidazole in CPBDPI. Therefore, the two planes of
anthracene (D) and imidazole (A) in 12a would be twisted much
more than the two planes of benzene (D) and imidazole (A) in
CPBDPI from one plane.
3.4.4. The effect of alkyl on spectral behaviors
We could find from Table 1 that the ꢀamax and ꢀem values for 2a,
2b and 2c, containing the same skeleton structure, are very close
to each other, although they possess different alkyl group (2a n-
butyl, 2b iso-butyl and 2c n-dodecyl). The same situation could be
found in 10a, 10b and 10c or in 12a, 12b and 12c. Therefore, it could
be deduced that the alkyl group did not play an important role on
ꢀamax and ꢀem values although the bulk of these alkyl groups are
different.
3.4.3. The effect of main skeleton of conjugated-system on
spectral behaviors
According to the theory of the relationship between the struc-
tures of the conjugated-system and spectral properties, the ꢀamax
,
ꢀem and ˚F values should all increase with the increase of the
As to the ˚F values, it could be found from Table 1 that the
˚F values decreased with the increasing volume of the alkyl group
attached on 1-position of imidazole. The ˚F values for 2a, 2b and
2c are 53%, 51% and 48%, respectively; for 10a, 10b and 10c, 51%,
44% and 40%, respectively; for 12a, 12b and 12c, 28%, 26% and 25%,
respectively. This is because the large volume of the alkyl group
would make the molecule twist much more violently out of a plane,
which would obviously reduce the ˚F values of organic material.
Therefore, for 2a–2c, 10a–10c and 12a–12c, the ˚F values would
decrease with the increasing volume of the alkyl group attached on
the 1-position of imidazole.
3.5. Comparisons of the ꢀamax and ꢀem values in solution with
these values in solid state
It could be found from Tables 1 and 2 that the ꢀamax and ꢀem
values of compounds 2a–2c, 10a–10c and 12a–12c in ethyl acetate
are smaller than that in solid state, expect for the ꢀamax value of 2a.
Comparing the Stokes shift values of these compounds in ethyl
acetate and in solid state, no regularity could be found.
Fig. 6. Dihedral angles of CPBDPI [36].

240
Y.-N. Yan et al. / Spectrochimica Acta Part A 74 (2009) 233–242
3.6. The fluorescence lifetime values
second-order progression), are measured. In this work, T1 and
T2 values were determined in ethyl acetate and in solid state
respectively, the ratio for two diminishing patterns (first-order-
progression and second-order-progression) were determined at the
same time and the values were given as related percentage in brack-
ets.
In general, for organic materials, two diminishing patterns
(first-order-progression and second-order-progression) of fluores-
cence intensity are considered and two kinds of fluorescence
lifetime values, T1 (fluorescence lifetime diminished in first-
order progression,) and T2 (fluorescence lifetime diminished in
We could find the following results from Tables 1 and 2:
Fig. 7. TGA and DTG curves of samples 2a, 10a, 10b, 12a, and 12b.

Y.-N. Yan et al. / Spectrochimica Acta Part A 74 (2009) 233–242
241
Table 5
For 2-(9-phenanthrenyl)-, 2-(9-anthryl)- and 2-(1-pyrenyl)-
benzimidazole compounds, 2-(9-anthryl)phenanthroimidazole
compounds and 4,5-diphenyl-2-(9-anthryl)imidazole compounds,
they could not be used in many fields due to their low solubility.
This problem could be solved effectively by introducing some
suitable alkyl groups.
The decomposition temperature and thermal weightlessness percentage for 2a, 10a,
10b, 12a, and 12b.
Sample
2a
10a
10b
12a
12b
Decomposition temperature (◦C)
Weightlessness (%)
360.2
423.8
1.46
277.0
418.3
2.83
294.0
392.5
0.94
220.1
386.5
1.01
283.0
0.94
Weightlessness temperature (◦C) 220.9
2-(10-Bromo-9-anthracenyl)-1-alkylbenzimidazole
pounds could be prepared easily by ordinary bromination
reaction of 2-(9-anthracenyl)-1-alkyl-benzimidazole com-
com-
(1) In ethyl acetate, for every compound, the T1 values are all
smaller than the corresponding T2 values; in general, the T1
values of 10a–10c are larger than those of 12a–12c and the T1
values of 12a–12c are larger than those of 2a–2c; for the T2
values, the same sequence could be found as for the T1 values.
We found from Table 1 that second-order-progression dimin-
ishing is the main pattern for 2a–2c and 12a–12c in ethyl
acetate, while first-order-progression diminishing is the main
pattern for 10a–10c. Comparing the main molecule-skeleton
structures of 2a–2c and 12a–12c with those of 10a–10c (Fig. 5),
we could find that, besides a anthracene unit on 2-positon
of imidazole, there is a benzoimidazole unit in 2a–2c, a 4,5-
diphenylimidazole unit in 12a–12c and a phenanthroimidazole
unit in 10a–10c. The phenanthroimidazole unit possesses a
larger and rigider conjugated-system than benzoimidazole unit
or 4,5-diphenylimidazole unit.
pounds and bromine in carbon disulfide, which could offer
an efficient method to prepare some organic intermediate
2-(10-bromo-9-anthracenyl)-1-alkylbenzimidazole compounds.
For 4,5-diphenyl-1-n-butyl-2-arylimidazole compounds, the
dihedral angle of imidazole and 2-aryl would increase with the
increase of steric hindrance between the alkyl on 1-position and the
aryl on 2-position, and the aromatic unit introduced on 2-position
could not conjugate effectively with benzimidazole or imidazole.
Therefore, it is not a good method to change their ꢀa, ꢀe and ˚F val-
ues by introducing some larger conjugated-system aromatic unit to
the 2-position of benzimidazole or imidazole.
5. Supplementary material
The crystallographic data (excluding structure factors) of 12a
have been deposited with the Cambridge Crystallographic Cen-
ter as supplementary publication no. CCDC 733834. Copy of
this information may be obtained free of charge via www:
http://www.ccdc.cam.ac.uk or from The Director, CCDC, 12 Union
Road, Cambridge CB221EZ, UK (fax: +44 1223 336033; email:
deposit@ccdc.cam.ac.uk). Structural factors are available on request
from the authors.
The alkyl groups did not obviously affect the T1 or T2 values
of these compounds in ethyl acetate.
(2) In solid state, for the effects of main skeleton and alkyl group of
these compounds on the T1 or T2 values, there are not regular
patterns. Regard to the diminishing patterns of first-order-
progression and second-order-progression there is still not any
regular sequence.
(3) Comparing the T1 or T2 values of these compounds in ethyl
acetate with those values in solid state, we could find that the
T1 or T2 values in solid state are generally larger than those in
ethyl acetate.
Acknowledgment
This project is supported by Scientific and Technical
Project Foundation of Guangdong Province (2003C103006 and
2007B060401068).
3.7. Thermal stability
An organic phosphor applied in the fabricated LEDs and OLEDs
is required to possess a high thermal stability. In order to inves-
tigate the thermal stability of the synthesized compounds, the
thermogravimetric analysis (TGA) and differential thermogravi-
metric (DTG) techniques were employed and five samples, 2a, 10a,
10b, 12a, and 12b, were measured, their TGA and DTG curves are
shown in Fig. 7.
The decomposition temperature and thermal weightlessness
percentage for these five samples could be found from the corre-
sponding curve, respectively, and they are listed in Table 5.
It could be found from Table 5 that the decomposition temper-
ature for five samples are all more than 350 ◦C, and from Fig. 7 that
the starting temperature for thermal weightlessness for five sam-
ples is more than 165 ◦C, which demonstrate that these samples are
thermally stable to be used in LEDs and OLEDs.
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