Synthesis, characterization and photophysical processes of fluorene derivative containing naphthalene nucleus

Article abstract of DOI:10.1016/j.saa.2004.08.025

A novel luminescent compound, 9,9-bis[4′-(β-naphthyl-methacrylate)phenyl]fluorene (F-NMAP) is synthesized by Heck reaction of β-naphthyl methacrylic ester (NMAE) and 9,9-bis(4′-iodophenyl)-fluorene (BIPF). The structure is characterized by MS, ¹H NMR, IR, and UV-vis spectroscopy. The photophysical processes of F-NMAP have been carefully investigated by UV-vis absorption and fluorescence spectra. The results show that the compound emits blue and blue-violet light. The luminescence quantum yield is 0.652 in ethanol and the emission spectra exhibit obvious solvent effect. With the increase in polarity of solvents, the fluorescence spectra change obviously and appear blue shift at room temperature. The light emitting can be quenched by both electron donor, N,N-dimethylaniline (DMA), and electron acceptor, dimethylterephthalate (DMTP). On adding gradually, DMA or DMTP into the solution of F-NMAP, the emission intensities of fluorescence are unusually increased. But when the concentration of DMA or DMTP goes beyond a certain scope, the emission intensities of fluorescence are gradually decreased. Simultaneously, the maximum emission peaks of F-NMAP-added DMA are blue-shifted and the maximum emission peaks of F-NMAP-added DMTP are red-shifted, respectively. Moreover, interactions between F-NMAP and fullerene (C₆₀), or carbon nanotubes (CNTs) are also studied by fluorescent quenching where the processes follow the Stern-Volmer equation.

Full text of DOI:10.1016/j.saa.2004.08.025

Spectrochimica Acta Part A 61 (2005) 2505–2509
Synthesis, characterization and photophysical processes of fluorene
derivative containing naphthalene nucleus
Liheng Feng, Zhaobin Chen∗
School of Chemistry and Chemical Engineering, Shanxi University, Taiyuan 030006, PR China
Received 20 July 2004; accepted 31 August 2004
Abstract
A novel luminescent compound, 9,9-bis[4ꢀ-(␤-naphthyl-methacrylate)phenyl]fluorene (F-NMAP) is synthesized by Heck reaction of ␤-
naphthyl methacrylic ester (NMAE) and 9,9-bis(4ꢀ-iodophenyl)-fluorene (BIPF). The structure is characterized by MS, H NMR, IR, and
1
UV–vis spectroscopy. The photophysical processes of F-NMAP have been carefully investigated by UV–vis absorption and fluorescence
spectra. The results show that the compound emits blue and blue-violet light. The luminescence quantum yield is 0.652 in ethanol and the
emission spectra exhibit obvious solvent effect. With the increase in polarity of solvents, the fluorescence spectra change obviously and
appear blue shift at room temperature. The light emitting can be quenched by both electron donor, N,N-dimethylaniline (DMA), and electron
acceptor, dimethylterephthalate (DMTP). On adding gradually, DMA or DMTP into the solution of F-NMAP, the emission intensities of
fluorescence are unusually increased. But when the concentration of DMA or DMTP goes beyond a certain scope, the emission intensities
of fluorescence are gradually decreased. Simultaneously, the maximum emission peaks of F-NMAP-added DMA are blue-shifted and the
maximum emission peaks of F-NMAP-added DMTP are red-shifted, respectively. Moreover, interactions between F-NMAP and fullerene
(C60), or carbon nanotubes (CNTs) are also studied by fluorescent quenching where the processes follow the Stern–Volmer equation.
© 2004 Elsevier B.V. All rights reserved.
Keywords: ␤-Naphthol; Methacrylic ester; Fullerene (C60); Interaction; 9,9-Bis(4ꢀ-iodophenyl)fluorene; Carbon nanotubes (CNTs)
1. Introduction
of fluorene can improve the solubility and processibility of
luminescent material without significant increase in steric
interactions in the luminescent material backbone [7]. As a
result, luminescent materials of fluorene have emerged as the
most attractive blue-emitting materials due to their high ef-
ficiency and good thermal stability. In addition, naphthalene
and its derivatives are not only useful organic dyes, but also
charge-transfer materials in electrophotography and electro-
luminescence [8–10].
In this paper, we report the synthesis and charac-
terization of a novel compound, 9,9-bis[4ꢀ-(␤-naphthy-
lmethacrylate)phenyl]fluorene (F-NMAP) consisting of
9,9-diphenylfluorene (DPF) moieties, which have high lu-
minescent efficiency and good thermal stability and ␤-
naphthyl methacrylic ester (NMAE) moieties, which is an
important high luminescent efficient blue light material.
The photophysical properties are investigated carefully. The
photoluminescence (PL) of F-NMAP are examined in dif-
ferent solvents. The quenching processes of F-NMAP with
Recently, the field of research into photoluminescent (PL)
and electroluminescent (EL) materials is growing rapidly due
to the versatility and potential applications of these com-
pounds [1–3]. A great number of luminescent compounds
have been synthesized and investigated; however, the search
fornewcompoundsthatpossessthecombineddesirableprop-
erties, such as high brightness and luminescent efficiency, and
good film-forming properties remains a big challenge in this
area [4–6]. Therefore, to meet the requirements of lumines-
cent materials, combination of two functional groups may be
a useful approach.
Fluorene derivatives show unique chemical and physi-
cal properties because they contain a rigid planar biphenyl
unit, and the facile substitution at the remote C9 position
∗
Corresponding author. Tel.: +86 351 7011 492; fax: +86 351 7011 688.
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.2004.08.025

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L. Feng, Z. Chen / Spectrochimica Acta Part A 61 (2005) 2505–2509
electron donor N,N-dimethylaniline (DMA), and electron ac-
ceptor dimethylterephthalate (DMTP) are studied. Moreover,
the molecular interactions of F-NMAP with fullerene (C60)
and carbon nanotubes (CNTs) are also investigated.
on a Shimadzu UV-265 spectrophotometer and Perkin-Elmer
LS-50B spectrophotometer, respectively. Both excitation and
emissionbandsaresetat5 nm. Alltheexperimentsarecarried
out at 20 1 ◦C.
2.2. Synthesis
2. Experimental
2.2.1. β-Naphthyl methacrylic ester (NMAE) [11]
DMAE are synthesized by amidation reaction between
␤-naphthol and methacryloylchloride in the presence of tri-
ethylamine in 85.3% yield.
2.1. Materials and measurements
The reagents and chemicals for preparation of monomer
and polymer are used as received, unless noted otherwise.
Methanol, ethanol, acetonitrile, ethyl acetate, THF, ether, cy-
clohexane are purchased from Beijing Chemical Plant and
treated according to standard methods used before, which are
all applied to measurement of the light-emitting properties.
The synthetic routes used are shown in Scheme 1.
Melting points are determined on a Sanyo Gallenkamp
MPD350 melting point apparatus and uncorrected. The IR
spectra are determined on a PE-1700 IR spectrophotometer
2.2.2. 9,9-Bis(4ꢀ-iodophenyl)fluorene (BIPF) [12]
BIPF could be obtained via the diazotization reac-
tion by employing the 9,9-bis(4ꢀ-aminophenyl)fluorene and
NaNO3/H2SO4/KI in 81.5% yield.
2.2.3. 9,9-Bis[4ꢀ-(β-naphthylmethacrylate)phenyl]-
fluorene (F-NMAP) [13]
A mixture of anhydrous palladium acetate (0.0112 g,
9,9-bis(4ꢀ-iodophenyl)fluorene
(1.45 g,
1
0.05 mmol),
by dispersing samples in KBr disks. H NMR spectra are
2.5 mmol), sodium acetate (0.4 g, 5 mmol) and ␤-naphthyl
methacrylic ester (4.00 g, 5.0 mmol) are dissolved in 300 mL
anhydrous DMF and stirred at 140 ◦C under a nitrogen
measured on a Bruker ARX300 spectrometer with DMSO
as solvent. Mass spectrum dates are obtained on a JEOL
GC–MS D300. UV–vis and fluorescence spectra are obtained
Scheme 1. The synthesis of NMAE, BIPF, F-NMAP.

L. Feng, Z. Chen / Spectrochimica Acta Part A 61 (2005) 2505–2509
2507
NMAP is slightly blue-shifted with the increase in the solvent
polarity. This can be explained as following: the molecular
structure of F-NMAP has heteroatomic carbonyl units, which
makes the (n–␲*) excited state plays a more important role
in the F-NMAP than the (␲–␲*) state. In addition, it is well
known that the solvolytic actions between unshared electron-
pairs and polar solvent have obviously happened, which will
reduce the energy of the n orbital. Thus, more energy will be
needed for this transition of electron from the n orbital to the
*
␲ orbital in a solvent with large polarity, as compared with
the transition in a solvent with small polarity, which means
*
that the energy gap between n and ␲ orbital increase with
the increasing of solvent polarity. Therefore, the emission
spectra of F-NMAP are slightly blue-shifted [14].
Fig. 1. Absorption and emission spectra of F-NMAP in ethanol. Concentra-
tion of F-NMAP, 4.27 × 10−7 mol/L (M).
atmosphere for 48 h. After addition of water to the reaction
mixture, the precipitate is collected by filtration. The
brown solid is dissolved in ethanol and poured into 300 mL
distilled water. The solid product is isolated by filtration and
purified by column chromatography on silica gel with ethyl
acetate:petroleum ether (1:9) as the eluant to give slightly
purple-yellow crystals in 27.6% yield; m.p.: 182–183 ◦C.
MS (EI, m/z): 709 (M-2CH3), 443 (M-2CH3-2C10H7);
1H NMR (DMSO, ppm) δ: 7.09–7.86 (32H, aromatic and
3.3. Quantum yield of photoluminescence
The fluorescence quantum yield is measured by relative
method using the quinine sulfate as the standard (0.546 in
0.5 mol/L H2SO4) [15]. The quantum yield is calculated from
the following equation:
ꢀ
Fr As ns
ꢁ2
Fs Ar nr
Φs = Φr
olefin), 2.17 (6H, 2CH3); IR (KBr, cm−1): 3208 (
1623 (C O), 1598, 1515, 1462, 1434 ( ), 1390 (CH3).
),
In the above expression, Φs is the fluorescent quantum
yield, F the integration of the emission intensities, n the index
of refraction of the solution, and A the absorbance of the
solution at the exciting wavelength. The subscripts r and s
denote the reference and unknown samples, respectively. The
values of quantum yield of F-NMAP in different solvents are
listed in Table 1.
3. Results and discussion
3.1. Absorption and fluorescence emission spectra
The UV–vis absorption and fluorescence emission spectra
of F-NMAP in ethanol are shown in Fig. 1. It can be seen
from Fig. 1 that the maximum absorption and emission peaks
are at 230 and 363 nm, respectively. This shows that the F-
NMAP emits blue and blue-violet light and is a desirable
blue-emitting photoluminescence material.
3.4. Interaction of F-NMAP with N,N-dimethylaniline
(DMA) and dimethylterephthalate (DMTP)
N,N-Dimethylaniline (DMA) is a typical electron donor
and dimethylterephalate (DMTP) is a typical electron accep-
tor. The quenching process of F-NMAP with DMA is exam-
ined and shown in Fig. 2. It can be seen that the emission
intensity of fluorescence are initially increased and then, de-
creased with gradual increase in concentration of DMA in
ethanol. Meanwhile, the emission peaks show blue-shifted
about 15 nm. In order to go further into the fluorescence
quenching of F-NMAP, the quenching process of F-NMAP
with DMTP is also examined and shown in Fig. 3. As shown
Fig. 3, the variable rule on emission intensity of fluorescence
is the same with the interaction of F-NMAP and DMA, but
the emission peaks show red-shifted about 18 nm with the in-
crease in concentration of DMTP in ethanol. This should be
attributed to the following reasons. Firstly, it is well known
that the performance of conjugated compounds in photoex-
citation and photoinduced charge-transfer (PICT) processes
depends strongly upon their molecular structures and elec-
tronic states. When DMA or DMTP is gradually added into
the solution of F-NMAP, the absorption of DMA or DMTP
3.2. Solvent effects on photoluminescence (PL)
The fluorescence emission spectra of dilute solutions of F-
NMAP are investigated in different solvents and all results are
listed in Table 1. Table 1 shows that the emission spectra of F-
Table 1
The maximum emission peaks and quantum yields of F-NMAP in different
solvents
em
Solvent
Er (30)
ε/n2D0
λ
(nm)
Φs
max
Methanol
Ethanol
Acetonitrile
Ethyl acetate
THF
55.5
51.9
46.0
38.1
37.4
34.6
31.2
24.62
18.03
27.89
4.38
5.39
3.20
366
363
362
360
359
357
353
0.458
0.652
–
0.187
0.297
–
Ether
Cyclohexane
1.42
–

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L. Feng, Z. Chen / Spectrochimica Acta Part A 61 (2005) 2505–2509
Fig. 4. Fluorescence spectra of F-NMAP at different concentrations of
C60. Concentration of F-NMAP, 2.44 × 10−7 mol/L; concentration of C60
Fig. 2. Fluorescence spectra of F-NMAP at different concentrations
of DMA. Concentration of F-NMAP, 2.85 × 10−7 mol/L; concentration
of DMA (mol/L, M): (0) 0.00; (1) 2.69 × 10−5; (2) 6.72 × 10−5; (3)
(mol/L, M): (0) 0.00; (1) 7.94 × 10−8; (2) 1.98 × 10−7; (3) 3.57 × 10−7; (4)
5.16 × 10−7; (5) 7.94 × 10−7
.
1.34 × 10−4; (4) 2.02 × 10−4; (5) 2.69 × 10−4; (6) 3.36 × 10−4
.
slow charge recombination [16]. In the experiment, the in-
teractions of F-NMAP with C60 are examined. The results
are shown in Fig. 4. As we have seen in Fig. 4, ‘0’ is F-
NMAP in concentration (2.44 × 10−7 mol/L) without C60,
‘1–5’ are F-NMAP, in the present, in different concentra-
tions of C60. With the gradual increase in concentration of
C60, the fluorescence of F-NMAP is quenched efficiently and
the process also follows the Stern–Volmer equation (Fig. 5).
The apparent quenching constant is 1.84 × 106 M−1, which
suggests that the strong interactions between F-NMAP and
C60 happen in the excited state. This can be explained by
the following reasons: both F-NMAP and C60 have large ␲-
conjugated system, in which ␲–␲ interactions may change
the configuration of F-NMAP. Moreover, the photoinduced
charge transfer from excited F-NMAP to C60 is rapid.
Upon this charge transfer, the F-NMAP may be dramati-
cally modified because of the strong electron–lattice inter-
action in one-dimensional system. In the system, the pro-
at the excitation and emission of F-NMAP would increase
the fluorescence intensity of F-NMAP. When the concentra-
tion of DMA or DMTP goes beyond a certain scope, the
excess DMA or DMTP units would act as quencher to gradu-
ally quench the fluorescence of F-NMAP. Secondly, DMA
has high ionic potential, which decreases the densities of
electron on F-NMAP and weakens the conjugation extent of
F-NMAP, so the emission peaks are blue-shifted. However,
DMTP has nucleophilic energy, which increases the densi-
ties of electron on F-NMAP and strengthens the conjugation
extent of F-NMAP; therefore, the emission peaks are red-
shifted.
3.5. Interaction between F-NMAP and fullerene C60
Many investigations show that C60 is a good electron ac-
ceptor. It possesses a wide range of physical and chemical
properties. One of the most remarkable properties of C60 is
to induce efficiently, a rapid charge separation and a further
*
cess of charge transfer from ␲ band of the photoexcited
F-NMAP to C60 competes with the radiative emission of
F-NMAP.
Fig. 3. Fluorescence spectra of F-NMAP at different concentrations of
DMTP. Concentration of F-NMAP, 1.46 × 10−7 mol/L; concentration of
DMTP (mol/L, M): (0) 0.00; (1) 6.46 × 10−6; (2) 1.61 × 10−3; (3)
Fig. 5. Dependence of FM0 /FM on concentration of C60. Concentration of
F-NMAP, 2.44 × 10−7 mol/L.
3.22 × 10−3; (4) 4.83 × 10−3; (5) 6.44 × 10−3
.

L. Feng, Z. Chen / Spectrochimica Acta Part A 61 (2005) 2505–2509
2509
Acknowledgements
The present work is 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.
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The carbon nanotubes (CNTs), just like the fullerenes,
belong to an intriguing class of carbon materials. Due to the
unique structures and cavity dimension scale of CNTs, it is
meaningful to study CNTs structure and charge transfer [17].
In this paper, the interactions between F-NMAP and CNTs
are investigated, which is helpful to understand the optical
property of F-NMAP and apply it to LEDs. The experiments
show that the fluorescence of F-NMAP can be quenched by
CNTs. The quenching process of F-NMAP with CNTs is
shown in Fig. 6. Fig. 6 shows that interactions between F-
NMAP and CNTs happens in the excited state, which may be
caused by the photoinduced charge transfer and interactions
of conjugating ␲–␲ system. Further research towards a better
understanding of this action is currently in progress.
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