Photophysical processes of a fluorene derivative containing carbazole unit

Article abstract of DOI:10.1016/j.saa.2004.06.037

The photoluminescence properties of 9,9-bis[4′-(9″-carbazovinylene)phenyl]fluorene (F-CZV) formed by Heck reaction of 9,9-bis(4′-iodophenyl)fluorene (F-IP) and N-vinylcarbazole have been carefully studied. The results show that the compound emits blue light and the dimolecular excimer is formed with gradual increase in concentration of F-CZV. The results also indicate the interaction between F-CZV and electron donors (N,N-dimethylaniline) or electron acceptors (dimethylterephthalate, fullerene carbon nanotubes) can be efficiently generated where the processes follow the Stern-Volmer equation. Moreover, when dimethylterephthalate (DMTP) or carbon nanotubes (CNTs) is gradually added into the solution of F-CZV, the emission intensities of fluorescence are unusually increased. But when concentration of dimethylterephthalate or carbon nanotubes beyond a certain scope, the emission intensities of fluorescence are gradually decreased.

Full text of DOI:10.1016/j.saa.2004.06.037

Spectrochimica Acta Part A 61 (2005) 1171–1174
Photophysical processes of a fluorene derivative containing carbazole unit
Liheng Feng, Caihong Zhang, Hongyan Bie, Zhaobin Chen∗
aSchool of Chemistry and Chemical Engineering, University of Shanxi, Taiyuan 030006, PR China
Received 5 April 2004; accepted 10 June 2004
Abstract
The photoluminescence properties of 9,9-bis[4ꢀ-(9ꢀꢀ-carbazovinylene)phenyl]fluorene (F-CZV) formed by Heck reaction of 9,9-bis(4ꢀ-
iodophenyl)fluorene (F-IP) and N-vinylcarbazole have been carefully studied. The results show that the compound emits blue light and the
dimolecular excimer is formed with gradual increase in concentration of F-CZV. The results also indicate the interaction between F-CZV and
electron donors (N,N-dimethylaniline) or electron acceptors (dimethylterephthalate, fullerene carbon nanotubes) can be efficiently generated
where the processes follow the Stern–Volmer equation. Moreover, when dimethylterephthalate (DMTP) or carbon nanotubes (CNTs) is
gradually added into the solution of F-CZV, the emission intensities of fluorescence are unusually increased. But when concentration of
dimethylterephthalate or carbon nanotubes beyond a certain scope, the emission intensities of fluorescence are gradually decreased.
© 2004 Elsevier B.V. All rights reserved.
Keywords: 9,9-bis(4ꢀ-Aminophenyl)fluorene; Vinylcarbazole; Fullerene; Carbon nanotubes; Excimer; Interaction
1. Introduction
late (DMTP), fullerene (C60), carbon nanotubes (CNTs) are
studied.
It is well known that a good photoluminescence mate-
rial should possess high photoluminescence efficiency, excel-
lent charge transport ability and film-forming property [1,2].
Carbazole and its derivatives are good hole-transport mate-
rials and have been used in construction of light-emitting
device (LEDs) [3,4]. Although a great number of organic
compounds containing carbazole unit have been synthesized
and the photoluminescence properties have also been investi-
gated, the studies on synthesis and photoluminescence prop-
erties of new carbazole-containing compound are yet a sig-
nificant subject [5,6].
In the paper, a novel compound, F-CZV, consisting of
vinylcarbazole moiety that can form high quality thin films
with excellent hole-transporting function and fluorene moiety
that emits blue fluorescence with high quantum yield is syn-
thesized. The photoluminescence properties of F-CZV are in-
vestigated. The concentration-dependent photoluminescence
of F-CZV is also examined. Furthermore, the interactions of
F-CZV and N,N-dimethylaniline (DMA), dimethylterephtha-
2. Experimental
2.1. Materials and measurements
Dichloromethane, ethyl acetate, acetonitrile and DMA are
analytical grade reagents and treated according to standard
method used before, fullerene (C60) and carbon nanotubes
(CNTs) are obtained from Term Co. in a purify of 99% and
90%, respectively, which are all applied to measurement of
the light-emitting properties.
The measurements of fluorescence are performed on a
Perkin-Elmer LS-50B fluorometer. Both excitation and emis-
sion bands are set at 5 nm on these experimental conditions.
All the experiments are carried out at 20 1 ◦C.
2.2. Synthesis
9,9-bis(4ꢀ-Iodophenyl)fluorene (F-IP) and 9,9-bis[4ꢀ-(9ꢀꢀ-
carbazovinylene)phenyl]fluorene (F-CZV) are prepared by
our research group according to the route shown in Scheme 1
∗
Corresponding author. Tel.: +86 351 7011492; fax: +86 351 7011688.
E-mail address: zchen@sxu.edu.cn (Z. Chen).
1386-1425/$ – see front matter © 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2004.06.037

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L. Feng et al. / Spectrochimica Acta Part A 61 (2005) 1171–1174
Fig. 2. Absorption and emission spectra of F-CZV in ethyl acetate. Concen-
tration of F-CZV, 1.50 × 10−7 M.
F-CZVshownarered-shiftedandtheabsorptionspectrablue-
shifted. These phenomena can be attributed to their different
configuration, greater ␲-system conjugation length in F-CZV
than that in F-IP.
3.2. Concentration effects on photoluminescence and
formation of excimer
For understanding deeply the photoluminescence prop-
erties of F-CZV the concentration effects on photolumines-
cence of F-CZV are investigated. Fig. 3 shows the emission
spectra of F-CZV in dichloromethane with different concen-
trations. It can be seen when concentration of F-CZV is in
low concentration 1.28 × 10−7 M, the maximal fluorescence
emission is at 356 nm (length wave peak), and the emission
intensities of F-CZV are increasing with the increase in con-
centration of F-CZV, as shown in 1–3 lines. On progressive
increase in concentration of F-CZV, the shorter wave peaks
(340 nm) of fluorescence are vanished and the length wave
peaks (356 nm) are red-shifted to 370 nm. Moreover, with
continuously progressive increase in concentration of F-CZV
the fluorescence peaks at 370 nm of F-CZV are quenched ef-
ficiency and a new emission band appears at the relatively
longer wavelength 440 nm and all pass an isostilbic point
401 nm. Evidently, the new emission band can contribute to
the excimer formed between two F-CZV molecules.
Scheme 1. The synthetic route of F-CZV in the study.
[7]. The yield of F-IP is 81.5%, mp 183–184; the yield of
F-CZV is 16.4%, mp 194–195 ◦C.
3. Results and discussion
3.1. Absorption and fluorescence emission spectrum
The UV–Vis absorption and fluorescence emission spectra
of F-IP and F-CZV in ethyl acetate are shown in Figs. 1 and 2,
respectively. It can be seen from Fig. 1 that the maximum
absorption and emission peaks of F-IP are at 310 and 330 nm,
respectively. As shown in Fig. 2 the maximum absorption and
emission peaks of F-CZV are at 290 and 356 nm, respectively.
By comparison with compound F-IP, the emission spectra of
Fig. 3. Emission spectra of F-CZV solution in dichloromethane with differ-
ent concentration (M) and its excimer: (1) 4.28 × 10−8; (2) 8.56 × 10−8
;
(3) 1.28 × 10−7; (4) 6.84 × 10−5; (5) 7.32 × 10−4; (6) 2.22 × 10−4; (7)
Fig. 1. Absorption and emission spectra of F-IP in ethyl acetate. Concentra-
tion of F-IP, 6.23 × 10−5 M.
8.46 × 10−3
.

L. Feng et al. / Spectrochimica Acta Part A 61 (2005) 1171–1174
1173
Fig. 6. Fluorescence spectra of F-CZV at different concentration of C60
.
Fig. 4. Fluorescence spectra of F-CZV at different concentration of DMA.
Concentration of F-CZV, 2.57 × 10−7 M. Concentration of DMA (mol/L,
M): (0) 0.00; (1) 6.72 × 10−5; (2) 1.34 × 10−4; (3) 2.02 × 10−4; (4) 2.69
Concentration of F-CZV, 1.71 × 10−7 M. Concentration of C60 (mol/L, M):
(0) 0.00; (1) 3.71 × 10−7; (2) 8.34 × 10−7; (3) 1.30 × 10−6; (4) 2.22 ×
10−6; (5) 3.15 × 10−6; (6) 5.47 × 10−6; (7) 7.32 × 10−6
.
× 10−4; (5) 3.36 × 10−4
.
ergy of F-CZV that results from the action between F-CZV
and solvent is deliveried, which would lead to increasing of
fluorescence intensity of carbazole units. When the concen-
tration of DMTP goes beyond a certain scope, the excess
DMTP units would act as quencher to quench gradually the
fluorescence of F-CZV.
3.3. The quenching process of fluorescence of F-CZV
with DMA and DMTP
N,N-Dimethylaniline (DMA) is a typical electron donor
and dimethylterephalate (DMTP) is a typical electron ac-
ceptor. When DMA is added to a solution of F-CZV
in dichloromethane, the fluorescence of F-CZV is effi-
ciently quenched and the quenching process follows the
Stern–Volmer equation. The apparent quenching coefficient,
Ksv, is 7.24 × 103 M−1 and no exciplex emission spectra are
observed (as shown in Fig. 4). In order to go further into the
fluorescence quenching of F-CZV, the quenching process of
F-CZV with DMTP is also examined and shown in Fig. 5.
It can be seen that the emission intensity of fluorescence are
initially increased and then decreased with gradual increas-
ing in concentration of DMTP in dichloromethane. Mean-
while, the emission peaks at 356 nm shown are red-shifted to
about 30 nm, while short wave peaks (340 nm) are vanished.
From the experimental facts and references an explanation
is proposed: carbazole unit is an electron donor group and a
typical hole transporting molecule while dimethylterephalate
(DMTP) is a good electron acceptor, so the strong interac-
tion between carbazole and DMTP happens when DMTP is
gradually added into the solution of F-CZV, the potential en-
3.4. Interaction between F-CZV and fullerene (C60)
C60 bears many unusual electrochemical and electronic
properties. One of the most remarkable properties of C60 re-
lated to electron transfer phenomena is that it can efficiently
induce a rapid charge separation and a further slow charge
recombination [8]. In the experiment, the interactions of F-
CZV with C60 are examined. The results are shown in Fig. 6.
As we have seen in Fig. 6, ‘0’ is F-CZV in concentration
1.71 × 10−7 mol/L (M) without C60, ‘1–7’ are F-CZV in
the present in different concentration of C60. With the grad-
ual increasing of concentration of C60, the fluorescence of
F-CZV is quenched efficiently and the process follows the
Stern–Volmer equation F0 /FM = 1 + K[Q] (Fig. 8). The ap-
M
SV
parent quenching constant is 4.06 × 105 M−1, which suggests
that the strong interactions between excited F-CZV and C60
happen. It is well known that both F-CZV and C60 have a
large ␲-conjugated system in which the ␲–␲ interaction may
Fig. 5. Fluorescence spectra of F-CZV at different concentration of DMTP.
Concentration of F-CZV, 1.07 × 10−7 M. Concentration of DMTP (mol/L,
M), (0) 0.00; (1) 3.77 × 10−7; (2) 5.66 × 10−7; (3) 2.56 × 10−4; (4) 3.49
Fig. 7. Fluorescence spectra of F-CZV at different concentration of CNTs.
Concentration of F-CZV 1.71 × 10−7 M.
× 10−4; (5) 6.71 × 10−4; (6) 1.05 × 10−3; (7) 1.61 × 10−3
.

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L. Feng et al. / Spectrochimica Acta Part A 61 (2005) 1171–1174
in dichloromethane. Meanwhile, the emission peaks shown
are red-shifted. The phenomenon may have resulted from car-
bon nanotubes unique structures and cavity dimension scale
[10,11]. Further research toward a better understanding of
this action is currently in progress.
Acknowledgements
The present work was supported by the Natural Science
Foundation of China (30000112); Laboratory of Organic
Solid, Chinese Academy of Sciences and The Returned Stu-
dent Science Foundation of Shanxi Province of China.
Fig. 8. Dependence of FM0 /FM concentration of C60. Concentration of F-
CZV, 1.71 × 10−7 M.
change the configuration of F-CZV. On the other hand, the
photoinduced charge transfer from excited F-CZV to C60 is
rapid. Upon this charge transfer the conjugated system may
be dramatically modified [9]. The processes will compete
with the radiative emission of F-CZV. So, the fluorescence is
quenched by adding C60.
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