New fluorene derivatives based on 3,9-dihydrofluoreno[3,2-d]imidazole (FI): Characterization and influence of substituents on photoluminescence

Article abstract of DOI:10.1016/j.jphotochem.2011.01.014

2,3-Diamino-9,9-dioctylfluorene (DADOF), as a new multifunctional intermediate for π conjugated molecules, was efficiently synthesized via a seven-step procedure with an overall yield of 30%. Novel 9,9-dihydro-9,9- dioctyl-2-phenylfluoreno[3,2-d]imidazole (DOFIPh)-type fluorophores with polar substituents were designed and conveniently synthesized from DADOF, and their absorption and fluorescence properties were investigated in solution and in the solid state. The fluorophore DOFIPh exhibits strong blue emission in solid state and fine-tuning of the emission is possible depending on the electronic nature of the substituents.

Full text of DOI:10.1016/j.jphotochem.2011.01.014

Journal of Photochemistry and Photobiology A: Chemistry 219 (2011) 42–49
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Journal of Photochemistry and Photobiology A:
Chemistry
journal homepage: www.elsevier.com/locate/jphotochem
New fluorene derivatives based on 3,9-dihydrofluoreno[3,2-d]imidazole (FI):
Characterization and influence of substituents on photoluminescence
Jian-Guang Guo, Yong-Mei Cui∗, Hai-Xia Lin∗∗, Xiao-Zhen Xie, Hong-Fang Chen
Department of Chemistry, College of Sciences, Shanghai University, 99 Shangda Road, Baoshan District, Shanghai 200444, China
a r t i c l e i n f o
a b s t r a c t
Article history:
2,3-Diamino-9,9-dioctylfluorene (DADOF), as a new multifunctional intermediate for ꢀ conjugated
molecules, was efficiently synthesized via a seven-step procedure with an overall yield of 30%.
Novel 9,9-dihydro-9,9-dioctyl-2-phenylfluoreno[3,2-d]imidazole (DOFIPh)-type fluorophores with polar
substituents were designed and conveniently synthesized from DADOF, and their absorption and fluo-
rescence properties were investigated in solution and in the solid state. The fluorophore DOFIPh exhibits
strong blue emission in solid state and fine-tuning of the emission is possible depending on the electronic
nature of the substituents.
Received 27 September 2010
Received in revised form 12 January 2011
Accepted 21 January 2011
Available online 1 February 2011
Keywords:
Fluorene
Imidazole
© 2011 Elsevier B.V. All rights reserved.
Synthesis
UV absorption
Fluorescence
1. Introduction
unique chemical and physical properties, and emerged as the most
promising blue light-emitting materials for OLEDs [8–12], as well
Organic molecules or polymers with well-defined ꢀ aromatic
backbones have attracted tremendous attention in recent years for
their applications in organic light-emitting diodes (OLEDs) [1,2],
photovoltaic cells [3], plastic lasers [4], and field-effect transistors
(FETs) [5]. Changes in the substitutional groups and substitution
pattern, conjugation, and molecular electronic structure can bring
about very different optical and physical properties for such mate-
rials. To design an organic molecule with a specific application in
mind, knowledge of the material’s structure–property relationship
is necessary. With this understanding, the ability to “tune” a class
of materials to enhance an explicit property can be achieved. Com-
pared to extended ꢀ conjugated polymers, small molecular units
with well-defined conjugation lengths generally possess more pre-
dictable and reproducible properties, are easier to purify, and are
prone to be well characterization. This makes these molecules more
attractive than extended ꢀ-conjugated polymers for investigations
of the structure–property relationship and optimization [6,7].
Due to their rigid planarized oligophenyl unit within the
backbone as well as the possibility of facile functionalization at
the methylene bridge, fluorene-based derivatives have exhibited
as carrier transport materials for FETs [13–15]. Although many
fluorene-based polymers, oligomers have been reported, small-
molecule fluorene derivatives with good thermal stability and
high photoluminescence (PL) efficiency are still rare [16–19]. And
there is a need for exploration and optimization of new organic
luminophores with better properties.
In the search of new luminophores for use in light-emitting
materials, we have given consideration to the benzimidazole
core because of its attractive optical properties. The fact that
the luminescence of this system is greatly influenced by sub-
stituents has also found applications, and phenylbenzo[d]imidazole
unit has been widely used as building blocks due to its
high electron transporting mobility. Among which, 1,3,5-tris(1-
phenylbenzo[d]imidazol-2-yl)benzene (TPBI) is a widely used
electron-transporting and hole-blocking material for fluorescent
and phosphorescent dopants [20–23].
And we are interested in whether replacing the phenyl
ring in benzimidazole luminophore with an even larger yet
flat aromatic system, such as fluorenyl rings, might further
advance its properties. In this paper, we present the ini-
tial expedient synthesis, full characterization of
a series of
fluoreno[3,2-d]imidazole derivatives with various substituents
on the terminal phenyl ring (Fig. 1). The optical absorption
and emission characteristics of this system were examined
for structure–function relationships. Further, single-crystal X-ray
structural determinations was obtained for 2-(4-fluorophenyl)-
∗
Corresponding author. Tel.: +86 21 66132190; fax: +86 21 66134594.
Corresponding author. Tel.: +86 21 66136050; fax: +86 21 66133039.
E-mail addresses: ymcui@shu.edu.cn, ymcui80@gmail.com (Y.-M. Cui),
∗∗
haixialin@staff.shu.edu.cn (H.-X. Lin).
1010-6030/$ – see front matter © 2011 Elsevier B.V. All rights reserved.
doi:10.1016/j.jphotochem.2011.01.014

J.-G. Guo et al. / Journal of Photochemistry and Photobiology A: Chemistry 219 (2011) 42–49
43
NO2
Cl
H
N
H
N
H
N
N
N
N
FIPh-Cl
FIPh-NO2
FI
DOFIPh-Cl
DOFIPh-CH3
DOFIPh
R =
R =
Cl
R =
R =
N
DOFIPh-N(CH3)2
DOFIPh-NO2
H
N
R
N
CH3
NO2
F
F
R
R
R =
R =
R =
R =
DOFIPh-F2
DOFIPh-CF3
CF3
F
DOFIPh-F
Fig. 1. Chemical structure of the fluoreno[3,2-d]imidazole derivatives.
3,9-dihydro-9,9-dioctylfluoreno[3,2-d]imidazole (DOFIPh-F); this
showed the solid state conformation of the imidazole ring. Firstly,
FIPh-Cl and FIPh-NO2 were synthesized, but both showed poor sol-
ubility in common organic solvents. Hence, two octyl groups were
introduced to the C-9 position of the fluorene moiety to increase
solubility as well as to release intermolecular ꢀ–ꢀ stacking. We
focused our attention on DOFIPhs with different substituents on the
terminal phenyl ring to investigate their effects on the absorption
and emission properties of these systems. Detailed study on the
structure–property relationships for these materials can provide
valuable information for molecular design with high performance.
the desired fluoreno[3,2-d]imidazole derivatives in 72–81% yields
(Scheme 2). And all target compounds were isolated and purified
by column chromatography on silica gel with high purity. These
compounds are readily soluble in common organic solvents, such
as CHCl3, CH2Cl2, 1,4-dioxane, tetrahydrofuran (THF), and toluene,
due to the n-octyl substituents, and their molecular structures and
purities were verified by 1H NMR spectroscopy, high resolution
mass spectroscopy, and element analysis.
The ORTEP plot of the solid state conformation and the pack-
ing view of DOFIPh-F are revealed in Fig. 2 [26]. The ORTEP view
of the structure of DOFIPh-F (Fig. 2a) shows the almost planar
arrangement of the fluoreno[3,2-d]imidazole ring together with the
terminal phenyl ring. The fluorene moiety ii forms dihedral angle
of 2.02◦ with the adjacent imidazole ring iii. In contrast, the adja-
cent phenyl ring iv takes a torsion angle of 23.31◦ with respect
to the fluoreno[3,2-d]imidazole moiety. In the crystal lattice, the
molecules are stacked in a head-to-tail manner, forming a non-
coplanar netlike mode of association, as shown in Fig. 2b. Each two
adjacent molecules stack closely through the intermolecular hydro-
2. Results and discussion
The synthetic strategy employed involved the efficient prepa-
ration of the key intermediate 2,3-diamino-9,9-dioctylfluorene
(DADOF) from fluorene. A systematic synthetic route for 2,3,6,7-
tetraamino-9,9-bisalkylfluorene was reported by Qian and co-
workers [24]. And we found that by controlling the reaction time
and the amount of fuming nitric acid, nitration of compound 1
in glacial acetic acid gave mono-nitro compound 2 as the main
product. As shown in Scheme 1, DADOF was successfully syn-
thesized via a 7-step procedure. Dialkylation of fluorene was
accomplished by generation of the fluorenyl anion with KOH in
DMSO and subsequent dioctylation with 1-bromooctane at room
temperature [25]. 9,9-Dioctyl-2-nitrofluorene 2 was prepared in
68% yield by regioselective nitration at 2-position of 1 with fum-
ing nitric acid in glacial AcOH at room temperature for 30 min.
Hydrogenation of 2 with ferrous powder in EtOH/H2O at 90 ◦C
afforded 2-amino-9,9-dioctylfluorene 3 as a yellow solid in 92%
yield. Protection of the amine group of 3 with Ac2O/AcOH, fol-
lowed by regiospecific nitration with fuming nitric acid in AcOH,
gave 2-acetamido-3-nitro-9,9-dioctylfluorene 5 as a brown solid
after column chromatographic purification in total 74% yield by two
steps. Removal of acetyl group of 5, followed by hydrogenation with
ferrous powder in EtOH/H2O at 90 ◦C, provided 2,3-diamino-9,9-
dioctylfluorene (DADOF, 7) in 72% yield (for two steps) as yellow oil.
MS, 1H, and 13C NMR spectroscopic analysis confirmed formation
of this key intermediate.
˚
gen bonding of N· · ·H–N with the distance of 2.092(39) A between
the H–N proton of imidazole ring and the adjacent imino nitrogen
atom. Also, weak intermolecular forces of F· · ·H–C with the distance
˚
of 2.715(3) A between the fluorine atom and the adjacent H–C pro-
ton of the terminal n-octyl side chain was observed, as shown in
Fig. 2c and d.
The photophysical properties of the compounds were exam-
ined by UV–vis and photoluminescent (PL) spectra in dilute CH2Cl2,
DMSO solutions and in the solid films, as shown in Figs. 3 and 4. Both
the photophysical data in these two solvents of different polarity
and the PL spectra data of the compounds in thin films are listed
in Table 1. In order to study the substituent effect on the optical
properties, a series of compounds with various polar groups (i.e.,
X = H, F, Cl, CH3, CF3, NO2, and NMe2) substituted on the phenyl ring
were studied. Among these polar groups, some are known as strong
ꢀ-acceptors (i.e., X = NO2), others are known as intermediate (i.e.,
X = F, and Cl), besides being classified as electron-withdrawing (i.e.,
X = F, Cl, CF3, and NO2) or electron-donating groups (i.e., X = CH3,
and NMe2). The results indicated that the photophysical behavior
of this electron-deficient heterocyclic system was sensitive to the
electronic factors of the substituents.
From the key intermediate 7, all target compounds can be
obtained by one-step, concise synthetic procedure. Condensation of
7 with the corresponding aldehydes in dioxane at 95 ◦C for 8 h gave
As it can be observed in Fig. 3a, the UV–vis absorption spectra of
all compounds in CH2Cl2 were very similar in shape, compound

44
J.-G. Guo et al. / Journal of Photochemistry and Photobiology A: Chemistry 219 (2011) 42–49
1-bromooctane,
fuming nitric acid
NO2
(CH2)7CH3
KOH, DMSO,
r.t. 5 h
AcOH, r.t. 30 min
68%
(CH2)7CH3
H3C(H2C)7
H3C(H2C)7
91%
1
2
Fe powder
NH2
AcOH, Ac2O
NHAc
fuming nitric acid
EtOH/H2O
90 oC, 30 min
92%
r.t. 6 h
87%
AcOH, r.t. 30 min
85%
H3C(H2C)7
(CH2)7CH3
H3C(H2C)7
(CH2)7CH3
3
4
NH2
NH2
NO2
NO2
NHAc
70% H2SO4
90 oC, 5 h
88%
Fe powder
EtOH/H2O
NH2
H3C(H2C)7
(CH2)7CH3
H3C(H2C)7
(CH2)7CH3
90 oC, 30 min
82%
H3C(H2C)7
(CH2)7CH3
5
6
DADOF, 7
Scheme 1. Synthesis of 2,3-diamino-9,9-dioctylfluorene 7 (DADOF).
H
X
N
NH2
NH2
N
X
dioxane, 95 oC
+
OHC
H3C(H2C)7
DOFIPhs
X= H, F, Cl, CH3, CF3, NO2, NMe2
(CH2)7CH3
H3C(H2C)7
(CH2)7CH3
8 h
72-81% yields
7
Scheme 2. Synthesis of DOFIPh and its derivatives.
DOFIPh (X = H) exhibited the absorption maximum at 340 nm,
which could be ascribed to the ꢀ–ꢀ* transition of the molec-
ular backbone. The UV–vis absorption maxima of compounds
DOFIPh, DOFIPh-CH3, DOFIPh-F and DOFIPh-F2 were almost the
same. The UV–vis absorption maxima of DOFIPh-Cl, DOFIPh-CF3
and DOFIPh-NMe2 were red-shifted by 5, 8 and 18 nm, respec-
tively, relative to that of DOFIPh, and the enormous red shift of
51 nm as observed in DOFIPh-NO2 with a broad and featureless
absorption band. The effect of the substituent on the absorption
properties is not clearly seen. This suggests that the electronic prop-
erties of the substituents might not play an important role in the
UV–vis absorption spectra. For evaluating the solvatochromism of
Fig. 2. Crystal structure of DOFIPh-F: (a) ORTEP drawing, (b) a view of the molecular packing structure, (c) a side view, and (d) a top view of the pair of moleculars.

J.-G. Guo et al. / Journal of Photochemistry and Photobiology A: Chemistry 219 (2011) 42–49
45
Table 1
Thermal and optical properties of the compounds.
Compound
ꢁabs (nm)a
ꢁem (nm)b
c
CH2Cl2
DMSO
CH2Cl2
DMSO
film
ꢂFL
DOFIPh
340
341
358
338
345
341
348
391
342, 356
342, 357
361
340, 354
346, 360
329
372, 385
367, 385
392, 412
366, 383
393
373, 386
368, 384
414
368, 384
395
389, 442
388, 443
483
388, 433
426
391, 417
398, 427
526
0.50
0.41
0.45
0.29
0.45
0.48
0.54
0.15
DOFIPh-CH3
DOFIPh-NMe2
DOFIPh-F
DOFIPh-Cl
DOFIPh-F2
DOFIPh-CF3
DOFIPh-NO2
388
416
421
393
427
467
359
400
a
UV–vis absorption wavelengths in dichloromethane or in DMSO at room temperature.
Fluorescence wavelengths in dichloromethane, DMSO or in thin neat films at room temperature.
Fluorescence quantum yields, measured in CH2Cl2 solution using a 0.2 M H2SO4 solution of quinine sulfate (ꢂFL = 0.55) as a reference.
b
c
the fluoreno[3,2-d]imidazoles, their UV–vis spectra were measured
in DMSO solutions. As shown in Fig. 3b, all derivatives showed
almost the same UV–vis spectra regardless of solvent polarity. The
absorption spectra underwent small red shifts on going from the
CH2Cl2 solutions to the DMSO solutions, and their relative order
of the values of absorption maxima (ꢁmax) retained the same as
observed in solutions, except compound DOFIPh-F2 (Table 1). These
shifts of the UV–vis absorption wavelengths might be affected due
to the charge transfer molecule whose energy in ground state
changes by solvents. And new absorption bands at 356, 357, 354
and 360 nm for compounds DOFIPh, DOFIPh-CH3, DOFIPh-F and
DOFIPh-Cl were observed in DMSO, respectively, presumably due
to the accelerated CT complex formation in the ground state in polar
solvent.
Fig. 4 shows the photoluminescence (PL) spectra recorded upon
excitation at absorption maximum at room temperature. In CH2Cl2
solution, the fluorescence spectra of DOFIPh showed two peaks at
372 and 385 nm (Fig. 4a) and the fluorescence quantum yield is
0.50, which is comparable to that of quinine sulfate (ꢂFL = 0.55).
The fluorescence spectra of compounds DOFIPh-CH3 and DOFIPh-
F were very similar to those of DOFIPh, showing two peaks at
ca. 367 and 384 nm. The fluorescence maxima of DOFIPh-Cl and
DOFIPh-F2 were slightly red-shifted relative to those of DOFIPh.
It is interesting to note that the fluorescence maxima of DOFIPh-
NMe2, DOFIPh-CF3 and DOFIPh-NO2, relative to those of DOFIPh,
were red-shifted by 27, 30 and 36 nm, respectively, and compound
DOFIPh-NO2 fluoresced in dichloromethane with emission peaks
at ca. 421 nm, probably due to the elongation of the conjugation
length and the increased charge-transfer character induced by the
fluoroalkyl or nitro groups. All the synthesized compounds were
moderate fluorescent in CH2Cl2 solution with fluorescence quan-
tum yields in the range of 0.15–0.54. It should be noted that the
fluorescence quantum yield of DOFIPh-NO2 (0.15) is lower than the
yields of the other synthesized ꢀ-extended fluorenes. In general,
the fluorescence quantum yield of a fluorophore containing nitro
groups is extremely low because of the decrease in the radiative
rate and the increase in the internal conversion rate of an excited
state fluorophore [27]. However, this fluorescence quantum yield
of DOFIPh-NO2 is exceptionally higher than the yields of other gen-
eral nitro-group-containing fluorophores (ꢂFL < 0.01) [28,29]. Next,
fluorescence spectra for DOFIPhs were measured in DMSO for certi-
fying the influence of solvent polarity on their emission. As shown
in Fig. 4b, most compounds were slightly red-shifted relative to
those in CH2Cl2. DOFIPh-NMe2 showed the disappearance of its
vibronic band. In the case of DOFIPh-NO2, the difference in the shift
spans ca. 46 nm from CH2Cl2 to DMSO. Such large shift observed
for DOFIPh-NO2 in polar solvent may result from the difference in
the dipole moments between the delocalized ground state and the
highly localized excited one.
PL spectra in the solid state were carried out on films spin-coated
onto quartz from chloroform solution. By comparison with the
dilute CH2Cl2 solutions, the emission spectra of all compounds in
solid states showed red-shifts to longer wavelengths by 11–105 nm
(Fig. 4c). The red-shifts of the emission observed in the solid state
were probably due to the rigid fluoreno[3,2-d]imidazole group and
its strong intermolecular forces, which drove the molecules to pack
at high density, restricted the molecular rotation and increased the
ꢀ-conjugation significantly, in turn resulting in the red-shifts. In
the solid state, the fluorescence maxima of unsubstituted DOFIPh
were red-shifted by ca. 57 nm relative to those in CH2Cl2 solution,
showing two peaks at 389 and 442 nm. Substitution with methyl
group (DOFIPh-CH3) produces a small red-shift in the emission and
Fig. 3. Normalized absorption spectra of DOFIPhs (1 × 10−5 M) recorded in CH2Cl2
solutions (a) and in DMSO solutions (b) at room temperature.

46
J.-G. Guo et al. / Journal of Photochemistry and Photobiology A: Chemistry 219 (2011) 42–49
group is also known as good ꢀ-acceptor, and has a more pla-
nar structure (i.e., sp2 hybrid orbital). The bathochromic shift in
PL emission maximum might be attributed to two factors. Elec-
tronically, a conjugative interaction over the entire molecule was
better achieved between the polar substituent and the other side
of fluoreno[3,2-d]imidazole, and also a better packing arrangement
due to a more overall molecular planar structure may be achieved
in the solid state. Through control of the substituents of DOFIPhs, a
broad range of emissions in the visible region can be achieved.
3. Conclusion
In summary, 2,3-diamino-9,9-dioctylfluorene (DADOF), as a
new multifunctional intermediate for ꢀ conjugated molecules,
was efficiently synthesized via
a seven-step procedure with
an overall yield of 30%. And novel 3,9-dihydro-9,9-dioctyl-2-
phenyl fluoreno[3,2-d]imidazole (DOFIPh)-type fluorophores with
polar substituents were designed and conveniently synthesized,
and their absorption and fluorescence properties were inves-
tigated in solution and in the solid state. The DOFIPhs were
synthesized by condensation of the key intermediate 2,3-biamino-
9,9-bioctylfluorene with aldehydes under very mild conditions,
which make it possible to incorporate a diverse range of sub-
stituents in the DOFIPh core. The fluorophore DOFIPh exhibits
strong blue emission in solid state and fine-tuning of the emission
is possible depending on the electronic nature of the substituents.
Further research regarding the incorporation of these systems
usable both as organic light-emitting diodes and as fluorescent
probes is under way in our laboratory.
4. Experimental
4.1. General
Commercially available reagents were purchased and were used
without further purification unless otherwise mentioned. 1H NMR
and 13C NMR spectra were recorded on a Bruker Avance (500 MHz)
spectrometer in CDCl3 or DMSO-d6, unless otherwise noted. Chem-
ical shifts are reported in parts per million (ppm) and coupling
constants (J) are reported in Hertz (Hz). Coupling patterns are
described by abbreviations: s (singlet), d (doublet), t (triplet), m
(multiplet), br (broad). Chemical shifts in CDCl3 were reported in
the scale relative to CHCl3 (7.26 ppm) for 1H NMR, and to CDCl3
(77.16 ppm) for 13C NMR, as internal references. The center line
of the multiplets of DMSO-d6 was defined as 2.50 for 1H NMR.
Mass spectra were recorded using an EI source (Agilent 5975N
instrument). Silica gel plate GF254 was used for thin layer chro-
matography (TLC) and silica gel H or 300–400 mesh was used for
flash column chromatography. Melting points were measured on
a Digital Melting Point Apparatus without correction. Yields are
shown in terms of those of isolated pure materials. The absorp-
tion and fluorescence spectra were recorded using a UV-2501Pc
spectrophotometer and a RF-5301 fluorescence spectrophotome-
ter. High-resolution mass spectra (HR-MS) were recorded on an
IonSpec 4.7 Tesla FTMS instrument. Elemental analysis was per-
formed on an Elementar Vario EL (Germany) instrument.
Fig. 4. Normalized fluorescence spectra of DOFIPhs recorded in CH2Cl2 solutions
(5 × 10−7 M, (a)), in DMSO solutions (5 × 10−7 M, (b)) and in thin neat films (c) excited
at the each absorption maximum at room temperature.
shows blue PL (ꢁmax = 443 nm). Halogenation (DOFIPh-F, DOFIPh-
Cl, DOFIPh-F2) produces a noticeable blue-shift in their solid-state
PL emission (ꢁmax = 433, 426 and 417 nm, respectively). Also, a sim-
ilar blue-shift is seen in the solid PL emission of p-CF3 substituted
derivative DOFIPh-CF3, and blue PL (ꢁmax = 427 nm) was obtained.
Derivative DOFIPh-NMe2 with donor substituent (NMe2) showed
blue-green emission, with a PL emission maximum at 483 nm.
Interestingly, compound DOFIPh-NO2 with strong ꢀ-acceptor sub-
stituent exhibited a larger red shift (105 nm) than the other DOFIPh
derivatives, and showed green PL (ꢁmax = 526 nm). The polar nitro
4.2. Synthesis
4.2.1. 9,9-Bioctylfluorene (1)
To a solution of fluorene (4.15 g, 0.025 mol), potassium hydrox-
ide (5.6 g, 0.1 mol) in DMSO (50 mL), was added 1-bromooctane
(9.65 g, 0.05 mol) at room temperature and the reaction mixture
was allowed to stir for 5 h. The reaction mixture was poured
into water, and then the mixture was extracted with AcOEt.

J.-G. Guo et al. / Journal of Photochemistry and Photobiology A: Chemistry 219 (2011) 42–49
47
The combined organic layer was washed with brine, dried over
MgSO4, filtered, and then the solvent was evaporated in vacuum.
The residue was purified by flash column chromatography using
petroleum ether as eluent to afford 1 (8.95 g, yield 91%) as light
yellow oil. 1H NMR (500 MHz, CDCl3): ı ppm 7.72 (d, J = 7.5 Hz, 2H),
7.36–7.29 (m, 6H), 1.99–1.96 (m, 4H), 1.24–1.06 (m, 20H), 0.84 (t,
J = 7.0 Hz, 6H), 0.65–0.63 (m, 4H).
stirred for 5 h. The resulting solution was poured into water
(20 mL). After cooling, the red precipitate was filtered under
reduced pressure. The crude solid was purified by flash column
chromatography using petroleum ether:AcOEt (5:1) as eluent to
afford 6 (2.4 g, yield 88%, Mp = 156–157 ◦C) as a dark red solid.
1H NMR (500 MHz, CDCl3): ı ppm 8.41 (s, 1H), 7.64 (d, J = 7.0 Hz,
1H), 7.34–7.26 (m, 3H), 6.76 (s, 1H), 6.29 (br, 2H), 1.98–1.84 (m,
4H), 1.22–1.04 (m, 20H), 0.82 (t, J = 7.0 Hz, 6H), 0.67–0.58 (m,
4H).
4.2.2. 2-Nitro-9,9-bioctylfluorene (2)
To a solution of 9,9-bioctylfluorene 1 (7.8 g, 20 mmol) in glacial
acetic acid (30 mL) was added fuming nitric acid (8 mL) dropwise
at 0 ◦C. After the addition of nitric acid, the resulting solution was
allowed to warm to room temperature and was stirred for 30 min.
Then the reaction mixture was poured into water (20 mL). The
yellow oil was extracted with AcOEt. The combined organic layer
was purified by flash column chromatography using petroleum
ether:AcOEt (20:1) as eluent to afford 2 (5.9 g, yield 68%) as yel-
low oil. 1H NMR (500 MHz, CDCl3): ı ppm 8.27 (dd, J = 8.0, 2.0 Hz,
1H), 8.22 (d, J = 2.0 Hz, 1H), 7.81–7.78 (m, 2H), 7.45–7.38 (m, 3H),
2.03 (m, 4H), 1.26–1.03 (m, 20H), 0.81 (t, J = 7.0 Hz, 6H), 0.62–0.53
(m, 4H).
4.2.7. 2,3-Biamino-9,9-bioctylfluorene (7)
A
mixture of ferrous powder (560 mg, 10 mmol) in H2O
(20 mL) was heated to 90 ◦C. Then concentrated hydrochloric
acid (8 mL) was added dropwise, after that, 2-amino-3-nitro-9,9-
bioctylfluorene 6 (450 mg, 1 mmol) dissolved in ethanol (20 mL)
was added to the mixture. The mixture was stirred vigor-
ously for 30 min. The reaction mixture was poured into water,
and then the mixture was extracted with AcOEt. The com-
bined organic layer was evaporated in vacuum. The residue
was purified by flash column chromatography using petroleum
ether:AcOEt (3:1) as eluent to afford 7 (344 mg, yield 82%) as
yellow oil. 1H NMR (500 MHz, CDCl3): ı ppm 7.40 (d, J = 8.0 Hz,
1H), 7.16 (m, 2H), 7.08 (t, J = 7.0 Hz, 1H), 6.96 (s, 1H), 6.58
(s, 1H), 3.42 (br, 4H), 1.81–1.74 (m, 4H), 1.13–0.95 (m, 20H),
0.74 (t, J = 7.0 Hz, 6H), 0.60–0.52 (m, 4H); 13C NMR (125 MHz,
CDCl3): ı ppm 150.6, 143.9, 141.8, 134.9, 133.7, 133.2, 126.6,
125.4, 122.6, 118.4, 111.3, 108.6, 54.5, 40.7, 31.9, 30.3, 29.8, 29.4,
23.9, 22.7, 14.2. MS (EI) m/z = 420.4 (M+), calcd for C29H44N2,
M = 420.4.
4.2.3. 2-Amino-9,9-bioctylfluorene (3)
A mixture of ferrous powder (3.3 g, 58 mmol) in H2O (30 mL)
was heated to 90 ◦C. Concentrated hydrochloric acid (15 mL) was
added slowly. Then 2-nitro-9,9-bioctylfluorene 2 (4.35 g, 10 mmol)
dissolved in ethanol (30 mL) was added to the mixture, and was
stirred vigorously for 30 min. The reaction mixture was filtered and
washed with H2O. The crude solid was purified by flash column
chromatography using petroleum ether:AcOEt (10:1) as eluent
to afford 3 (3.7 g, yield 92%, Mp = 58–60 ◦C) as a white solid. 1H
NMR (500 MHz, DMSO-d6): ı ppm 7.49 (d, J = 7.5 Hz, 1H), 7.40 (d,
J = 8.0 Hz, 1H), 7.25 (d, J = 7.0 Hz, 1H), 7.18 (t, J = 7.5 Hz, 1H), 7.08
(t, J = 7.0 Hz, 1H), 6.56 (d, J = 2.0 Hz, 1H), 6.51 (dd, J = 8.0, 2.0 Hz,
1H), 5.19 (br, 2H), 1.91–1.741 (m, 4H), 1.18–0.98 (m, 20H), 0.78
(t, J = 7.0 Hz, 6H), 0.57–0.45 (m, 4H).
4.2.8. General procedure for synthesis of FIPh-Cl, FIPh-NO2 and
DOFIPhs
A
mixture of the corresponding aldehyde (1 mmol) and
2,3-biamino-9,9-bioctylfluorene (420 mg, 1 mmol) or 2,3-
7
biaminofluorene (196 mg, 1 mmol) in dioxane was refluxed for 8 h.
The solvent was removed under vacuum and the residue was puri-
fied by flash column chromatography using petroleum ether/ethyl
acetate as eluent to afford the desired compounds.
4.2.4. 2-Acetamido-9,9-bioctylfluorene (4)
To a solution of 2-amino-9,9-bioctylfluorene 3 (3.64 g, 9 mmol)
in glacial acetic acid (30 mL) was added acetic anhydride (20 mL)
dropwise at room temperature for 6 h. Then H2O (40 mL) was
slowly added. And the mixture was filtered and washed with water.
The crude solid was purified by flash column chromatography using
petroleum ether:AcOEt (5:1) as eluent to afford 4 (3.5 g, yield 87%,
Mp = 147–148 ◦C) as a light yellow solid. 1H NMR (500 MHz, CDCl3):
ı ppm 7.63–7.61 (m, 2H), 7.55 (d, J = 1.5 Hz, 1H), 7.44 (dd, J = 8.0,
1.5 Hz, 1H), 7.31–7.24 (m, 4H), 2.21 (s, 3H), 1.94–1.90 (m, 4H),
1.18–1.02 (m, 20H), 0.81 (t, J = 7.0 Hz, 6H), 0.61–0.57 (m, 4H).
4.2.9. 2-(4-Chlorophenyl)-3,9-dihydrofluoreno[3,2-d]imidazole
(FIPh-Cl)
White solid, yield 72%. Mp 222–224 ◦C. 1H NMR (500 MHz,
DMSO-d6): ı ppm 13.07 (br, 1H), 8.21 (d, J = 8.5 Hz, 2H), 8.05 (s,
1H), 7.95 (d, J = 7.5 Hz, 1H), 7.75 (s, 1H), 7.62 (d, J = 8.5 Hz, 2H), 7.54
(d, J = 7.5 Hz, 1H), 7.37 (t, J = 7.5 Hz, 1H), 7.27 (m, 1H), 3.98 (s, 2H).
MS (EI) m/z = 316.1 (M+), calcd for C20H1335ClN2, M = 316.1.
4.2.10. 2-(4-Nitrophenyl)-3,9-dihydrofluoreno[3,2-d]imidazole
(FIPh-NO2)
4.2.5. 2-Acetamido-3-nitro-9,9-bioctylfluorene (5)
Yellow solid, yield 80%. Mp 232–234 ◦C. 1H NMR (500 MHz,
DMSO-d6): ı ppm 13.30 (br, 1H), 8.44–8.39 (m, 4H), 8.09 (s, 1H),
7.98 (d, J = 7.5 Hz, 1H), 7.80 (s, 1H), 7.55 (d, J = 7.0 Hz, 1H), 7.38 (t,
J = 7.0 Hz, 1H), 7.28 (t, J = 7.0 Hz, 1H), 4.01 (s, 2H). MS (EI) m/z = 327.2
(M+), calcd for C20H13N3O2, M = 327.1.
To
a solution of 2-acetamido-9,9-bioctylfluorene 4 (3.1 g,
7 mmol) in glacial acetic acid (30 mL) was added fuming nitric acid
(3 mL) dropwise at room temperature. And the resulting solution
was stirred for 30 min. Then the reaction mixture was poured into
20 mL water. The solid was filtered under reduced pressure, and
the separated solid was washed several times with water. The
crude solid was purified by flash column chromatography using
petroleum ether:AcOEt (10:1) as eluent to afford 5 (2.9 g, yield 85%,
Mp = 67–68 ◦C) as a brown solid. 1H NMR (500 MHz,CDCl3): ı ppm
10.5 (s,1H), 8.81 (s, 1H), 8.49 (s, 1H), 7.72–7.69 (m, 1H), 7.39–7.33
(m, 3H), 2.33 (s, 3H), 2.04–1.94 (m, 4H), 1.21–1.02 (m, 20H), 0.80 (t,
J = 7.0 Hz, 6H), 0.61–0.54 (m, 4H).
4.2.11. 2-(4-Fluorophenyl)-9,9-dioctyl-3,9-dihydrofluoreno[3,2-
d]imidazole
(DOFIPh-F)
Light yellow solid, yield 72%. Mp 177–179 ◦C. 1H NMR (500 MHz,
CDCl3): ı ppm 8.06 (dd, J = 8.5, 5.0 Hz, 2H), 7.74 (s, 1H), 7.53 (dd,
J = 5.5, 3.0 Hz, 1H), 7.47 (s, 1H), 7.23 (dd, J = 6.5, 2.0 Hz, 1H), 7.19–7.17
(m, 2H), 6.99 (t, J = 8.5 Hz, 2H), 1.90–1.83 (m, 4H), 1.08–0.91 (m,
20H), 0.70 (t, J = 7.0 Hz, 6H), 0.55–0.53 (m, 4H). HR-MS: calcd for
C36H45FN2 ([M+H]+), 525.3645; found, 525.3644. Anal. calcd for
4.2.6. 2-Amino-3-nitro-9,9-bioctylfluorene (6)
C
5.16.
36H45FN2: C, 82.40; H, 8.64; N, 5.34. Found: C, 82.48; H, 8.53; N,
A mixture of 2-acetamido-3-dinitro-9,9-bioctyl-fluorene 5 (3 g,
6 mmol) in 70% sulfuric acid (20 mL) was heated to 90 ◦C and

48
J.-G. Guo et al. / Journal of Photochemistry and Photobiology A: Chemistry 219 (2011) 42–49
4.2.12. 2-(4-Chlorophenyl)-9,9-dioctyl-3,9-dihydrofluoreno[3,2-
d]imidazole
C36H44F2N2: C, 79.67; H, 8.17; N, 5.16. Found: C, 79.69; H, 8.36;
N, 4.96.
(DOFIPh-Cl)
White solid, yield 77%. Mp 195–196 ◦C. 1H NMR (500 MHz,
CDCl3): ı ppm 8.05 (d, J = 8.5 Hz, 2H), 7.83 (s, 1H), 7.63 (dd, J = 5.5,
2.5 Hz, 1H), 7.59 (s, 1H), 7.36 (d, J = 8.5 Hz, 2H), 7.33–7.30 (m, 1H),
7.29–7.27 (m, 2H), 2.02–1.91 (m, 4H), 1.18–0.99 (m, 20H), 0.79 (t,
J = 7.0 Hz, 6H), 0.66–0.59 (m, 4H). HR-MS: calcd for C36H4535ClN2
([M+H]+), 541.3349; found, 541.3344. Anal. calcd for C36H45ClN2:
C, 79.89; H, 8.38; N, 5.18. Found: C, 79.61; H, 8.18; N, 4.96.
4.2.18. 9,9-Dioctyl-2-(4-(trifluoromethyl)phenyl)-3,9-
dihydrofluoreno[3,2-d]imidazole
(DOFIPh-CF3)
Yellow solid, yield 80%. Mp 183–186 ◦C. 1H NMR (500 MHz,
CDCl3): ı ppm 8.20 (d, J = 8.0 Hz, 2H), 7.89 (s, 1H), 7.69 (s, 1H),
7.64 (dd, J = 5.0, 3.0 Hz, 1H), 7.60 (d, J = 8.0 Hz, 2H), 7.36–7.32 (m,
1H), 7.31–7.28 (m, 2H), 2.02–1.97 (m, 4H), 1.19–1.01 (m, 20H), 0.79
(t, J = 7.0 Hz, 6H), 0.66–0.62 (m, 4H). HR-MS: calcd for C37H45F3N2
([M+H]+), 575.3613; found, 575.3615. Anal. calcd for C37H45F3N2:
C, 77.32; H, 7.89; N, 4.87. Found: C, 77.44; H, 7.72; N, 4.75.
4.2.13.
9,9-Dioctyl-2-p-tolyl-3,9-dihydrofluoreno[3,2-d]imidazole
(DOFIPh-CH3)
Light yellow solid, yield 76%. Mp 160–162 ◦C. 1H NMR (500 MHz,
CDCl3): ı ppm 7.97 (d, J = 8.0 Hz, 2H), 7.68 (s, 1H), 7.52 (d, J = 6.5 Hz,
1H), 7.47 (s, 1H), 7.23–7.20 (m, 1H), 7.19–7.14 (m, 4H), 2.27 (s,
3H), 1.89–1.84 (m, 4H), 1.10–0.91 (m, 20H), 0.70 (t, J = 7.0 Hz, 6H),
0.59–0.50 (m,4H). HR-MS: calcd for C37H48N2 ([M+H]+), 521.3895;
found, 521.3887. Anal. calcd for C37H48N2: C, 85.33; H, 9.29; N, 5.38.
Found: C, 85.05; H, 9.12; N, 5.29.
Acknowledgements
The authors are grateful for support from the National Natu-
ral Science Foundation of China (Project No. 30672506), Leading
Academic Discipline Project of Shanghai Municipal Education Com-
mission (Project No. J50102), and Shanghai Pujiang Program (No.
10PJ1403700).
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9,9-Dioctyl-2-phenyl-3,9-dihydrofluoreno[3,2-d]imidazole
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Light yellow solid, yield 81%. Mp 138–140 ◦C. 1H NMR (500 MHz,
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N,N-dimethylbenzenamine
(DOFIPh-N(CH3)2)
Yellow solid, yield 75%. Mp 128–130 ◦C. 1H NMR (500 MHz,
CDCl3): ı ppm 7.91 (d, J = 9.0 Hz, 2H), 7.68 (s, 1H), 7.56 (d, J = 7.0 Hz,
1H), 7.46 (s, 1H), 7.23–7.14 (m, 3H), 6.67 (d, J = 9.0 Hz, 2H), 2.92 (s,
6H), 1.89 (t, J = 8.0 Hz, 4H), 1.10–0.92 (m, 20H), 0.72 (t, J = 7.0 Hz, 6H),
0.58–0.51 (m, 4H). HR-MS: calcd for C38H51N3 ([M+H]+), 550.4161;
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Found: C, 82.75; H, 9.27; N, 7.63.
4.2.17. 2-(2,6-Difluorophenyl)-9,9-dioctyl-3,9-
dihydrofluoreno[3,2-d]imidazole
(DOFIPh-F2)
Yellow solid, yield 74%. Mp 139–141 ◦C. 1H NMR (500 MHz,
CDCl3): ı ppm 12.49 (br, 1H), 7.86 (s, 1H), 7.67 (d, J = 6.5 Hz, 1H),
7.59 (s, 1H), 7.37 (d, J = 7.0 Hz, 1H), 7.34–7.29 (m, 2H), 7.26 (t,
J = 6.5 Hz, 1H), 6.94 (t, J = 8.5 Hz, 2H), 2.02–2.00 (m, 4H), 1.25–1.08
(m, 20H), 0.84 (t, J = 7.0 Hz, 6H), 0.70 (m, 4H). HR-MS: calcd for
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space group P21/c, Z = 4, Dcalc = 1.061 g cm−3, a = 32.323(13), b = 10.430(4),
3
˛ = 90◦,
ˇ = 90.923(7)◦,
ꢃ = 90◦,
V = 3284(2) A ,
Z = 4,
˚
˚
c = 9.742(4) A,
ꢄ = 0.065 mm−1
,
T = 293(2) K, 13,502 total and 5898 independent
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a
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