Spectral properties of chalcone containing triphenylamino structural unit in solution and in polymer matrices

Article abstract of DOI:10.1016/j.dyepig.2011.07.011

Novel chalcones (3-phenyl-1-phenylprop-2-en-1-ones) substituted on one end (position 3) with electron donating diphenylaminophenyl substituent and on the other end (position 1) with thiophenes with variable electronic effects (CH-1-CH-5) were prepared. Th

Full text of DOI:10.1016/j.dyepig.2011.07.011

Dyes and Pigments 92 (2012) 1257e1265
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Dyes and Pigments
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Spectral properties of chalcone containing triphenylamino structural unit
in solution and in polymer matrices
,
b
a
a
b
Martin Danko a , Anita Andics , Csaba Kosa , Pavol Hrdlovic , Daniel Vegh
*
a Polymer Institute, Slovak Academy of Sciences, Dubravska Cesta 9, 845 41 Bratislava, Slovak Republic
b Department of Organic Chemistry, Slovak University of Technology, Radlinskeho 9, SK-812 37 Bratislava, Slovak Republic
a r t i c l e i n f o
a b s t r a c t
Article history:
Novel chalcones (3-phenyl-1-phenylprop-2-en-1-ones) substituted on one end (position 3) with electron
donating diphenylaminophenyl substituent and on the other end (position 1) with thiophenes with
variable electronic effects (CH-1eCH-5) were prepared. The spectral properties of these molecules in
solvents such as chloroform, cyclohexane, acetonitrile, methanol and incorporated into polymer matrices
of polystyrene (PS), poly(methyl methacrylate) (PMMA) and poly(vinyl chloride) (PVC) were compared
with those of 3-[4-(N,N-dimethylamino)-phenyl]-1-phenylprop-2-en-1-one (CH-1m) and 3-[4-(N,N-
dimethylamino)phenyl]-1-(4-nitrophenyl)prop-2-en-1-one (CH-2m). The longest wavelength absorp-
tion band of model chalcones CH-1m and CH-2m was in the range of 400e420 nm and did not appear to
be influenced by the medium. The fluorescence increased with the addition of acetonitrile, while it was
effectively quenched in methanol. The strong electron-attracting nitro group quenched the fluorescence
of CH-2m in nearly all solvents. In contrast, the fluorescence became more intense when the molecule
was incorporated in a polymer matrix. The longest wavelength absorption band of novel chalcones was
observed in the range of 410e450 nm in all media. The fluorescence of chalcones was red-shifted to the
range of 530e575 nm and was most intense in chloroform. The quantum yield of fluorecence was the
highest in chloroform for the chalcone with a methyl-thiophene (0.49) and low for the chalcone with
a fluorenyl-thiophene group (0.07). The fluorescence of all chalcones (CH-1eCH-5) was effectively
quenched in polar acetonitrile and methanol, and was less intense relative to chloroform when incor-
porated into a polymer matrix and more intense relative to other solvents. The lifetime of fluorescence
was in the range of 1e4 ns. The Stokes shift was in the range of 4000e5000 cmꢀ1 in chloroform, and
lower in all other media. The spectral behavior of model chalcones CH-1m and CH-2m and novel
chalcones with diphenylamino substituents was similar, producing observable fluorescence in several
polymer matrices. The effect of the solvent on the fluorescence is discussed in terms of negative and
positive solvatokinetic effects.
Received 4 April 2011
Received in revised form
16 June 2011
Accepted 22 July 2011
Available online 30 July 2011
Keywords:
Fluorescence
Chalcones
Triphenylamine
Thiophene
Solvent effect
Polymer matrice
Ó 2011 Elsevier Ltd. All rights reserved.
1. Introduction
parameters necessary for the further development of the photonic
material itself and the technology based around it.
The emerging science of photonics, which includes the gener-
ation, emission, transmission, modulation, signal processing,
switching, amplification, detection and sensing of light, is being
explored today as the basis for the new technology that exploits the
capability of a photon to carry information and energy [1]. To
achieve this goal, new materials containing specific chromophores
with properties such as large nonlinear susceptibility, fast response,
easy preparation and handling should be developed to achieve the
Accordingly, compounds containing both donor (D) and acceptor
(A) components that exhibit interesting optical and spectral prop-
erties due to the intramolecular charge transfer (ICT) phenomenon
have attracted considerable attention in the literature [2]. The
electron-donating and electron-accepting substituents in these
molecules are connected through a
p-conjugated system of single
and double bonds. Typical representatives of this class of
compounds are properly substituted stilbenes or condensates of
benzaldehyde and nitrile of malonic acids. These molecules exhibit
various degree of flexibility in the ground and excited states that
could be correlated to radiation and radiationless processes. The
spectral properties of this ICT state have attracted considerable
attention both in photochemistry and photobiology because they
* Corresponding author. Tel.: þ421 2 54777404; fax: þ421 2 54775923.
E-mail address: upoldan@savba.sk (M. Danko).
0143-7208/$ e see front matter Ó 2011 Elsevier Ltd. All rights reserved.
doi:10.1016/j.dyepig.2011.07.011

1258
M. Danko et al. / Dyes and Pigments 92 (2012) 1257e1265
exhibit different degrees of charge transfer, which is susceptible
to some environmental parameters such as microviscosity and
micropolarity [1e7].
octyloxyl-triphenylamine-vinylene side chain were employed [16].
Multi-triarylamine substituted oligothiophenes were tested as
potential materials for organic solar cells [17].
Chalcones are another class of compounds with a strong elec-
tron donoreacceptor interactions, where in the donor and acceptor
moieties are linked by a keto e vinyl bridge [8e12]. The photo-
physical behavior of these conjugate intermolecular charge transfer
compounds has generated considerable attention due to potential
applications associated with the strong emission of laser and
fluorescent dyes and some theoretical problems such as the twisted
intramolecular charge transfer (TICT) state [2]. It was clearly
demonstrated that the luminescence properties of several chal-
cones with strong electron-donating and accepting substituents
strongly depend on the character of the substituent, the polarity of
the solvent and the temperature [8]. From the correlation of fluo-
rescence quantum yield with solvent polarity, a clear maximum
was observed indicating the presence of a negative solvatokinetic
effect with moderately increasing solvent polarity and a positive
solvatokinetic effect with highly polar solvents [8]. The spectral
properties of enone (chalcone) derivatives also depend on the
character of the bridge. The rigid structure of the enone bridge
favors radiative decay even in polar solvents. In contrast, enone
compounds with a free double bond have very low fluorescent
quantum yields, indicating that non-radiative decay is important. In
these compounds, the dissipation of electronic energy proceeds
through the rotation of structural units [9]. Recently, spectral and
photophysical properties of a new intramolecular charge transfer
(ICT) probe, namely 40-dimethylamino-2,5-dihydroxychalcone,
were explored [11]. It was observed that while the absorption
spectrum undergoes minor changes with increasing solvent
polarity, the fluorescence spectrum exhibits a distinct bath-
ochromic shift in the band position, and the fluorescence quantum
yield increases, reaches a maximum and then decreases with
increasing solvent polarity. The change in the dipole moment of
Dm ¼ 6.5D, based on LipperteMataga equation, is due to the redis-
tribution of the charges in the excited state.
In this paper, we report on the spectral characteristics of five
novel chalcones CH-1eCH-5 with diphenylaminophenyl substit-
uent linked by a propen-1-one bridge with substituted thiophene
and benzene unit. The goal of this study is to perform a thorough
spectral characterization of these systems and to compare spectral
properties of novel chalcone derivatives with a triphenylamino-
substituent as electron donor in solution with those in a polymer
matrix. A more complete understanding of photophysical and
electronic processes and sufficient spectral data will increase the
likelihood that these materials will find application in photonics.
2. Experimental
Silica gel 60 (230e400 mesh, Merck) was used for column
chromatography. 4-(N,N-diphenylamino)benzaldehyde, 1-(5-
methylthiophene-2-yl)etanone, 1-(5-bromothiophene-2-yl)etha-
none, 1-(2,20-dithiophene-5-yl)ethanone, 1-(5-((9H-fluoren-9-
ylidene)methyl)thiophen-2-yl)ethanone and 1-(4-bromophenyl)
etanone were purchased from Georganics Ltd. (http://www.
georganics.sk/) and was used as received. N,N-dimethylaniline
and N,N-dimethylformamide were purchased from SigmaeAldrich
and were used as received. Anthracene was zonnally refined
(Lachema n.e., Brno, CR). Methanol was in UV spectroscopy purity.
Cyclohexane (Merck), chloroform, tetrahydrofuran (Slavus, SR)
and acetonitrile (Merck) was spectroscopy grade purity.
Polymer films doped with chalcones were prepared by casting
from solution. Films of polystyrene (PS) (Chemische Werke Huels,
F.R.G.), poly(methylmethacrylate) (PMMA) (Diacon, ICI, England)
were prepared by casting of 1 ml chloroform solution of polymer
(5 g/100 ml) containing the respective amount of probe on a glass
plate (28 ꢁ 35 mm). The solvent was evaporated slowly. Films of
poly(vinylchloride) (PVC) (Neralit, Spolana Neratovice s.e., CR) were
prepared by casting from tetrahydrofuran solution as well. The
Recently, reports have appeared discussing the spectral and
photophysical characteristics of chalcone-analogue dyes containing
a butadiene bridge such as 1-(40-R-phenyl)-5-(40-dimethyl-ami-
nophenyl)-2,4-pentadien-1-one where R is H, Cl and OCH3 [10,12].
These dyes exhibit dual emission in polar solvents, which is
attributed to the population of a polar locally excited (LE) state and
a highly dipolar intramolecular charge transfer (ICT) state, similar
to what is observed in the case of chalcones with a single double
bond. The incorporation of a 2-pyridyl group in the chemical
structure of the chalcone analogue dye led to the design of
a potential optical sensor for probing the acidity of a medium and
the presence of metal cations [12].
concentration of probes in polymer film was 0.002 mol kgꢀ1
.
2.1. Synthesis
The structures of model chalcones CH-1m, CH-2m and chal-
cones CH-1eCH-5 are given in Scheme 1. The synthesis of CH-1m
and CH-2m was performed in two steps. In the first step 4-(N,N-
dimethylamino)benzaldehyde was prepared by reaction of dime-
thylaniline with dimethylformamide in the presence of phosphor-
ousoxytrichloride. In the second step corresponding benzaldehyde
reacted with the acetyl derivative to form chalcones. The details of
the synthesis are given below.
A dimethylaminophenyl chalcone was also used as a fluorescence
probe to characterize the polarity of the inner cavity of modified
montmorillonite demonstrating the importance of matching the
polarity of clay’s surface with that of a precursor polymer for the
preparation of polymereclay nanocomposites [13].
2.1.1. 4-(N,N-dimethylamino)benzaldehyde
Phosphorous oxychloride (11.3 g, 45 mmol) was added drop-
wise to the mixture of N,N-dimethylaniline (4.54 g, 37.5 mmol) and
N,N-dimethylformamide (5.48 g, 75 mmol) at 0e5 ꢂC. The reaction
mixture was stirred at room temperature for 2 h and at 65 ꢂC for
15 h. After cooling the reaction was basified with an aqueous
solution of sodium hydroxide (2 M). The formed solid residue was
filtered and product was recrystallized from diluted HCl, yielding
3.5 g (63%), m.p. 72e73 ꢂC (Ref. [18] 72e75 ꢂC).
The chalcones with a strong donating (D) and a strong accepting
(A) substituent with a p-conjugated spacer are under investigation as
potential materials for non-linear optics (NLO), because they are non-
symmetrical and exhibit high polarizability and hyperpolarizability.
In order to generate higher charge mobility, a dialkylamino func-
tional group was replaced with a diarylaminophenyl substituent for
chalcone dyes or in combination with a mono- or oligothiophene.
2.1.2. General procedure for synthesis of chalcones
A
simple 1-phenyl-(3-(4-diphenylamino)phenyl)prop-2-en-1-one
To 4-(N,N-dimethylamino)benzaldehyde or 4-(N,N-diphenyla-
mino)benzaldehyde (1 equivalent) and corresponding acetyl
derivative (1 equivalent) in ethanol was added aqueous solution of
sodium hydroxide (13 M). Reaction mixture was stirred at room
temperature for 4 h in the case of CH-1m and CH-2m and 3 days in
molecule was used as an efficient organic light color conversion
material for a white LED [14]. Triphenylamine-based dyes containing
thiophene units were utilized in dye-sensitized solar cells [15]. For
polymer solar cells and field effect transistors, polythiophenes with an

M. Danko et al. / Dyes and Pigments 92 (2012) 1257e1265
1259
Scheme 1. Chemical structures and names of the investigated chalcones.
the case of CH-1eCH-5. The precipitated product was filtered.
The crude product was purified by crystallization or column
chromatography.
1H NMR (400 MHz, CDCl3, ppm)
d
: 3.05 (s, 6H, 2 ꢁ CH3),
6.68e6.71 (d, 2H, J ¼ 8.8 Hz, PheN<), 7.31e7.36 (d, 1H, J ¼ 15.4 Hz,
eCH ¼ CHeCO), 7.45e7.60 (m, 3H PheCO þ 2H PheCH],
J ¼ 8.8 Hz), 7.77e7.82 (d, 1H, J ¼ 15.4 Hz, PheCH]), 7.99e8.02 (d,
2H, J ¼ 8.8 Hz, PheCO). 1H NMR was the same as for chalcone
reported in [13].
2.1.3. 3-(4-(N,N-Dimethylamino)phenyl)-1-phenylprop-2-en-1-one
(CH-1m)
For reaction 4-(N,N-dimethylamino)benzaldehyd (1.77 g,
10.7 mmol) and acetophenone (1.3 g,10.8 mmol) in ethanol (15 mL)
was used. The crude product was recrystallized from ethanol,
yielding 0.63 g of yellow crystals (24%), m.p. 111e113 ꢂC (Ref. [13]
110.5e111.5 ꢂC).
2.1.4. 3-(4-(N,N-Dimethylamino)phenyl)-1-(4-nitrophenyl)prop-2-
en-1-one (CH-2m)
For reaction 4-(N,N-dimethylamino)benzaldehyde (1.77 g,
10.7 mmol) in ethanol (25 mL) and 4-nitroacetophenone (1.78 g,

1260
M. Danko et al. / Dyes and Pigments 92 (2012) 1257e1265
10.8 mmol) in diethylether (25 mL) was used. The crude product
was purified by recrystallization from ethanol, yielding 0.25 g (8%)
of red crystals, m.p. 219e220 ꢂC.
13C NMR (75 MHz, CDCl3, ppm)
d: 118.4, 121.5, 124.1, 124.2, 125.5,
126.3 (12 ꢁ d), 127.6 (s), 128.2, 129.5, 129.7, 132.1 (8 ꢁ d), 136.5 (s),
143.6 (d), 144.1, 145.4, 146.7, 150.2 (5 ꢁ s), 181.5 (s, CO).
UV (CHCl3, 25 ꢂC, nm) lmax: 267, 350, 447.
FT-IR (KBr) n .
: 1653 (CO) cmꢀ1
1H NMR (400 MHz, CDCl3, ppm)
d
: 3.07 (s, 6H, 2 ꢁ CH3),
Elem. Anal.: For C29H21NOS2 required C75.13; H4.57; N3.02%
Found: C76.28; H4.62; N3.11%.
6.69e6.72 (d, 2H, J ¼ 9.3 Hz, PheN<), 7.24e7.29 (d, 1H, J ¼ 15.4 Hz,
eCH]), 7.55e7.58 (d, 2H, J ¼ 9.3 Hz, PheCH]), 7.80e7.85 (d, 1H,
J ¼ 15.4 Hz, eCHe), 8.10e8.13 (d, 2H, J ¼ 9.3 Hz, PheCO), 8.32e8.35
(d, 2H, J ¼ 9.3 Hz, PheNO2).
2.1.8. 1-(5-((9H-Fluoren-9-ylidene)methyl)thiophene-2-yl)-3-(4-
(N,N-diphenylamino)phenyl)prop-2-en-1-one (CH-4)
For reaction 4-(N,N-difenylamino)benzaldehyd (90.4 mg,
0.331 mmol) and 1-(5-((9H-fluoren-9-ylidene)methyl)thiophen-2-
yl)ethanone (100 mg, 0.331 mmol) in ethanol (30 mL) was used.
Crude product was purified by column chromatography (hex-
ane:ethylacetate, 95:5), yielding 70 mg of red crystals (38%), m.p.
201e206 ꢂC.
13C NMR (100 MHz, DMSO, ppm)
d: 40.3, 112.3, 116.0, 122.0,
124.0, 129.7, 131.8, 143.9, 145.0, 147.3, 149.9, 188.0 (C]O).
FT-IR (KBr)
n
: 1647 (CO) cmꢀ1
.
Elem. Anal.: For C17H16N2O3 required C68.90; H5.44; N9.45%
Found: C69.31; H5.53; N9.49%.
2.1.5. 1-(5-Methylthiophene-2-yl)-3-(4-(N,N-diphenylamino)
phenyl)-prop-2-en-1-one (CH-1)
UV (CH2Cl2, 25 ꢂC, nm) lmax: 232, 264, 299, 451.
1H NMR (300 MHz, CDCl3, ppm)
d
: 7.04 (d, J ¼ 8.7 Hz, 2H),
For reaction 4-(N,N-diphenylamino)benzaldehyde (0.5 g,
3.5 mmol) and 1-(5-methylthiophene-2-yl)etanone (0.97 g,
3.5 mmol) in ethanol (50 mL) was used. Crude product was
crystallized from methanol with yielding 0.79 g (57%), m.p.
126e132 ꢂC.
7.22e7.09 (m, 7H), 7.40e7.29 (m, 7H), 7.56e7.50 (m, 5H), 7.75e7.67
(m, 5H), 7.87e7.83 (m, 1H).
13C NMR (75 MHz, CDCl3, ppm)
d: 118.4, 121.5, 124.1, 124.2, 125.5,
126.3 (22 ꢁ d), 127.6 (s), 128.2, 129.5, 129.7, 132.1 (8 ꢁ d), 136.5 (s),
143.6 (d), 144.1, 145.4, 146.7, 150.2 (5 ꢁ s), 181.5 (s, CO).
UV (CH2Cl2, 25 ꢂC, nm) lmax: 246, 295; 361, 421.
FT-IR (KBr) n .
: 1653 (CO) cmꢀ1
1H NMR (300 MHz, CDCl3, ppm)
d: 2.59 (s, 3H, CH3), 7.06e7.04
Elem. Anal.: For C39H27NOS required C83.99; H4.88; N2.51%
Found: C86.50; H4.99; N2.58%.
(m, 2H), 7.13 (t, J ¼ 3.9 Hz, 2H), 7.19e7.17 (m, 2H), 7.21e7.20 (m, 2H),
7.21e7.20 (m, 4H), 7.33 (t, J ¼ 3.9 Hz, 2H), 7.37 (t, J ¼ 3.9 Hz, 2H), 7.51
(d, J ¼ 4.2 Hz, 1H), 7.80 (d, J ¼ 7.8 Hz, 1H).
2.1.9. 1-(4-Bromophenyl)-3-(4-(N,N-diphenylamino)phenyl)prop-
2-en-1-one (CH-5)
13C NMR (75 MHz, CDCl3, ppm)
d: 16.1 (q, CH3), 121.6 (d), 121.9
(s), 124.0, 125.1, 125.4, 126.3, 129.1, 129.6 (15 ꢁ d), 131.3, 143.2
For reaction 4-(N,N-diphenylamino)benzaldehyde (273 mg,
1 mmol) and 1-(4-bromophenyl)etanone (200 mg, 1 mmol) in
ethanol (50 mL) was used. Product was re-crystallized from
methanol, yielding 250 mg of white crystals (55%), m.p.131e134 ꢂC.
UV (CH2Cl2, 25 ꢂC, nm) lmax: 262, 294, 425.
(2 ꢁ d), 146.1, 146.8, 153.3 (5 ꢁ s), 181.6 (s, CO).
FT-IR (KBr) n .
: 1653 (CO) cmꢀ1
Elem. Anal.: For C26H21NOS required C78.95; H5.35; N3.54%
Found: C80.64; H5.49; N3.59%.
1H NMR (300 MHz, CDCl3, ppm)
d: 7.03 (d, J ¼ 4.2 Hz, 2H), 7.12 (t,
2.1.6. 1-(5-Bromothiophene-2-yl)-3-(4-(N,N-diphenylamino)
phenyl)prop-2-en-1-one (CH-2)
J ¼ 3.9 Hz, 2H), 7.15 (d, J ¼ 4.2 Hz, 4H), 7.34e7.30 (m, 5H, H-1,
phenyl), 7.48 (d, J ¼ 4.5 Hz, 2H), 7.63 (d, J ¼ 4.2 Hz, 2H), 7.77 (d,
J ¼ 7.5 Hz, 1H), 7.87 (d, J ¼ 4.2 Hz, 2H).
For reaction 4-(N,N-diphenylamino)benzaldehyde (266 mg,
0.975 mmol) and 1-(5-bromothiophene-2-yl)ethanone (200 mg,
0.975 mmol) in ethanol (20 mL) was used. Crude product was
purified by column chromatography on silikagel with mixture
hexane:ethylacetate, 99:1 as eluent, yielding 130 mg of yellow
crystals (29%), m.p. 187e188 ꢂC (methanol).
13C NMR (75 MHz, CDCl3, ppm)
d: 118.7, 121.4, 124.2, 125.5
(9 ꢁ d), 127.5, 129.3 (4 ꢁ s), 129.5, 129.8, 129.9, 131.8 (10 ꢁ d), 137.4,
145.2 (2 ꢁ s), 146.7 (s), 189.3 (s, CO).
FT-IR (KBr) n .
: 1652 (CO) cmꢀ1
Elem. Anal.: For C27H20BrNO required C71.37; H4.44; N3.08%
Found: C73.51; H4.57; N3.18%.
UV (CH2Cl2, 25 ꢂC, nm) lmax: 297, 436.
1H NMR (300 MHz, CDCl3, ppm)
d
: 7.02 (d, J ¼ 8.7 Hz, 2H),
7.19e7.09 (m, 8H), 7.34e7.28 (m, 4H), 7.47 (d, J ¼ 8.7 Hz, 2H), 7.56 (d,
2.2. Spectral measurements
J ¼ 4.2 Hz, 1H), 7.79 (d, J ¼ 15.6 Hz, 1H).
13C NMR (75 MHz, CDCl3, ppm)
d
: 117.5, 121.3 (2 ꢁ d), 122.2 (s),
NMR spectra (1H at 300 and/or 400 MHz, 13C at 75 and/or
100 MHz) were obtained in CDCl3 and DMSO using a VARIAN
spectrometer with tetramethylsilane (TMS) as the internal stan-
dard. Chemical shifts are reported in parts per million (ppm).
Coupling constants are reported in Hertz (Hz). Splitting patterns are
designated as s: singlet, d: doublet, t: triplet m: multiplet. Reactions
and the collected fraction samples were monitored by TLC (Merck
60 F254 silica gel). Visualization was afforded using a UV hand lamp
with 254 nm wavelength light. Melting points were recorded on
a Kofler block and are uncorrected. Infrared spectra (KBr) were
determined on a PerkineElmer 1600 FT-IR and Nicolet 8700
(Thermo, USA) systems. Elemental analyses were measured by
means of Carlo Erba Elemental Analyzer 1108.
UVeVIS absorption spectra were obtained on a UV 1650PC
spectrometer (Shimadzu, Japan). Emission spectra were recorded
on a RF-5301PC spectrofluorophotometer (Shimadzu, Japan).
Solution fluorescence was measured in a 1 cm cuvette using the
right angle arrangement. Polymer film fluorescence was measured
using the front face arrangement in a solid sample holder.
124.2, 125.5, 127.2, 129.5, 129.8 (14 ꢁ d), 131.2, 144.4 (2 ꢁ d), 146.7
(2 ꢁ s), 147.49 (2 ꢁ s), 150.4 (s), 180.8 (s, CO).
FT-IR (KBr) n .
: 1652 (CO) cmꢀ1
Elem. Anal.: For C25H18BrNOS required C65.22; H3.94; N3.04%.
Found: C67.21; H4.01; N3.14%.
2.1.7. 1-(2,20-Dithiophene-5-yl)-3-(4-(N,N-diphenylamino)phenyl)
prop-2-en-1-one (CH-3)
For reaction 4-(N,N-diphenylamino)benzaldehyde (150 mg,
0.55 mmol) and 1-(2,20-dithiophene-5-yl)ethanone (114 mg,
0.55 mmol) in ethanol (15 mL) was used. Crude product was crys-
tallized from mixture methanolewater, yielding 120 mg of yellow
crystals (47%), m.p. 186e189 ꢂC.
UV (CH2Cl2, 25 ꢂC, nm) lmax: 234, 300, 441.
1H NMR (300 MHz, CDCl3, ppm)
d
: 7.03 (d, J ¼ 8.7 Hz, 2H),
7.11e7.08 (m, 2H), 7.16e7.14 (m, 5H), 7.24e7.21 (m, 1H), 7.34e7.28
(m, 7H), 7.49 (d, J ¼ 8.7 Hz, 2H), 7.73 (d, J ¼ 3.9 Hz, 1H), 7.80 (d,
J ¼ 15.6 Hz, 1H).

M. Danko et al. / Dyes and Pigments 92 (2012) 1257e1265
1261
Table 1
The quantum yield of fluorescence of the chalcones was deter-
mined in solution and in polymer films using anthracene as the
standard in the respective medium, using the quantum yield of 0.25
for anthracene in cyclohexane [19]. The quantum yield of anthra-
cene fluorescence in different media was determined by comparing
the fluorescence of anthracene in cyclohexane and various other
media. It was found to be 0.22 in acetonitrile, 0.20 in methanol, and
0.11 in chloroform. In polymer matrices, the quantum yield was
assumed to be 0.20 in PMMA, 0.16 in PS and 0.11 in PVC. The
quantum yield in solution and film was corrected to different
absorptions at the excitation wavelength [20]. The fluorescence
spectra were obtained by exciting at the maximum of the longest
wavelength absorption band.
The fluorescence lifetime measurements were performed on a LIF
200 (Lasertechnik Ltd., Berlin, F.R.G.), which operates as a strobo-
scope. The excitation source is a nitrogen laser emitting at 337 nm
and the emission is selected by a cut-off filter. The output signal of the
Box Car Integrator was digitized and transferred to a PC using
a home-made program. The fluorescence decay curves were evalu-
ated by a simple phase plane method [21], using program designed
by J. Snyder discussed in reference [22]. The standard deviation,
derived from equation: G1/2 ¼ S((Iexp ꢀ Icalc)2/n)1/2, where Iexp and
Icalc are intensity of emission experimental and calculated respec-
tively, is used to determine whether the decay is monoexponential. It
is assumed that the decay curve satisfies the monoexponential
condition when G1/2 is lower than 5%. Alternatively, the fitting of the
fluorescence decay curves to a model of biexponential decay was
performed using an adapted FluoFit MatLab package [23].
Spectral properties of model chalcones CH-1m and CH-2m in solution and polymer
matrices.
Mediuma
lA
(nm)
log
3
lF
(nm)
Dne
Ff
sg
(ns)
G1/2,h
(%)
b
c
d
(cmꢀ1
)
(2E)-3-[4-(N,N-dimethylamino)phenyl]-1-phenylprop-2-en-1-one (CH-1m)
MeOH
CHCl3
PS
PMMA
PVC
417
415
403
407
422
4.23
4.43
4.28
4.24
4.17
542
510
477
483
512
5502
4489
3850
3866
4177
0.040
0.165
0.080
0.200
0.407
0.9
1.5
1.8
4.4
2.8
2.9
(2E)-3-[4-(N,N-dimethylamino)phenyl]-1-(4-nitrophenyl)prop-2-en-1-one
(CH-2m)
MeOH
CHCl3
PS
PMMA
PVC
444
447
441
443
457
3.92
4.81
4.55
4.31
4.29
526
520
551
554
565
3511
3141
4527
4497
4183
0.020
0.008
0.528
0.240
0.347
2.6
2.0
2.0
3.3
3.7
4.3
a
Medium: MeOH e methanol, CHCl3 e chloroform, PS e polystyrene, PMMA e
poly(methylmethacrylate), PVC e poly(vinylchloride).
b
Maximum of the longest wave absorption.
Molar decadic extinction coefficient calculated from
c
3
in L molꢀ1 cmꢀ1 or
kg molꢀ1 cmꢀ1
.
d
e
f
Maximum of fluorescence band.
Stokes shift.
Quantum yield based on anthracene.
Life time of fluorescence.
Error of lifetime determination.
g
h
absorption band. The Stokes shift is larger in methanol (5500 cmꢀ1
)
than it is in PS and PMMA (3800 cmꢀ1). The quantum yield of
fluorescence of CH-1m is comparable with that of anthracene in
chloroform. In addition, when incorporated into the PVC polymer
3. Results and discussion
As shown in Fig. 1, the absorption spectra of the model chalcone
CH-1m containing an electron-donating group exhibits the longest
wavelength band at approximately 410 nm being at 417 nm in polar
methanol and at 403 nm in non-polar PS. This band is relatively
strong in all media, with log > 4 (Table 1). The fluorescence of the
3
CH-1m is red-shifted up to 540 nm in methanol. In non-polar PS,
the fluorescence maximum is only at 480 nm. Clearly, the fluores-
cence maximum of CH-1 is more sensitive to the medium than the
Fig. 1. Absorption and fluorescence spectra of model chalcones CH-1m and CH-2m in
chloroform, methanol at 10ꢀ5 mol Lꢀ1 and PS at 0.002 mol kgꢀ1. Excitation wave-
lengths for CH-1m were 415 nm in MeOH and CHCl3 and 403 nm in PS. Excitation
wavelengths for CH-2m were 445 nm in all media.
Fig. 2. Changes in fluorescence spectra of CH-1m (3-[4-(N,N-dimethylamino)phenyl]-
1-phenylprop-2-en-1-one) measured at 10ꢀ5 mol Lꢀ1 in different solvent mixtures
chloroform/methanol expressed in emission maxima shift and SterneVolmer equation.

1262
M. Danko et al. / Dyes and Pigments 92 (2012) 1257e1265
Fig. 5. Absorption and fluorescence spectra of CH-4 (1-(5-((9H-Fluoren-9-ylidene)
methyl)thiophene-2-yl)-3-(4-(N,N-diphenylamino)-phenyl)prop-2-en-1-one) and CH-
5 (1-(4-Bromophenyl)-3-(4-(N,N-diphenylamino)phenyl)prop-2-en-1-one) in chloro-
form at 10ꢀ5 mol Lꢀ1. Excitation wavelengths for chalcones were the same as its
absorption maxima listed in Table 2.
acetonitrile results in the enhancement of fluorescence (Fig. 3). The
acetonitrile solvent does not contain groups capable of hydrogen
bounding, so a negative solvatochromic effect is observed for
CH-1m [8]. The lifetime of fluorescence was determined in polymer
matrices only and is approximately 1 ns in PS and slightly longer in
PMMA and PVC.
Fig. 3. Changes in fluorescence spectra of CH-1m (3-[4-(N,N-dimethylamino)phenyl]-
1-phenylprop-2-en-1-one) measured at 10ꢀ5 mol Lꢀ1 in different solvent mixtures
chloroform/acetonitrile expressed in emission maxima shift and SterneVolmer
equation.
matrix, the greatest increase in quantum yield is observed (w0.4).
The addition of polar methanol quenches the fluorescence of CH-
1m in a SterneVolmer like manner (Fig. 2) and red-shifts the
fluorescence maximum. In contrast, the addition of polar aprotic
Fig. 4. Absorption and fluorescence spectra of CH-1 (3-(4-(N,N-diphenylamino)
phenyl)-1-(5-methylthiophene-2-yl)prop-2-en-1-one, CH-2 (1-(5-Bromothiophene-2-
yl)-3-(4-(N,N-diphenylamino)phenyl)prop-2-en-1-one) and CH-3 (1-(2,20-Dithio-
phene-5-yl)-3-(4-(N,N-diphenylamino)phenyl)prop-2-en-1-one) in chloroform at
10ꢀ5 mol Lꢀ1. Excitation wavelengths for chalcones were the same as its absorption
maxima listed in Table 2.
Fig. 6. Absorption and fluorescence spectra of CH-1 (3-(4-(N,N-diphenylamino)
phenyl)-1-(5-methylthiophene-2-yl)prop-2-en-1-one) in chloroform, cyclohexane and
acetonitrile at concentration 10ꢀ5 mol Lꢀ1 with excitation wavelengths 423, 413 and
409 nm, respectively.

M. Danko et al. / Dyes and Pigments 92 (2012) 1257e1265
1263
For CH-2m, with an electron-donating dimethylamino group
on one end and electron-accepting nitro on the other end, the
maximum of the longest wavelength absorption band is red-
shifted to 445 nm in all media (Fig. 1, Table 1). The fluorescence
of CH-2m in polymer matrices is red-shifted even more to 550 nm
compared to the solution value of 520 nm. The Stokes shift lies in
the range of 3000e4500 cmꢀ1, with a larger increase observed for
polymer matrices. The quantum yield of fluorescence for CH-2m is
low in solution even in moderately polar chloroform, as was
observed previously [8]. In contrast, the fluorescence of CH-2m is
fairly intense when incorporated into polymer matrices. The life-
time of CH-2m is about 2 ns in polymer matrices. The intense
fluorescence of CH-2m might be due either to the suitable degree
of charge transfer, which still supports the radiation deactivation
or because of the stabilization of the structure in the polymer
(hindering some vibrations), which again supports radiation
deactivation.
Comparison of spectral data of model chalcones CH-1m and
CH-2m shows that the range of spectral shifts is larger for CH-1m
than is observed for CH-2m. For both probes, the quantum yield is
larger in the solid matrices than in solution. Clearly, the additional
substitution of CH-1m with a strong electron-withdrawing nitro
group resulting in CH-2m does not generate more intense fluo-
rescence in solution [7], but it does yield a more intense fluores-
cence when doped in a polymer matrix.
The absorption spectra of novel chalcones CH-1eCH-5 exhibit
the longest wavelength band in the range of 410e450 nm in solu-
tions (Figs. 4e6, Table 2) as well as in polymer matrices (Fig. 7,
Table 3). In the absorption spectra of CH-1 in non-polar cyclo-
hexane and in polar methanol and acetonitrile, the longest
Fig. 7. Absorption and fluorescence spectra of CH-1 (3-(4-(N,N-diphenylamino)phenyl)-
1-(5-methylthiophene-2-yl)prop-2-en-1-one) in chloroform (at c ¼ 10ꢀ5 mol Lꢀ1, poly-
styrene (PS) and poly(vinylchloride) at c ¼ 0.002 mol kgꢀ1. Excitation wavelengths were
423 nm in CHCl3, 415 nm in PS and 427 nm in PVC.
Table 2
Spectral properties of substituted chalcones CH-1eCH-5 in various solvents.
Dnd
Fe
sf
(ns)
a
b
c
Sample
lA
log
3
lF
(nm)
(nm)
(cmꢀ1
)
wavelength is observed as a shoulder on the more intense
absorption band around 350 nm. For CH-1eCH-5, the longest
wavelength band has a high intensity in all media, and exhibits
Chloroform
CH-1
CH-2
CH-3
CH-4
423
439
444
452
429
4.19
4.57
4.59
4.64
4.57
538
551
550
574
545
5053
4630
4341
4702
4961
0.49
0.36
0.47
0.07
0.37
3.6
3.1
2.0
1.5
3.4
log
of more than 4.0 (see Tables 2 and 3).
3
CH-5
Table 3
Cyclohexane
Spectral properties of substituted chalcones CH-1eCH-5 in polymer matrices.
CH-1
413
352
430
433
433
410
3.89
4.39
4.49
4.53
4.61
4.47
440s, 463
405s, 419
454, 476s
454, 480s
487, 512s
419s, 446, 472s
1486
0.016
0.020
0.084
0.086
0.002
0.069
1.8
a
b
Sample
lA (nm)
log
3
lFc (nm)
Dnd (cmꢀ1
)
Fe
sf (ns)
CH-2
CH-3
CH-4
CH-5
1229
1068
2501
1968
0.8
0.6
1.4
1.3
Polystyrene
CH-1
CH-2
CH-3
CH-4
359, 415s
437
443
449
427
4.26
4.71
4.44
4.43
4.42
428s, 483
519
491s, 517
548
732
3615
2206
4024
3811
0.024
0.077
0.028
0.029
0.093
2.2
2.1
1.2
1.2
2.4
Acetonitrile
CH-1
CH-5
510
409
352
426
433
441
416
4.05
4.30
4.36
4.56
4.58
4.43
448, 553
530
461, 583
589s
502, 536
468, 558
2128
0.0200
0.0160
0.0060
0.0080
0.0002
0.0030
0.6
Poly(methylmethacrylate)
CH-2
CH-3
CH-4
CH-5
1782
6117
2755
2671
0.6
0.4
2.0
2.0
CH-1
CH-2
CH-3
CH-4
CH-5
299, 412s
433
437
444
416
4.34
4.39
4.41
4.41
4.65
499
526
532
558
517
4232
4083
4086
4601
4696
0.041
0.064
0.058
0.028
0.102
3.9
2.7
1.3
1.6
2.7
Methanol
CH-1
435s
356
433
441
453
424
523
440
504
502
502
477
0.0058
0.0020
0.0068
0.0020
0.0004
0.0016
3.6
Poly(vinylchloride)
4.34
4.28
4.50
4.49
4.34
CH-1
CH-2
CH-3
CH-4
CH-5
362, 427s
4.13
4.23
4.27
4.58
4.30
436s, 513
548
556
544s, 598
542
4834
4224
4138
3169
4486
0.088
0.297
0.036
0.020
0.248
3.8
2.9
1.5
1.7
3.5
CH-2
CH-3
CH-4
CH-5
3253
2755
2155
2621
2.2
1.5
6.0
5.6
445
452
464
436
a
a
Maximum of the longest wave absorption (s means shoulder).
Maximum of the longest wave absorption (s means shoulder).
b
c
d
e
f
b
c
d
e
f
Molar decadic extinction coefficient calculated from
Maximum of fluorescence band (s means shoulder).
Stokes shift.
3
in L molꢀ1 cmꢀ1
.
Molar decadic extinction coefficient calculated from
Maximum of fluorescence band (s means shoulder).
Stokes shift.
Quantum yield of fluorescence based on anthracene.
Life time of fluorescence.
3 .
in kg molꢀ1 cmꢀ1
Quantun yield of fluorescence based on anthracene.
Life time of fluorescence.

1264
M. Danko et al. / Dyes and Pigments 92 (2012) 1257e1265
The fluorescence of the CH-1eCH-5 is red-shifted up to 575 nm
The fluorescence maximum in polymer matrices is red-shifted
as well (Table 3). Often several fluorescence bands (usually 2) are
observed in PVC. For CH-4 the maximum of fluorescence lies at
598 nm in the PVC matrix. The fluorescence of CH-1eCH-5 in
polymer matrices is less intense than it is in chloroform but more
intense than it is when other solvents are used. The highest fluo-
rescence intensity in polymer matrices is observed in poly(vinyl-
chloride). Clearly, the presence of chlorine atoms (possible heavy
atoms) leads to a more effective radiation deactivation of the
excited state or a decrease in the rate of radiationless relaxation of
the excited state for these chalcone derivatives. It appears that the
chlorine atom supports radiation deactivation and has an effect
opposite to that of the polarity of the solvent.
In some media the less intense fluorescence is observed for
CH-4 having the complex substituent 5-((9H-fluoren-9-ylidene)
methyl)thiophene. It might exhibit an increased rate of radiation-
less process in some media probably because it has got more
flexible structure. Ratio of quantum yields of CH-5 and CH-4 is
about 5 in chloroform. It is lower for PS, PMMA (about 3), but larger
for PVC (about 12). The comparison of quantum yields of novel
chalcones CH-1eCH-5 in solution and in the polymer matrices
indicates some fixation of structure in polymer matrices leading to
lower rate of radiationless deactivation. The quantum yields data
for complex CH-4 confirms this conclusion in some extent.
in chloroform and the Stokes shift is large e up to 5000 cmꢀ1 for
CH-1 (Table 2). The fluorescence quantum yield for all chalcones
except CH-4 is comparable or even higher than that of anthracene
in chloroform. In non-polar cyclohexane, the maximum of fluo-
rescence is less red-shifted than in chloroform and exhibits some
vibrational structure. The Stokes shift lies in the range of
1500e2500 cmꢀ1. The fluorescence of CH-1eCH-5 in cyclohexane
is less intense up to 30 times. A similar but more pronounced effect
is observed with polar solvents such as acetonitrile and methanol
(decrease in intensity of approximately 250 times). One would
expect that the maxima of fluorescence bands in polar solvents are
more red-shifted than in chloroform. However, we observed that
the fluorescence maximum in methanol lies in the range of 440 up
520 nm. Further, the fluorescence spectra of CH-1eCH-5 in aceto-
nitrile show some structure e one band at approximately 460 nm
and second one at 550 nm. A red-shifted fluorescence band, larger
than that observed in chloroform (589 nm), is observed for CH-3 in
acetonitrile. In this case, the Stokes shift is a rather large 6117 cmꢀ1
.
Clearly, the fluorescence of chalcones CH-1eCH-5 is influenced
by solvents in a similar pattern as was reported in paper [8]. In non-
polar solvents such as cyclohexane, the fluorescence is rather weak.
In moderately polar solvents such as chloroform, the intensity of
fluorescence increases, indicating that a negative solvatokinetic
effect is taking place. In strong polar solvents, the fluorescence is
strongly quenched due to large degree of intramolecular charge
transfer (ICT), which causes an increase in the rate of radiationless
relaxation of an excited state, indicating that the positive sol-
vatokinetic effect is taking place.
The comparison of the solvent effects on the properties of
CH-1m and CH-1 demonstrates that there is a difference in
behavior. Both chalcones are quenched by polar methanol (Figs. 2
Fig. 8. Changes in fluorescence spectra of CH-1 (3-(4-(N,N-diphenylamino)phenyl)-1-
(5-methylthiophene-2-yl)prop-2-en-1-one) measured at 10ꢀ5 mol Lꢀ1 in different
solvent mixtures chloroform/methanol expressed in emission maxima shift and
SterneVolmer equation.
Fig. 9. Changes in fluorescence spectra of CH-1 (3-(4-(N,N-diphenylamino)phenyl)-1-
(5-methylthiophene-2-yl)prop-2-en-1-one) measured at 10ꢀ5 mol Lꢀ1 in different
solvent mixtures chloroform/acetonitrile expressed in emission maxima shift and
SterneVolmer equation.

M. Danko et al. / Dyes and Pigments 92 (2012) 1257e1265
1265
and 8) with a large red-shift in the fluorescence maximum. The
Acknowledgement
quenching of CH-1 (KSV ¼ 6.1 L molꢀ1) is about ten times more
efficient than that of CH-1m (KSV ¼ 0.49 L molꢀ1). The efficiency
of quenching of CH-1 in acetonitrile (KSV ¼ 0.61 L molꢀ1) is
substantially lower than that of methanol (KSV ¼ 6.1 L molꢀ1) and
comparable with that of CH-1m quenched with methanol
(KSV ¼ 0.49 L molꢀ1). Methanol is an efficient quencher of CH-1
due to the effect of polarity and hydrogen bond formation. In
contrast, acetonitrile quenches the fluorescence of CH-1 (Figs. 3
and 9), while it enhances fluorescence of CH-1m. It follows that
for the system CH-1m/chloroform/acetonitrile, a negative sol-
vatokinetic effect is observed, while for the system CH-1/chlo-
roform/acetonitrile, a positive solvatokinetic effect takes place.
The lifetime of fluorescence in all media used in this study lies
in the range of 0.5e6 ns. There is no obvious influence of the
solvent or the polymer matrix on the lifetime of fluorescence.
Therefore, fluorescence lifetime cannot be used to monitor the
effect of the medium.
Authors thank grant agency VEGA for support of projects 2/
0097/09 and 1/0660/11. This publication is the result of the project
implementation: Centre for materials, layers and systems for
applications and chemical processes under extreme conditions
Stage II supported by the Research & Development Operational
Programme funded by the ERDF.
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