Synthesis and photophysical characterizations of thermal -stable naphthalene benzimidazoles

Article abstract of DOI:10.1007/s10895-011-0845-z

Microwave-assisted synthesis, photophysical and electrochemical properties of thermal-stable naphthalene benzimidazoles and naphthalimides are studied in this paper. Microwave-assisted synthesis of naphthalene benzimidazoles provide higher yields than the conventional thermal synthesis. Comparative photophysical properties of naphthalene benzimidazoles and naphthalimides are revealed that conjugation of electron-donating group onto naphthalimide moiety increases fluorescence quantum yields. Fluorophore-solvent interactions are also investigated using Lippert-Mataga equation for naphthalimides and naphthalene benzimidazoles. Thermal stabilities of naphthalene benzimidazoles are better than naphthalimides due to increased aromaticity. The experimental ELUMO levels of naphthalene benzimidazoles are found to be between 3.15 and 3.28 eV. Therefore, naphthalene benzimidazole derivatives consisting of anchoring groups are promising materials in organic dye sensitized solar cells. Springer Science+Business Media, LLC 2009.

Full text of DOI:10.1007/s10895-011-0845-z

J Fluoresc (2011) 21:1565–1573
DOI 10.1007/s10895-011-0845-z
ORIGINAL PAPER
Synthesis and Photophysical Characterizations
of Thermal -Stable Naphthalene Benzimidazoles
Sule Erten-Ela & Serdar Ozcelik & Esin Eren
Received: 24 November 2010 /Accepted: 10 January 2011 /Published online: 29 January 2011
#
Springer Science+Business Media, LLC 2011
Abstract Microwave-assisted synthesis, photophysical
and electrochemical properties of thermal-stable naphtha-
lene benzimidazoles and naphthalimides are studied in
this paper. Microwave-assisted synthesis of naphthalene
benzimidazoles provide higher yields than the conven-
tional thermal synthesis. Comparative photophysical
properties of naphthalene benzimidazoles and naphthali-
mides are revealed that conjugation of electron-donating
group onto naphthalimide moiety increases fluorescence
quantum yields. Fluorophore-solvent interactions are also
investigated using Lippert-Mataga equation for naphtha-
limides and naphthalene benzimidazoles. Thermal stabil-
ities of naphthalene benzimidazoles are better than
naphthalimides due to increased aromaticity. The exper-
imental ELUMO levels of naphthalene benzimidazoles are
found to be between 3.15 and 3.28 eV. Therefore,
naphthalene benzimidazole derivatives consisting of an-
choring groups are promising materials in organic dye
sensitized solar cells.
Introduction
Naphthalimides are well-known as promising anticancer
agents showing broad-spectrum activity against a variety of
human solid tumor cells [1, 2]. Several derivatives have
reached the phases of clinical trials [3]. N-Substituted 1,8-
naphthalimides find a wide range of applications as organic
dyes and luminophores.
1,8-Naphthalimides are generally fluorescent compounds
for which a series of biological (local anesthetics [4], DNA
cleaving agents [5], tumoricidals [6] and non-biological
optical brighteners [7], lucifer dyes [8]) applications have
been found. 1,8-Naphthalimide and bisnaphthalimide deriv-
atives are promising anticancer agents [9, 10], the sulfonat-
ed derivatives are good antiviral agents with selective in
vitro activity against the human immunity deficiency virus,
HIV-1 [11]. Due to their photo-physical and photo-chemical
properties the 1,8-naphthalimide derivatives can be used as
fluorescence dyes for solar energy collectors and photosyn-
thesis under concentrated sunlight [12], fluorescent markers
in biological cells [13] as well as laser active media [14–
16]. Recently, naphthalimides have also found applications
in organic thin film field-effect transistors (OFETs),
integrated circuit, displays, memory cards, chemical and
pressure sensors, smart price tags and labels [17].
.
.
Keywords Naphthalene benzimidazole Naphthalimide
.
.
.
Absorption Emission Cyclic voltammetry TGA curves
The electronic absorption and emission spectra of
naphthalimides are effected by substitutions. In general,
naphthalimides present lower fluorescence quantum yields.
Photophysical behaviors of naphthalene benzimidazoles are
different from naphthalimides. Conjugation of electron-
donating groups onto naphthalimide moiety increases
fluorescence emission. This study presents the microwave
assisted synthesis of thermal-stable naphthalene benzimi-
dazoles. Fluorescence quantum yields of NB_I and NB_II
are found to be 0.36 and 0.60, respectively. This is very
:
S. Erten-Ela (*) E. Eren
Ege University, Solar Energy Institute,
35100 Bornova, Izmir, Turkey
e-mail: suleerten@yahoo.com
S. Erten-Ela
e-mail: sule.erten@ege.edu.tr
S. Ozcelik
Chemistry Department, Izmir Institute of Technology,
Urla, 35430 Izmir, Turkey

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J Fluoresc (2011) 21:1565–1573
Table 1 Synthesized naphthalimide and naphthalene benzimidazole derivatives
CH
CH
3
3
O
N
O
O
N
O
CH
3
NI_I
NI_II
N-Butyl-1,8-naphthalimide
N-2-Ethyl hexyl-1,8-naphthalimide
N
N
N
N
N
NB_I
NB_II
O
O
1,8-Naphthalene benzimidazole
1,8-Naphthalene(3,4-pyridine imidazole)
similar to what we calculated in the case of naphthalene
benzimidazole (NB_I) derivative [18–20]. The photophys-
ical and electrochemical properties of naphthalene benzi-
midazoles (NBs) were compared to naphthalimides (NIs).
Conventional thermal synthesis of naphthalimides requires
8–10 h. Instead of this conventional process, we have used
microwave method to synthesize naphthalimides and
naphthalene benzimidazoles. We obtained 85–90% yields
with microwave heating in 20 min. When compared with
conventional thermal heating method, microwave heating
method has some advantages such as high reaction yield,
faster reaction time, rapid heating of the medium, enhanced
reaction selectivity and saving energy due to completed
reactions in short time.
And also, general and specific solvent effects of
naphthalene benzimidazoles (NBs) and naphthalimides
(NIs) were investigated using Lippert-Mataga equation.
Molecular structures of naphthalimide (NI) and naphtha-
lene benzimidazole (NB) derivatives are presented in
Table 1.
Fig. 1 Cyclic voltammogram of
NI_II (a), and NB_I (b), in
acetonitrile

J Fluoresc (2011) 21:1565–1573
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Table 2 ELUMO and EHOMO
energy levels of synthesized NI
and NB derivatives
E0−E−1, Volt
ELUMO, eV
EHOMO, eV
Band Gap, eV
NI_I
−1.34
−1.39
−1.26
−1.14
3.07
3.02
3.15
3.28
5.51
5.59
5.62
5.57
2.44
2.57
2.47
2.29
NI_II
NB_I
NB_II
Eferrocene = 0.39 V (Ferrocene is
internal reference electrode)
E0−E−1 = Reduction potentials
of synthesized derivatives
Experimental
microwave oven. The reaction has been completed in
20 min which was found to be an optimum time. After
20 min, solution was cooled and treated with 2 N of HCl to
remove excess imidazole. Then, the material was filtered
and washed with water. The crude product was purified by
silicagel column chromatography, using CH2Cl2 as eluent.
The reaction yield is 90% for naphthalimide (white color);
85% for naphthalene benzimidazole (yellow color) for
microwave heating method. Solubility of N-butyl-1,8-
naphthalimide is 300 mg/ml in CH2Cl2, N-2-ethyl hexyl-
1,8-naphthalimide is 450 mg/ml in CH2Cl2; solubility of
1,8-naphthalene benzimidazole is 60 mg/ml in CH2Cl2.
solubility of 1,8-Naphthalene(3,4-pyridine imidazole) is
40 mg/ml in CH2Cl2. Materials were characterized using
1H-NMR, IR and Elemantal Analysis.
Materials
1,8-Naphthalic anhydride, 2-ethyl hexyl amine, butyl amine,
o-phenylene diamine, 3,4-diamino pyridine, anthracene were
purchased from Aldrich. Quinine sulfate was supplied from
Acros Organics. The fluorescence quantum yields of
naphthalene benzimidazoles were measured using quinine
sulfate as the reference compound (’f=0.546 in 1N H2SO4).
All solvents were of spectroscopic grade and were used
without any further purification.
Materials Characterization
The UV–vis absorption spectra were recorded in an
Analytic JENA S 600. Fluorescence spectra were obtained
in a PTI QM1 fluorescence spectrophotometer. Concen-
trations were arranged to 10−6 M in order to avoid
aggregation or reabsorption effects for absorption, fluores-
cence and quantum yield measurements. Quinine sulfate
was used as the fluorescence quantum yield standard for
naphthalene benzimidazole and 1,8-naphthalene(3,4-pyri-
dine imidazole). Anthracene was used as the fluorescence
quantum yield standard for naphthalene imides. Cyclic
voltammetry measurements of synthesized naphthalimide
and naphthalene benzimidazole derivatives were taken
using CH-Instrument 660 B Model Potentiostat equipment.
Thermal stabilities were determined by means of thermal
gravimetry measurements (TGA) with the equipment of
Perkin Elmer- Thermogravimetric Analyzer Pyris 6 TGA.
-N-Butyl-1,8-naphthalene imide; NI_I, IR (KBr): cm−1,
3050, 2950, 1700, 1650, 1575, 1455, 1380, 1250, 1190,
1085, 990, 880, 750.
1H NMR (CDCl3), (ppm), 8.6(2H, s), 8.2(2H, s), 7.7(2H,
s), 4.3(2H, m), 1.7(2H, m), 1.45(2H, m), 1.0 (3H, m).
C16H15NO2 (253): Calcd: C 75.87%, H 5.97%, N
5.53%, O 12.63%; found: C 75.88%, H 5.99%, N 5.52%,
O 12.64%.
-N-2-Ethyl hexyl-1,8-naphthalene imide, NI_II, IR
(KBr): cm−1, 3063, 2957, 2924, 2872, 2856, 1700, 1654,
1625, 1590, 1534, 1498, 1512, 1459, 1438, 1416, 1388,
1346, 1318, 1278, 1236, 1205, 1185, 1168, 1133, 1083,
1073, 1026, 949, 916, 900, 857, 847, 799, 783, 738.
1H NMR (CDCl3): (ppm), 8.6 (2H, s), 8.2 (2H, s), 7.6
(2H, s), 4.1 (2H, m), 1.9 (H, m), 1.3 (8H, m), 0.9 (6H, m).
C20H23NO2 (309): Calcd: C 77.64%, H 7.49%, N
4.53%, O 10.34%; found: C 77.65%, H 7.51%, N 4.53%,
O 10.34%.
Synthesis and Characterization of Naphthalimide (NI)
and Naphthalene Benzimidazole (NB) Derivatives
-1,8-Naphthalene benzimidazole, NB_I, IR (KBr):
cm−1, 3060, 1696, 1671, 1640, 1618, 1583, 1551, 1501,
1449, 1362, 1322, 1289, 1230, 1177, 1150, 1122, 1072,
1029, 917, 880, 840, 750, 700, 670, 617.
A microwave oven, CEM MARS-5, frequency 2.45 GHz,
maximum power 700 W, was used to synthesize naphtha-
limide and naphthalene benzimidazole derivatives. Naph-
thalimides and naphthalene benzimidazoles have been
synthesized by condensation reaction of 1,8-naphthalic
anhydride and primary amine or o-phenylene diamine in
imidazole solutions, using microwave oven. 1,8-Naphthalic
anhydride (1 g, 0.005 mol), a primary amine (0.36 g,
0.005 mol) or o-phenylene diamine (0.55 g, 0.005 mol) and
imidazole (10 g) were placed in to XP-1500-plus vessel of
1H NMR (CDCl3): (ppm), 8.80 (2H, d), 8.56 (H, m), 8.26
(H, d), 8.12 (H, d), 7.88 (H, m), 7.78 (2H, m), 7.48 (2H, m).
C18H10N2O (270): Calcd: C 79.99%, H 3.73%, N
10.36%, O 5.92%; found: C 79.96%, H 3.75%, N
10.36%, O 5.93%.
-1,8-Naphthalene(3,4-pyridine imidazole), NB_II, IR
(KBr): cm−1, 3057, 1700, 1640, 1619, 1540, 1500, 1440,
1362, 1327, 1261, 1236, 1181, 1140, 1031, 819, 770, 601.

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J Fluoresc (2011) 21:1565–1573
a)
b)
Fig. 2 TGA curve of NI_II (a), and NB_I (b)

J Fluoresc (2011) 21:1565–1573
1569
Table 3 UV/Vis spectroscopy data and Fluorescence emission maxima of NI_I and NI_II in dichloromethane, DMF, Acetonitrile, THF, Hexane,
Methanol
lmf ax (nm)
ε
Refraction l1 (nm) ε1 (M−1cm−1
index
)
l2 (nm) ε2 (M−1cm−1
)
l3 (nm) ε3 (M−1cm−1
)
Stokes
shift
(cm−1
)
NI_I Acetonitrile
37.5
36.7
1.3441
1.4303
1.4242
1.4076
1.372
318
318
319
318
312
316
317
320
320
318
312
316
11767
13460
17050
10632
9202
332
334
334
332
326
333
332
334
334
332
328
333
16098
18755
24000
14178
12474
10651
12640
14810
15450
13730
10695
9656
348
349
344
345
342
343
347
349
349
347
343
343
14359
16456
21875
12552
12308
10167
11940
13520
13340
12015
10378
9046
380
384
383
377
364
384
382
384
381
378
368
387
1190
1410
1600
1210
590
DMF
Dichloromethane 8.93
THF
Hexane
7.6
1.87
Methanol
33.1
1.326
7182
2417
1570
1630
1330
1190
910
NI_II Acetonitrile
DMF
37.5
36.7
1.3441
1.4303
1.4242
1.4076
1.372
9130
10945
11235
9440
Dichloromethane 8.93
THF
7.6
Hexane
Methanol
1.87
8101
33.1
1.326
6718
2200
lmf ax, nm, fluorescence emission maxima
ε1, M−1 cm−1 , molar extinction coefficient
1H NMR (CDCl3): (ppm), 9.24 (H, s), 8.90 (H, d), 8.82
(H, d), 8.68 (H, d), 8.50 (H, d), 8.35 (H, d), 8.24 (H, d), 7.86
(2H, m).
C17H9N3O (271): Calcd: C 75.27%, H 3.34%, N
15.49%, O 5.90%; found: C 75.26%, H 3.34%, N
15.50%, O 5.92%.
100–500 mV/s under nitrogen at 25 °C. Solutions of NI and
NB derivatives were prepared in chloroform (10−3 M). A
three electrode cell was used consisting of glassy carbon
working electrode, Pt wire counter electrode and Ag/AgCl
reference electrode, all placed in a glass vessel. Tetrabuty-
lamonium hexafluorophosphate (TBAPF6), 0.1 M, was
used as supporting electrolyte. Ferrocene was used as
internal reference electrode. NI and NB derivatives show
both quasi-reversible reduction and oxidation potential in
Fig. 1. In calculation, the zero vacuum level of ferrocene
was taken as 4.8 eV [21, 22]. We used the following
equation to calculate EHOMO and ELUMO energy level of
Electrochemistry of Naphthalimide (NI) and Naphthalene
Benzimidazole (NB) Derivatives
EHOMO and ELUMO values of NIs and NBs were calculated
using cyclic voltammograms with scan rates in the range of
Table 4 UV/Vis spectroscopy data and fluorescence emission maxima of NB_I and NB_II in dichloromethane, DMF, Acetonitrile, THF, Hexane,
Methanol
lmf ax (nm)
ε
Refraction index l1 (nm) ε1 (M−1cm−1
)
l2 (nm) ε2 (M−1cm−1
)
Stokes shift (cm−1
)
NB_I
Acetonitrile
DMF
37.5
36.7
1.3441
1.4303
1.4242
1.4076
1.3720
1.3260
1.3441
1.4303
1.4242
1.4076
1.3720
1.3260
331
331
333
333
343
344
347
348
350
347
347
350
6840
6080
379
383
385
382
380
382
374
378
380
375
373
372
12435
9965
492
490
488
485
470
499
469
470
464
464
455
450
6060
5700
5560
5480
4010
6140
5420
5180
4760
5110
3870
4660
Dichloromethane
THF
8.93
10135
7980
15710
13480
10590
13295
12466
17791
18713
13800
9990
7.6
Hexane
1.87
6523
Methanol
33.1
8693
NB_II Acetonitrile
37.5
36.7
8808
DMF
12602
12873
10276
7826
Dichloromethane
8.93
THF
7.6
Hexane
Methanol
1.87
33.1
10263
13151
lmf ax, nm, fluorescence emission maxima
M−1 cm−1 , molar extinction coefficient
ε
1,

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J Fluoresc (2011) 21:1565–1573
Table 5 Fluorescence emission maxima and quantum yield of
naphthalimides and naphthalene benzimidazoles, in acetonitrile
(a); the temperature range for naphthalene benzimidazoles is
between 300 °C and ends at 415 °C, Fig. 2(b). Naphthalene
benzimidazole derivatives have high thermal stabilities,
pointing their favorability in photovoltaic applications.
lmf ax (nm)
Φf (Quantum yield)
NI_I
380
380
492
469
0.018
0.011
0.36
NI_II
NB_I
NB_II
Absorption and Fluorescence Emission of Naphthalimide
(NI) and Naphthalene Benzimidazole (NB) Derivatives
0.60
The UV–vis absorption spectra and fluorescence emission
spectra of NI and NB derivatives have been studied in
various solvents of different polarity and the spectral data
have been collected in Table 1. UV–vis Absorption and
fluorescence emission spectrs of NI and NB derivatives
were taken in acetonitrile, DMF, dichloromethane, THF,
methanol and hexane in Figs. 5 and 6. Quantum yields were
calculated using fluorescence quantum yield standards.
Excitation wavelengths of NIs and NBs are determined as
333 nm and 350 nm, respectively. Fluorescence quantum
yields of the NIs and NBs, measured in acetonitrile, are
collected in Table 5. Among compounds, N-butyl and
N-2-ethylhexyl substituted naphthalimides give three
characteristic band at 320 nm, 334 nm, 349 nm in Table 3.
lmf ax, nm, fluorescence emission maxima
ff, Quantum yield
À
Á
NIs and NBs, ELUMO ¼ ꢀe E1=2ðredoxÞ ꢀ Efer: þ 4:8 [19].
EHOMO and ELUMO energy levels of NI and NB derivatives
are found to be in between 5.51 and 5.62 eV and 3.02 and
3.28 eV, respectively. The CV values are presented in
Table 2. ELUMO energy levels of naphthalene benzimid-
azole derivatives are higher than the conduction band of
TiO2, ECB(TiO2)=4.2 eV. Naphthalene benzimidazole
derivatives absorb in the visible region. They are promising
materials for organic photovoltaics [21, 22].
Results and Discussion
a)
0,5
80000
Thermal Stabilities of Naphthalimide (NI) and Naphthalene
Benzimidazole (NB) Derivatives
0,4
60000
Thermal stabilities of synthesized compounds are determined
using thermal gravimetry measurements. TGA curves of
NI_II and NB_I are presented in Fig. 2. Naphthalene
benzimidazole derivatives are found to be more stable than
naphthalimide derivatives. Decomposition temperature of
naphthalimides starts from 200 °C and ends at 341 °C, Fig. 2
0,3
40000
0,2
20000
0,1
0,0
0
NB_I
NI_I
300
350
400
450
500
0,7
Wavelength (nm)
NB_II
NI_II
0,6
b)
1400000
1200000
1000000
800000
600000
400000
200000
0
0,40
0,35
0,30
0,25
0,20
0,15
0,10
0,05
0,5
0,4
0,3
0,2
0,1
0,0
400
600
800
Wavelength (nm)
350
400
450
500
550
600
Wavelength (nm)
Fig. 3 Absorption spectra of N-butyl-1,8-naphthalimide, NI_I; N-2-
ethylhexyl-1,8-naphthalimide, NI_II; 1,8-naphthalene benzimidazole,
NB_I; 1,8-naphthalene(3,4-pyridine imidazole), NB_II, in acetonitrile
Fig. 4 Absorption and Fluorescence emission spectra of NI_II (a) and
NB_II (b) in acetonitrile (Mirror Image)

J Fluoresc (2011) 21:1565–1573
1571
N-substituted 1,8-naphthalimides have a wavelength of
maximum fluorescence emission ðlmf axÞ of 380 nm in
Table 5. Absorption bands of naphthalene benzimidazole
and 1,8-naphthalene(3,4-pyridine imidazole) range from
300 nm to 430 nm in different solvents, Table 4. As shown
in Table 5, NB_I and NB_II have wavelengths of maximum
emissions of 469 nm and 492 nm. The results show that
electron-donating substituents such as phenylene onto naph-
thalimide moities had very strong influence on the absorption,
fluorescence emission and lead to a red-shifted phenomena.
N-butyl and N-2-ethylhexyl-1,8-napthalimides display
a weak fluorescence quantum yields; Φf=0.018 and
0.011, respectively. In agreement with literature data, E.
Martin et al. and V. Wintgens et al. have reported that the
low value of fluorescence quantum efficiency for naph-
thalimides is associated to an effective intersystem
crossing (ISC) between the singlet excited state S1 and
the nearby triplet state; the ISC efficiency is reported
around 0.95 and 1.0 in acetonitrile and hexane solution,
respectively [21–23]. On the other hand, 1,8-naphthalene
benzimidazole having an electrondonating substituent are
highly fluorescent. The presence of a conjugated electron-
donor group condensed onto the naphthalimide moiety
alters the emission spectra considerably (Figs. 5 and 6).
These substituents cause high red-shifts in fluorescence
spectra (Δλf: 89–112 nm) and substantially increase the
fluorescence yields (Φf) from 0.011, 0.018 to 0.36, 0.60,
(Figs. 3, 4 and Table 5). NB_I shows higher fluorescence
quantum yield of 0.36, with respect to naphthalimides of
NI_I and NI_II, a clear observation of enhanced conjuga-
tion effect by phenylene ring condensation. Highest
quantum yield observed for NB_II (Φf =0.60). The
presence of electron donating substituents may also
increase the separation between the singlet (S1) and its
closer triplet excited state, thus decreasing the intersystem
crossing (ISC) and favoring the fluorescence deactivation
channel [24–32] (Figs. 5 and 6).
The band position of Absorption and emission spectra
for NIs and NBs depend on the change in solvent’s polarity.
a)
0,15
in acetonitrile
in dichloromethane
in DMF
in THF
0,10
0,05
0,00
in hexane
in methanol
a)
0,24
in DMF
0,22
0,20
0,18
0,16
0,14
0,12
0,10
0,08
0,06
0,04
0,02
0,00
in dichloromethane
in acetonitrile
in THF
in hexane
in methanol
350
400
450
500
550
600
Wavelength (nm)
325
350
375
400
425
450
Wavelength (nm)
b)
in acetonitrile
in THF
350000
300000
250000
200000
150000
100000
50000
0
b)
160000
140000
120000
100000
80000
60000
40000
20000
0
in DMF
in acetonitrile
in dichloromethane
in THF
in dichloromethane
in methanol
in hexane
in DMF
in hexane
in methanol
360
450
540
630
420
450
480
510
540
570
600
630
660
Wavelength (nm)
Wavelength (nm)
Fig. 5 Absorption (a) and Fluorescence Emission (b) spectra of N-2-
ethylhexyl-1,8-Naphthalimide, NI_II in different solvents
Fig. 6 Absorption (a) and Fluorescence emission (b) spectra of 1,8-
naphthalene benzimidazole, NB_I in different solvents

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J Fluoresc (2011) 21:1565–1573
Fig. 7 Effects of solvent polar-
ity in the Stokes’ shift of NIs
and NBs in the solvents (a, b, c,
d). The numbers refer to the
following solvents: 1, hexane; 2,
THF; 3, dichloromethane; 4,
DMF; 5, acetonitrile; 6, metha-
nol
[NI_I]
a
c
b
3
2,5
2
[NI_II]
2,5
2
6
6
4
3
2
5
1,5
1
4
1,5
1
3
2
5
1
1
0,5
0,5
0
0
-0,05
0
0,05 0,1 0,15 0,2 0,25 0,3 0,35
-0,05
0
0,05 0,1 0,15 0,2 0,25 0,3 0,35
Δf
Δf
d
[NB_II]
6
5
4
3
2
1
0
5
2
4
[NB_I]
6
7
6
5
4
3
2
1
0
2
6
3
4
5
1
3
1
-0,05
0
0,05 0,1 0,15 0,2 0,25 0,3 0,35
-0,05
0
0,05 0,1 0,15 0,2 0,25 0,3 0,35
Δf
Δf
We also tried to examine the effect of solvent’s polarity on
the molecular structures. The Absorption bands of naph-
thalimides are revealed an influence of the solvent’s
polarity. The solvent effects the characteristics of the
spectra of solute molecules. The responses of NI and NB
derivatives to solvent polarity can be analyzed in terms of
the difference in the dipole moments in the ground and
excited states. This can also be further estimated from a
Lippert-Mataga plot (Fig. 7), which is essentially a plot of
the Stokes shift of the fluorescence emission vs the solvent
polarity. The difference in the maximum absorption and
emission wavelengths, expressed in wavenumbers ð$UÞ, is
fitted to the following equation. The difference between the
maximum absorption and emission wavelengths, expressed
in wavenumbers (νa–vf), is correlated with the solvent
polarity parameter (Δf).
spectral shifts. Specific solvent effects lead to nonlinear
Lippert Plots. General solvent effects are due to the
interactions of the dipole of the fluorophore with its
environment. Specific solvent effects is because of
fluorophore-solvent interactions and specific effects can
be due to hydrogen bonding or charge-transfer interactions.
Stokes’ shifts for NI and NB derivatives have been
calculated in various solvents of different polarity and the
data have been collected in Tables 3 and 4. As a result, it is
found that Lippert curves for NI derivatives are non-linear,
Lippert curves for naphthalene benzimidazoles are linear
(Fig. 7).
Conclusion
In conclusion, thermal-stable naphthalene benzimidazoles
were successfully synthesized. Absorption and emission
spectra were studied in different solvents. Moreover, it was
observed that phenylene groups onto naphthalimide moiety
effect the Absorption and emission wavelengths, quantum
yields, thermal stabilities and electrochemistry of naphtha-
lene benzimidazoles. Naphthalene benzimidazole com-
pounds may serve as good light-emitting materials,
because they emit light in the range of 420 nm–630 nm.
ELUMO values of naphthalene benzimidazoles are found to
be between 3.15 and 3.28 eV. Naphthalene benzimidazole
derivatives can inject electrons to the conduction band of
titanium dioxide in dye sensitized solar cell. Naphthalene
benzimidazole derivatives are also promising materials in
organic solar cells.
2
2ðme ꢀ mgÞ
Ua ꢀ Uf ¼
Δf þ constant
hca3
Where, μe − μg is the difference (Δμ) between the
dipole moments of the excited and the ground states,
respectively, c is the velocity of light,, and R is the radius of
the Onsager cavity around the fluorophore. The parameters
ε and n are the solvent dielectric constant and refraction
index, respectively, which are grouped in the term Δf,
known as orientation polarizability. A plot of ΔU versus Δf
gives Δμ [33–35].
" ꢀ 1
n2 ꢀ 1
Δf ¼
ꢀ
2" þ 1 2n2 þ 1
The linearity of these plots is often regarded as evidence
for the dominant importance of general solvent effects in
Acknowledgements We acknowledge financial support from Scien-
tific and Technological Research Council of Turkey, TUBITAK,

J Fluoresc (2011) 21:1565–1573
1573
TBAG_106T061 and the Alexander von Humboldt Foundation of
Germany and European Science Foundation (ESF) for research
supports. I thank Mechanical Engineer DI. Cagatay Ela for proof-
reading.
15. Pardo A, Martin E, Poyato JML, Camacho JJ, Guerra JM,
Weigand R, Braña JMF, Castellano JM (1989) J Photochem
Photobiol, A 48:259
16. Martin E, Weigand R, Pardo A (1996) J Lumin 68:157
17. Singh ThB, Erten S, Gunes S, Zafer C, Turkmen G, Kuban B,
Teoman Y, Sariciftci NS, Icli S (2006) Org Electron 7:480
18. Plakidin VL, Kosheleva ES (1975) Zhur Organ Khim 11:1512
19. Jiang W, Tang J, Qi Q, Sun Y, Ye H, Fu D (2009) Dyes Pigm 3:279
20. Martin E, Coronado JLGu, Camacho JJ, Pardo A (2005) J
Photochem Photobiol, A 175:1
21. Erten S, Eren E, Icli S (2007) Eur Phys J Appl Phys 38:227
22. Erten S, Icli S (2008) Inorg Chim Acta 361:595
23. Wintgens V, Valat P, Kossanyi J, Demeter A, Biczok L, Berces T
(1996) New J Chem 20:1149
24. Lee CM, Kumler WD (1962) J Org Chem 27:2055
25. Berci FP, Toscano VG, Politi MJ (1988) J Photochem Photobiol,
A 43:51
References
1. Bailly C, Carrasco C, Joubert A, Bal C, Wattez N, Hildebrand MP,
Lansiaux A, Colson P, Houssier C, Cacho M, Ramos A, Brãna
MF (2003) Biochemistry 42:4136
2. Brãna MF, Ramos A (2001) Curr Med Chem Anticancer Agents 1:237
3. Zsombor M, József N, László B, Krisztina SN, Tamás K (2006) J
Photochem Photobiol, A 99:182
4. Settimo AD, Primofiore G, Ferrarini PL, Ferretti M, Barili PL,
Tellini N, Bianchini P (1989) Eur J Med Chem 24:263
5. Saito I (1992) Pure Appl Chem 64:1305
6. Kirshenbaum MR, Chen SF, Behrens CH, Papp LM, Stafford MM,
Sun JH, Behrens DL, Fredericks JR, Polkus ST, Sipple P, Patten AD,
Dexter D, Seitz SP, Gross JL (1994) Cancer Res 54:2199
7. Dorlars A, Schellhammer CW, Schroeder J (1975) Angew Chem
Int Ed Engl 14:665
26. Almeida FCL, Toscano VG, Dos Santos O, Politi MJ,
Neumann MG, Berci Filho P (1991) J Photochem Photobiol,
A 58:289
27. Wintgens V, Valat P, Kossanyi J, Biczok L, Demeter A, Bérces T
(1994) J Chem Soc, Faraday Trans 90:411
28. Brochsztain S, Rodrigues MA, Politi MJ (1997) J Photochem
Photobiol, A Chem 107:195
8. Stewart WW (1981) Nature 292:17
9. Brana MF, Castellano JM, Roldan CM, Santos A, Vazquez D,
Jimenez A (1980) Cancer Chemother Pharmacol 4:61
10. Braña MF, Castellano JM, Morán M, Pérez de Vega MJ, Qian XD,
Romerdahl CA, Keilhauer G (1995) Eur J Med Chem 30:235
11. Chatterjee S, Pramanik S, Hossain SU, Bhattacharya S, Subhash
Bhattacharya C (2007) J Photochem Photobiol, A 187:64
12. Xuhong Q, Zhenghua Z, Kongchang C (1989) Dyes Pigm 11:13
13. Marling JB, Hawley JG, Liston EM, Grant WB (1974) Appl Opt
13:2317
29. Barros TC, Molinari GR, Berci Filho P, Toscano VG, Politi MJ
(1993) J Photochem Photobiol, A Chem 76:55
30. Demets GJ-F, Triboni ER, Alvarez EB, Arantes GM, Filho PB,
Politi MJ (2006) Spectrochim Acta A 63:220–226
31. Niu CG, Qin PZ, Zeng GM, Gui XQ, Guan AL (2007) Anal
Bioanal Chem 387:1067
32. Nandhikonda P, Begaye MP, Cao Z, Heagy MD (2009) Chem
Commun 45:4941–4943
33. Lippert VEZ (1957) Elektrochem 61:962
14. Grabchev I, Moneva I, Bojinov V, Guittonneau S (2000) J Mater
Chem 10:1291
34. Mataga N, Kaifu Y, Koizumi M (1956) Bull Chem Soc Jpn 29:465
35. Mataga N (1963) Bull Chem Soc Jpn 36:654