Synthesis and photoelectric properties of novel indeno[2,1-a]phenalene- based derivatives

Article abstract of DOI:10.1016/j.dyepig.2013.01.012

A series of novel indeno[2,1-a]phenalene derivatives 4a-j including electron-donating or electron-withdrawing groups were prepared by Pd-catalyzed Sonogashira-Hagihara reaction of 7-iodo-12-phenylindeno[2,1-a]phenalene with various arylacetylene. Photoele

Full text of DOI:10.1016/j.dyepig.2013.01.012

Dyes and Pigments 97 (2013) 389e396
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Dyes and Pigments
journal homepage: www.elsevier.com/locate/dyepig
Synthesis and photoelectric properties of novel indeno[2,1-a]phenalene-based
derivatives
*
*
Duanqin Li, Miaochang Liu, Jiuxi Chen, Jian Lan, Xiaobo Huang , Huayue Wu
College of Chemistry and Materials Engineering, Wenzhou University, Wenzhou 325035, China
a r t i c l e i n f o
a b s t r a c t
Article history:
A series of novel indeno[2,1-a]phenalene derivatives 4aej including electron-donating or electron-
withdrawing groups were prepared by Pd-catalyzed SonogashiraeHagihara reaction of 7-iodo-12-
phenylindeno[2,1-a]phenalene with various arylacetylene. Photoelectric properties of these com-
pounds were investigated by UVevis absorption and fluorescence. The fluorescent emission of 4d con-
taining dimethyl amino group is correlated with solvent polarity and environmental acidity, which
indicates that this kind of compound can be used as solvent polarity sensor and pH sensor. In addition,
the band gaps of these indeno[2,1-a]phenalene derivatives can be tuned in the range 1.78e2.09 eV by
using different substituted groups. These findings indicate that indeno[2,1-a]phenalene-based molecule
can be developed as an excellent fluorophore for optoelectronic material applications.
Received 19 December 2012
Received in revised form
8 January 2013
Accepted 11 January 2013
Available online 31 January 2013
Keywords:
Indeno[2,1-a]phenalene
Photoelectric properties
Fluorescence
Ó 2013 Elsevier Ltd. All rights reserved.
Solvent effect
Solvent polarity sensor
pH sensor
1. Introduction
group [7] reported the synthesis of novel indeno[2,1-a]phenalene
derivatives by iodine-mediated electrophilic cyclizations of differ-
Over the past ten years, fluorescent chemosensors have attrac-
ted much interest owing to their high sensitivity, selectivity,
adaptability and ease of measurement. And a large number of
functional organic materials have been designed and used as flu-
orescent chemosensors for cations [1], anions [2], chiral molecules
detection [3], and they also can be applied in biological and medical
study [4]. Polycyclic aromatic hydrocarbons (PAHs) play a very
important position in the design and synthesis field of fluorescent
sensor due to strong and stable fluorescence, but so far, the most
commonly used PAH fluorophores are a few structure simple PAHs,
such as naphthalene, anthracene, pyrene, etc, which are often
limited at short excitation and emission wavelengths (mostly in the
ultraviolet or blue light region) [1a,1ced,2a,3a]. Therefore, the
design and development of novel PAH fluorophores is very
necessary.
ent 1,8-dialkynylnaphthalenes, respectively. To the best of our
knowledge, there has been no report on the synthesis of indeno
[2,1-a]phenalene-based derivatives incorporating either electron
donors or electron acceptors by a carbonecarbon triple bond. As
a further extension of our research on the design of new polycyclic
aromatic hydrocarbons (PAHs) for photoelectric materials, herein,
we described a series of PAH molecules 4aej based on indeno[2,1-
a]phenalene skeleton by introducing appropriate electron donors
and acceptors via an ethynyl linkage and investigated their pho-
tophysical, electrochemical properties, and structure-property
relationship.
2. Experimental part
2.1. Materials
Arylene ethynylene derivatives with two parallel triple bonds
became useful precursors for the synthesis of PAHs through an
electrophilic, thermal cyclization reaction or a transition-metal-
catalyzed annulation reaction [5]. Recently, our group [6] and Lu’
All solvents and reagents were commercially available and
analytical-reagent-grade. THF and Et3N were purified by distillation
from sodium in the presence of benzophenone. 1,8-
Diiodonaphthalene 1 could be synthesized from the starting ma-
terial 1,8-diaminenaphthalene according to reported literature [8].
1,8-Diaminenaphthalene and various arylacetylene were pur-
chased from Aldrich and directly used without further purification.
* Corresponding authors. Tel./fax: þ86 577 88368280.
E-mail addresses: xiaobhuang@wzu.edu.cn (X. Huang), huayuewu@wzu.edu.cn
(H. Wu).
0143-7208/$ e see front matter Ó 2013 Elsevier Ltd. All rights reserved.
http://dx.doi.org/10.1016/j.dyepig.2013.01.012

390
D. Li et al. / Dyes and Pigments 97 (2013) 389e396
2.2. Measurements
129.7, 129.0, 128.7, 128.6, 128.2, 128.0, 127.8, 127.5, 126.5, 126.4,
126.3, 125.4, 125.0, 123.6, 120.4, 119.7, 115.2, 114.4, 114.3, 102.1, 85.6,
55.5; MS (EI): m/z: 458.2 [Mþ]; Elemental analysis: calcd. for
C35H22O: C, 91.68; H, 4.84, found C, 91.61; H, 4.81.
Melting points were recorded on a Buchi Melting Point B-540
(uncorrected). The 1H NMR and 13C NMR spectra were recorded in
solution of CDCl3 on Bruker DPX 300 or DRX 500 NMR spec-
trometer with tetramethylsilane (TMS) as the internal standard.
The chemical shift was recorded in ppm and the following abbre-
viations were used to explain the multiplicities: s ¼ singlet,
d ¼ doublet, m ¼ multiplet, br ¼ broad. EI mass spectra were
recorded on Agilent 5975C DIP/MS mass spectrometer. C, H and N
of elemental analyses were performed on an Elementar Vario MI-
CRO analyzer. UVevis absorption was recorded on Shimadzu UV-
1700 spectrometer and fluorescence spectra were recorded on
a RF-5301PC fluorometer. The electrochemical measurements were
carried out in anhydrous CH2Cl2 with 0.1 M tetrabutylammonium
hexafluorophosphate (Bu4NPF6) as the supporting electrolyte at
a scan rate of 0.02 V/s at room temperature under the protection of
nitrogen. A gold disk was used as working electrode, platinum wire
was used as counter electrode, and Ag/AgCl (3 M KCl solution) was
used as reference electrode.
2.3.4. N,N-dimethyl-4-(2-(12-phenylindeno[2,1-a]phenalen-7-yl)
ethynyl)benzenamine (4d)
Yield: 75%; m. p. 216e217 ꢀC; 1H NMR (CDCl3, 500 MHz):
d 8.76
(d, J ¼ 7.5 Hz, 1H), 8.38 (d, J ¼ 7.0 Hz, 1H), 7.79 (t, J ¼ 7.5 Hz, 2H), 7.67
(t, J ¼ 8.5 Hz, 3H), 7.60ꢁ7.55 (m, 5H), 7.49 (t, J ¼ 7.0 Hz, 1H),
7.34ꢁ7.23 (m, 3H), 7.11 (d, J ¼ 7.5 Hz, 1H), 6.75 (d, J ¼ 9.0 Hz, 2H),
3.04 (s, 6H); 13C NMR (CDCl3, 125 MHz):
d 150.7, 144.9, 139.7, 137.0,
136.5, 133.5, 133.1, 131.0, 130.2, 129.6, 129.0, 128.7, 128.6, 127.9,
127.8, 127.6, 127.5, 126.4, 126.3, 126.2, 125.3, 124.9, 123.5, 120.3,
120.2, 111.9, 109.6, 104.1, 85.4, 40.2; MS (EI): m/z: 471.2 [Mþ]; Ele-
mental analysis: calcd. for C36H25N: C, 91.69; H, 5.34; N, 2.97, found
C, 91.59; H, 5.29; N, 2.91.
2.3.5. 7-(2-Mesitylethynyl)-12-phenylindeno[2,1-a]phenalene (4e)
Yield: 66%; m. p. 205e206 ꢀC; 1H NMR (CDCl3, 500 MHz):
d 8.81
(d, J ¼ 7.5 Hz, 1H), 8.40 (d, J ¼ 7.5 Hz, 1H), 7.81 (dd, J1 ¼ 7.5 Hz,
J2 ¼ 5.0 Hz, 2H), 7.70 (d, J ¼ 8.0 Hz,1H), 7.61ꢁ7.58 (m, 2H), 7.56ꢁ7.54
(m, 3H), 7.52ꢁ7.48 (m, 1H), 7.29ꢁ7.23 (m, 3H), 7.10 (d, J ¼ 7.0 Hz,
1H), 7.02 (s, 2H), 2.65 (s, 6H), 2.37 (s, 3H); 13C NMR (CDCl3,
2.3. Preparation of indeno[2,1-a]phenalene derivaties 4
General procedure for synthesis of indeno[2,1-a]phenalene
derivaties: A mixture of compound 3 (54.48 mg, 0.12 mmol),
Pd(PPh3)2Cl2 (4.21 mg, 0.006 mmol), CuI (2.30 mg, 0.012 mmol),
PPh3 (3.15 mg, 0.012 mmol) and arylacetylene (0.36 mmol) was
dissolved in 10 mL of Et3N and 10 mL of THF. The reaction mixture
was degassed and stirred at 60 ꢀC for 12 h under a N2 atmosphere.
The solvent was removed under reduced pressure, and the residue
was extracted with CH2Cl2. The organic layer was washed with
water and then brine, dried over anhydrous Na2SO4, and then
evaporated in vacuum to dryness. The residue was purified by silica
gel column chromatography with petroleum ether/chloroform
(30:1, v/v) as an eluent to give the target compounds.
125 MHz):
d 145.0, 140.7, 140.6, 138.9, 137.3, 136.9, 133.4, 133.2,
131.2, 130.4, 129.7, 128.7, 128.6, 128.5, 128.3, 128.1, 128.0, 127.8,
127.6, 126.6, 126.4, 126.3, 125.2, 125.0, 123.5, 120.4, 119.9, 119.8,
100.2, 93.2, 21.6, 21.4; MS (EI): m/z: 470.2 [Mþ]; Elemental analysis:
calcd. for C37H26: C, 94.43; H, 5.57, found C, 94.36; H, 5.48.
2.3.6. 7-(2-(4-Fluorophenyl)ethynyl)-12-phenylindeno[2,1-a]
phenalene (4f)
Yield: 50%; m. p. 192e194 ꢀC; 1H NMR (CDCl3, 300 MHz):
d
8.66ꢁ8.63 (m, 1H), 8.33 (d, J ¼ 7.2 Hz, 1H), 7.84ꢁ7.73 (m, 4H), 7.72
(d, J ¼ 7.8 Hz, 1H), 7.64ꢁ7.52 (m, 6H), 7.34ꢁ7.28 (m, 3H), 7.20 (t,
J ¼ 8.4 Hz, 2H), 7.14ꢁ7.11 (m, 1H); 13C NMR (CDCl3, 125 MHz):
2.3.1. 12-Phenyl-7-(2-phenylethynyl)indeno[2,1-a]phenalene (4a)
Yield: 68%; m. p. 166e167 ꢀC; 1H NMR (CDCl3, 300 MHz):
d
162.11 (d, J ¼ 249.6 Hz), 144.16, 140.39, 136.46, 135.71, 132.87,
132.80, 132.27, 132.17, 129.66, 129.50, 128.72, 127.93, 127.61, 127.40,
127.10, 126.86, 126.33, 125.61, 125.29, 124.48, 124.06, 122.48, 119.47,
118.13, 118.10, 118.02, 115.11 (d, J ¼ 22.1 Hz), 99.46, 85.29; MS (EI):
m/z: 446.2 [Mþ]; HRMS (EI): m/z calcd. for C34H19F: 447.1549
(Mþ þ H); found: 447.1544 (Mþ þ H).
d
8.71ꢁ8.68 (m, 1H), 8.39ꢁ8.35 (m, 1H), 7.82ꢁ7.79 (m, 4H), 7.71 (d,
J ¼ 8.1 Hz, 1H), 7.62ꢁ7.48 (m, 8H), 7.35ꢁ7.25 (m, 4H), 7.12ꢁ7.10 (m,
1H); 13C NMR (CDCl3, 125 MHz):
145.2, 141.3, 137.4, 136.8, 133.3,
d
133.2, 131.9, 130.8, 130.5, 129.7, 129.2, 129.0, 128.7, 128.6, 128.5,
128.4, 128.1, 127.9, 127.4, 126.6, 126.34, 126.31, 125.5, 125.1, 123.6,
123.0, 120.4, 119.2, 101.7, 86.6; MS (EI): m/z: 428.2 [Mþ]; Elemental
analysis: calcd. for C34H20: C, 95.30; H, 4.70, found C, 95.38; H, 4.72.
2.3.7. 7-(2-(4-Chlorophenyl)ethynyl)-12-phenylindeno[2,1-a]
phenalene (4g)
Yield: 60%; m. p. 209e210 ꢀC; 1H NMR (CDCl3, 500 MHz):
2.3.2. 12-Phenyl-7-(2-p-tolylethynyl)indeno[2,1-a]phenalene (4b)
Yield: 70%; m. p. 166e168 ꢀC; 1H NMR (CDCl3, 300 MHz):
d
8.63ꢁ8.62 (m, 1H), 8.30 (d, J ¼ 7.0 Hz, 1H), 7.82 (d, J ¼ 8.0 Hz, 2H),
7.71 (d, J ¼ 8.5 Hz, 3H), 7.62-7.59 (m, 3H), 7.56 (d, J ¼ 7.5 Hz, 2H),
7.51 (t, J ¼ 7.5 Hz, 1H), 7.48ꢁ7.44 (m, 2H), 7.33ꢁ7.28 (m, 3H),
d
8.75ꢁ8.72 (m, 1H), 8.39 (d, J ¼ 7.2 Hz, 1H), 7.85ꢁ7.82 (m, 2H),
7.73ꢁ7.71 (m, 3H), 7.66ꢁ7.52 (m, 6H), 7.38ꢁ7.28 (m, 5H), 7.16ꢁ7.13
(m, 1H), 2.48 (s, 3H); 13C NMR (CDCl3, 125 MHz):
145.1, 141.0,
7.13ꢁ7.11 (m, 1H); 13C NMR (CDCl3, 125 MHz):
d 145.2, 141.6, 137.6,
d
136.7, 135.3, 133.7, 133.3, 133.2, 133.1, 130.6, 130.5, 129.7, 129.1,
128.95, 128.91, 128.6, 128.5, 128.1, 127.9, 127.3, 126.6, 126.3, 125.5,
125.1, 123.5, 121.5, 120.5, 118.9, 100.3, 87.5; MS (EI): m/z: 462.1
[Mþ]; Elemental analysis: calcd. for C34H19Cl: C, 88.21; H, 4.14,
found C, 88.32; H, 4.10.
139.5, 137.2, 136.8, 133.4, 133.2, 131.8, 130.8, 130.4, 129.7, 129.5,
129.0, 128.7, 128.6, 128.3, 128.1, 127.8, 127.5, 126.5, 126.3, 125.5,
125.0, 123.6, 120.4, 120.0, 119.5, 102.1, 86.1, 29.7; MS (EI): m/z: 442.2
[Mþ]; Elemental analysis: calcd. for C35H22: C, 94.99; H, 5.01, found
C, 94.87; H, 5.07.
2.3.8. 7-(2-(3,5-Bis(trifluoromethyl)phenyl)ethynyl)-12-
phenylindeno[2,1-a]phenalene (4h)
2.3.3. 7-(2-(4-Methoxyphenyl)ethynyl)-12-phenylindeno[2,1-a]
phenalene (4c)
Yield: 60%; m. p. 212e214 ꢀC; 1H NMR (CDCl3, 500 MHz):
Yield: 75%; m. p. 206e207 ꢀC; 1H NMR (CDCl3, 500 MHz):
d
8.71
d
8.53ꢁ8.52 (m, 1H), 8.25 (d, J ¼ 7.0 Hz, 1H), 8.17 (s, 2H), 7.96 (s, 1H),
(d, J ¼ 7.0 Hz, 1H), 8.37 (d, J ¼ 7.5 Hz, 1H), 7.82 (dd, J1 ¼ 7.0 Hz,
J2 ¼ 5.0 Hz, 2H), 7.75 (d, J ¼ 8.0 Hz, 2H), 7.71 (d, J ¼ 8.0 Hz, 1H),
7.63ꢁ7.56 (m, 5H), 7.52 (t, J ¼ 7.5 Hz, 1H), 7.36ꢁ7.28 (m, 3H), 7.13 (d,
J ¼ 7.5 Hz, 1H), 7.02 (d, J ¼ 8.5 Hz, 1H), 3.88 (s, 3H); 13C NMR (CDCl3,
7.82 (t, J ¼ 7.0 Hz, 2H), 7.72 (d, J ¼ 8.0 Hz,1H), 7.61 (q, J ¼ 7.5 Hz, 3H),
7.56ꢁ7.51 (m, 3H), 7.34ꢁ7.32 (m, 2H), 7.28 (t, J ¼ 8.0 Hz, 1H),
7.13ꢁ7.11 (m, 1H); 13C NMR (CDCl3, 125 MHz):
d 152.4, 149.4, 145.3,
142.1,138.7,137.9,136.6, 133.2,133.1,130.6,130.4,129.8,129.7,128.9,
128.7, 128.6, 128.4, 128.2, 127.9, 127.3, 126.7, 126.3, 126.2, 125.6,
125 MHz): d 160.5,145.1,140.7,137.1,136.9,133.5,133.2,130.9,130.4,

D. Li et al. / Dyes and Pigments 97 (2013) 389e396
391
125.1, 123.5, 123.4, 120.6, 118.3, 97.7, 89.7; MS (EI): m/z: 564.2 [Mþ];
Elemental analysis: calcd. for C36H18F6: C, 76.59; H, 3.21, found C,
76.51; H, 3.19.
crystals of these compounds can be obtained by slow evaporation
of a solution in a mixture of CHCl3 and CH3OH. Crystal X-ray dif-
fraction intensity data were collected at 100 K on a Bruker-Nonius
Smart Apex CCD diffractometer with graphite-monochromated Mo
KR radiation. The intensity data was processed by using the SAINT
and SADABS routines, and the structure solution and refinement
were carried out by the SHELXTL suite of X-ray programs (version
6.10).
2.3.9. 2-(2-(12-Phenylindeno[2,1-a]phenalen-7-yl)ethynyl)pyridine
(4i)
Yield: 70%; m. p. 188e189 ꢀC; 1H NMR (CDCl3, 500 MHz):
d 8.74
(d, J ¼ 7.5 Hz, 1H), 8.42 (d, J ¼ 7.0 Hz, 1H), 7.82ꢁ7.79 (m, 4H), 7.72 (d,
J ¼ 8.0 Hz, 1H), 7.62ꢁ7.55 (m, 5H), 7.51 (t, J ¼ 7.0 Hz, 1H), 7.38ꢁ7.28
(m, 5H), 7.11 (t, J ¼ 7.0 Hz, 1H); 13C NMR (CDCl3, 125 MHz):
d 150.5,
3.2. Optical properties of compounds 4aej
145.2, 143.2, 142.6, 137.9, 136.6, 136.4, 133.13, 133.10, 130.5, 130.4,
129.7, 128.9, 128.6, 128.4, 128.1, 127.9, 127.8, 126.6, 126.4, 126.2,
125.7, 125.0, 123.9, 123.4, 120.4, 118.2, 100.2, 85.9; MS (EI): m/z:
429.2 [Mþ]; HRMS (EI): m/z calcd. for C33H19N: 430.1596 (Mþ þ H);
found: 430.1590 (Mþ þ H).
The resulting compounds 4aej can show good solubility in
common organic solvents such as CHCl3, CH2Cl2 and THF, etc. Their
UVevis absorption and fluorescence spectra were recorded in
CHCl3 as shown in Fig. 2 and Fig. 3, and the data are collected in
Table 1. Most of these compounds have well-resolved absorption
peaks and large molar absorption coefficients in the range of 300e
2.3.10. 3-(2-(12-Phenylindeno[2,1-a]phenalen-7-yl)ethynyl)
550 nm due to the effective
p p-conjugated
p* transition of the
ꢁ
pyridine (4j)
Yield: 69%; m. p. 188e190 ꢀC; 1H NMR (CDCl3, 500 MHz):
d 9.03
structures. In view of maximum absorption wavelengths of 4aej,
most of these compounds has strong absorption at long wave-
length (about 530 nm) compared to compound 3 (about 515 nm
[6]) due to its coplanarity of indeno[2,1-a]phenalene cycle and aryl
group via triple bond, which can also be observed from crystal
structures of 4aec and 4i. In contrast with quantum yield of com-
pound 3 (VPL ¼ 0.003) containing iodine atom which quenches
fluorescence, compounds 4aej all show higher fluorescence
(s, 1H), 8.68 (d, J ¼ 4.5 Hz, 1H), 8.61ꢁ8.60 (m, 1H), 8.30 (d, J ¼ 7.0 Hz,
1H), 8.05 (d, J ¼ 7.5 Hz, 1H), 7.81 (d, J ¼ 8.0 Hz, 2H), 7.71 (d,
J ¼ 8.0 Hz, 1H), 7.82ꢁ7.59 (m, 3H), 7.57ꢁ7.50 (m, 3H), 7.43 (dd,
J1 ¼7.0 Hz, J2 ¼ 4.5 Hz, 1H), 7.32 (t, J ¼ 4.5 Hz, 2H), 7.28 (t, J ¼ 8.0 Hz,
1H), 7.12 (t, J ¼ 4.5 Hz, 1H); 13C NMR (CDCl3, 125 MHz):
d 152.4,
149.3, 145.2, 142.0, 138.6, 137.8, 136.6, 133.2, 133.1, 130.6, 130.4,
129.8, 129.2, 128.9, 128.6, 128.4, 128.2, 127.9, 127.2, 126.7, 126.3,
126.2, 125.6, 125.1, 123.5, 123.3, 120.6, 120.2, 118.3, 97.6, 89.6; MS
(EI): m/z: 429.2 [Mþ]; HRMS (EI): m/z calcd. for C33H19N: 430.1596
(Mþ þ H); found: 430.1590 (Mþ þ H).
quantum yields (VPL ¼ 0.06e0.16) owing to donor-
-A) structure. Herein, 4f has the highest quantum efficiency of
fluorescence (VPL ¼ 0.16), which can be attributed to the strongest
electron-withdrawing ability of fluorine atom in the D- -A struc-
p-acceptor (D-
p
p
ture (Table 1). As is evident from Fig. 3, it can be found that the
fluorescence spectra of these compounds show obvious difference
by changing the substituted electron donor or electron acceptor
groups. The maximum fluorescence emission wavelengths (lmemax) of
compounds 4bee including electron-donating groups have more
than 60 nm red-shift relative to 4a containing only phenyl group.
And among these compounds, the strongest donor substituted 4d
appears emission peak situated at 490 nm, and has as high as 88 nm
red-shift. Compounds 4fej with electron-withdrawing groups also
3. Results and discussion
3.1. Synthesis of indeno[2,1-a]phenalene-based derivatives
Scheme 1 illustrated the synthetic routes to ten target indeno
[2,1-a]phenalene derivatives 4. 1,8-Bis(2-phenylethynyl)naph-
thalene 2 was prepared in about 86% yield by the Pd-catalyzed
SonogashiraeHagihara coupling of 1,8-diiodonaphthalene 1 and
phenylacetylene at room temperature according to previous liter-
ature [6]. Treatment of compound 2 with I2 afforded 7-iodo-12-
phenylindeno 3 in CHCl3 at 40e50 ꢀC through a domino intra-
molecular electrophilic cyclization mechanism of peri-ethynylene
naphthalene [6]. And then indeno[2,1-a]phenalene derivatives 4a-j
were synthesized by Pd-catalyzed SonogashiraeHagihara reaction
from compound 3 with various arylacetylene in 50e75% yields.
show different red shift due to the formation of D-p-A structure
except 4g. Herein, the indeno[2,1-a]phenalene unit acts as an
electron acceptor in 4a-e, but as a donor in 4f-j.
3.3. Fluorescence change of compound 4d toward solve polarity
These target compounds were fully characterized by 1H NMR, 13
NMR, EI mass spectra and elemental analysis, etc. The structures of
some compounds, such as 4a, 4b, 4c, and 4i were also elucidated by
single-crystal X-ray diffraction analysis (Fig. 1) [9]. X-ray quality
C
Among these compounds, it was found that compound 4d
containing dimethyl amino group appears greatly different ab-
sorption and emission spectra from other derivatives. Herein, we
further investigated its solvatochromic change. The UVevis and
Scheme 1. Synthesis procedures of indeno[2,1-a]phenalene-based derivatives 4aej.

392
D. Li et al. / Dyes and Pigments 97 (2013) 389e396
Fig. 1. Single-crystal structures of compounds 4a (a), 4b (b), 4c (c) and 4i (d).
fluorescence spectra of 4d in various solvents are shown in Fig. 4
and Fig. 5, respectively. The result indicates that compound 4d
presents similar absorption spectra in different polar solvents,
whereas, exhibits obvious red-shift changes of fluorescence spectra
from 490 nm to 607 nm as increasing solvent polarity from CHCl3 to
DMSO (Table 2). Interestingly, visible fluorescence of 4d in various
solvents appears visual color change from blue to red, which can be
clearly observed under a 365 UV lamp (Fig. 5). The results indicate
4d shows solvent polarity dependence. The solvatochromism might
be caused by photoinduced intramolecular charge transfer (ICT) in
the excited state. Such chromic behavior is associated with the
stabilization of the polar emissive excited states by the polar sol-
vents, which also indicates dipoleedipole interactions between
solvent and solute should be considered [10]. In order to under-
stand the solvent effect on the fluorescence emission process, the
solvatochromic Stokes shifts can supply quantitative information
on the dipole moments of the fluorophores based on Lipperte
Mataga equation: Dn
¼
nabs
ꢁ
nem ¼ 2(me
ꢁ
mg
)
2Df/hca3 þ C, which
describes the interactions between the solvent and the diploe
moment of fluorophore [11]. Herein, Dn is Stokes shifts of fluo-
rescence spectra, me and mg are the excited- and ground-state dipole
moments, respectively, h is the Planck’s constant, c is the velocity of
light, a is the radius of the cavity in which the fluorophore resides
(Onsager radius). In addition,
Df as the solvent polarity parameter
can be expressed as (εꢁ1)/(2ε þ 1)-(n2ꢁ1)/(2n2 þ 1), ε and n are the
dielectric constant and refractive index of solvent, respectively.
Df
values for the various solvents could be calculated from known
values of ε and n. The Stokes shift values for 4d were plotted against
Df in Fig. 6 by using CHCl3, diethyl ether, THF, DMSO, DMF, and
Fig. 2. UVevis absorption spectra of compounds 4aej (1 ꢂ 10ꢁ5 mol/L in CHCl3).
Fig. 3. Fluorescence spectra of compounds 4aej in CHCl3.

D. Li et al. / Dyes and Pigments 97 (2013) 389e396
393
Table 1
Photophysical and electrochemical data of compounds 4aej.
b
d
Compounds
UVevis (nm)
lem (nm)
CV
HOMO (eV)a
LUMO (eV)
Egc (eV)
VPL
E1ox
E1red
3e
4a
4b
4c
4d
4e
4f
4g
4h
4i
349, 417, 441, 515
360, 377, 418, 443
381, 402
384, 405, 436, 464
444, 472
409, 436, 490
390 (w), 441, 467
380, 400, 435, 463
383, 405
0.67
0.77
0.66
0.73
e
ꢁ1.55
ꢁ1.49
ꢁ1.57
ꢁ1.54
ꢁ1.55
ꢁ1.56
ꢁ1.20
ꢁ1.52
ꢁ1.45
ꢁ1.50
ꢁ1.49
ꢁ5.38
ꢁ5.42
ꢁ5.37
ꢁ5.39
ꢁ5.32
ꢁ5.40
ꢁ5.44
ꢁ5.41
ꢁ5.52
ꢁ5.42
ꢁ5.39
ꢁ3.33
ꢁ3.40
ꢁ3.30
ꢁ3.35
ꢁ3.32
ꢁ3.32
ꢁ3.66
ꢁ3.37
ꢁ3.43
ꢁ3.38
ꢁ3.39
2.05
2.02
2.07
2.04
2.00
2.08
1.78
2.04
2.09
2.04
2.00
0.003
0.11
0.08
0.07
0.06
0.07
0.16
0.09
0.12
0.11
0.12
243, 259, 431 (w), 530 (w)
243, 257, 432 (w), 530 (w)
240, 260, 434 (w), 534 (w)
272, 300, 358, 483
247, 260, 430 (w), 529 (w)
243, 259, 429 (w), 532 (w)
241, 259
247, 260
243, 259, 428 (w), 532 (w)
244, 260, 428 (w), 533 (w)
0.70
0.78
0.73
0.80
e
416, 441
400, 433, 461
434, 461
4j
e
a
HOMO energy level was calculated from the onset of oxidation wave.
b
c
LUMO energy level was calculated from the onset of the first reduction wave.
The energy levels were calculated by using the following equations: HOMO ¼ -(4.8 þ Eooxnset), LUMO ¼ -(4.8 þ E
), Eg ¼ LUMO-HOMO.
onset
red
d
e
Quantum yields were determined with 9,10-diphenylanthracene as the fluorescence reference in chloroform (V ¼ 0.91).
These data of compound 3 can be found in Ref. [6].
Table 2
UVevis and fluorescence data of 4d in different solvents.
CHCl3
Diethyl
ether
THF
DMSO
DMF
Acetone
labs/nm
lem/nm
485
409, 436,
490
474
404,
490
486
507
437,
607
500
434,
601
484
429,
570
404,
429,
516
1196
0.210
nabsꢁnem/cmꢁ1
210
0.155
689
0.168
3249
0.263
3361
0.276
3117
0.284
D
f
responsible for the large solvent-dependent shifts [12]. The positive
slope of the plot indicates the excited-state dipole moments of this
compound are much larger than ground-state dipole moments. The
obvious solvatochromic red-shift of 4d can be attributed to charge-
transfer (CT) effect on the fluorescent emission, which leads to the
decrease of the energy level and solvent stabilization of excited
state. This effect becomes larger as the solvent polarity increases,
resulting in the emission at a longer wavelength [13]. As a result,
emissions of 4d depend on the solvent polarity and the fluo-
rescence color changes could be directly detected by naked eyes
under UV-lamp, which implies this kind of compound might be
used for solvent polarity sensor.
Fig. 4. UVevis spectra of 4d in various solvents.
acetone. It can be found that the plot of Dn against Df in these dif-
ferent polar solvents has a positive correlation and is nearly linear
with correlation coefficient R ¼ 0.98. Linearity of the plot suggests
that dipoleedipole interactions between the solute and solvent are
Fig. 5. Fluorescence spectra of 4d in various solvents. Inset: visible fluorescence of 4d
in various solvents under a 365 nm UV lamp; solvents from left to right: (1) CHCl3, (2)
diethyl ether, (3) THF, (4) DMSO, (5) DMF, (6) acetone.
Fig. 6. Polt of Stokes shift (Dn) of 4d vs solvent polarity parameter (Df) of various
solvents.

394
D. Li et al. / Dyes and Pigments 97 (2013) 389e396
Fig. 7. Fluorescence spectra of 4d (1.0 ꢂ 10ꢁ5 mol Lꢁ1) in THF with increasing amounts
of Hþ in H2O (0, 2.0, 4.0, 8.0, 12.0, 16.0, 20.0, 28.0, 40.0, 60.0, 80.0, 100.0,
113.0 ꢂ 10ꢁ3 mol$Lꢁ1) (lex ¼ 391 nm, slit width (EX/EM): 5 nm/5 nm).
Fig. 9. SterneVolmer plots of 4d in THF emission quenched by Hþ in H2O.
SterneVolmer plot could be obtained with the KSV value of
9.2 molꢁ1$L (Fig. 9) indicating that indeno[2,1-a]phenalene-based
fluorophore 4d can be used for pH-sensing.
3.4. The fluorescence response of 4d on Hþ
Herein, we further investigated the effects of the fluorescence
response behaviors of 4d on Hþ were in THF/H2O since dimethyl
amino group in 4d is strong electron donor group and has a strong
ability to accept a proton. Fig. 7 shows the fluorescence spectra of
4d (1.0 ꢂ 10ꢁ5 mol$Lꢁ1 in THF) upon the addition of aqueous HCl. As
is evident from Fig. 7, gradual fluorescence quenching could be
observed with increase of Hþ mole ratio. Hþ leads to about 47.9%
fluorescence quenching for 4d at a concentration of 0.1 mol Lꢁ1, and
at the same time, the maximum fluorescence emission wavelength
of the solution shows more than 30 nm red-shift. As shown in Fig. 8,
a curve equation is got in the range of Hþ concentration from 0 to
0.06 mol Lꢁ1 is F ¼ 3.68 ꢂ 105ꢁ2.35 ꢂ 106[Hþ], R ¼ 0.996, N ¼ 10.
According to the equation and the standard deviation of the blank,
the fluorescence detection limit of this compound solution for Hþ
detection can reach as low as 3.30 ꢂ 10ꢁ3 mol Lꢁ1. The quenching
efficiency is related to the SterneVolmer constant, KSV, and deter-
mined by monitoring measurable changes in the fluorescence
spectra via the SterneVolmer equation: F0/F ¼ 1 þ KSV[Q]. Herein, F0
is the fluorescence emission intensity in the absence of the
quencher, and F is the fluorescence emission intensity in the
presence of the quencher. [Q] is the quencher concentration, that is
Hþ concentration. At these concentration ranges of [Hþ], a linear
3.5. Electrochemistry of 4aej
Cyclic voltammetry (CV) analyses of compounds 4aej were
performed to examine their electrochemical behavior and measure
their energy levels (Fig. 10 and Fig. 11, Table 1). Three-electrode
electrochemical cell was used with a gold disc electrode as work-
ing electrode, a platinum wire as counter electrode and an AgCl/Ag
(in 3 M aq. KCl) as reference electrode. The electrochemical mea-
surements were carried out in anhydrous DCM with 0.1 M tetra-
butylammonium hexafluorophosphate (Bu4NPF6) as the
supporting electrolyte at a scan rate of 0.05 V/s at room tempera-
ture under the protection of nitrogen, and redox potentials were
calibrated using a ferrocene-ferrocenium (FceFcþ) redox couple as
an external standard. As is evident from Fig. 3, and Table 1, CV
curves of indeno[2,1-a]phenalene-based derivatives appear qua-
sireversible or irreversible reduction waves similar to the reported
literature [6], and such an amphoteric redox behavior is common
among five-membered-ring-containing PAHs. The HOMO (highest
occupied molecular orbital) and LUMO (lowest unoccupied mo-
lecular orbital) energy levels of these compounds can be estimated
according to the equations of HOMO
¼
ꢁ(4.8
þ
Eoonxset),
Fig. 8. Fluorescence intensity of 4d vs the increasing concentration of Hþ from 0 to
113.0 ꢂ 10ꢁ3 mol Lꢁ1 in THF/H2O. Inset: calibration curve was obtained from the plot of
fluorescence intensity with the added Hþ from 0 to 60.0 ꢂ 10ꢁ3 mol$Lꢁ1
.
Fig. 10. Cyclic voltammograms of compounds 4aee.

D. Li et al. / Dyes and Pigments 97 (2013) 389e396
395
Science Foundation (No. Y4110141) and Commonweal Project of
Science and Technology Department of Zhejiang Province (No.
2012C23030 and 2011R09002-03).
Appendix A. Supplementary data
Supplementary data related to this article can be found at http://
dx.doi.org/10.1016/j.dyepig.2013.01.012.
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Acknowledgments
[9] (a) Compound 4a: C34H20, Mw ¼ 428.50, monoclinic, 0.28 ꢂ 0.15 ꢂ 0.11 mm,
This work was supported by the National Natural Science
Foundation of China (No. 21204066), Zhejiang Provincial Natural
P21/c, a ¼ 12.559(4), b ¼ 22.070(7), c ¼ 8.161(3) Å,
a
¼ 90ꢀ,
b
¼ 93.656(6)ꢀ,
g
¼ 90ꢀ, V ¼ 2257.3(13) Å3, Z ¼ 4, rcalcd ¼ 1.261 Mg/m3, collected 13556,

396
D. Li et al. / Dyes and Pigments 97 (2013) 389e396
independent 4047, parameters 307, R1 ¼ 0.0543, wR2 ¼ 0.1479 (I > 2
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a triphenylamine-
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¼ 71.816(5)ꢀ,
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(I)), GOF ¼ 1.057. CCDC No.: 894162. (c)
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