3-(7-Dimethylamino)coumarin N-phenylsemicarbazones in solution and polymer matrices: Tuning their fluorescence via para-phenyl substitution

Article abstract of DOI:10.1016/j.saa.2014.01.127

The photo-physical properties of five new para-phenyl substituted derivatives of 3-(7-dimethylamino)coumarin N-phenylsemicarbazone with various electron-withdrawing substituents R (RF, Br, CF₃, CN or NO ₂) in the para-position on the phenyl ring were investigated in solvents and in polymer matrices. Tuning their fluorescent properties via para-substitution is discussed in terms of Twisted Intra-molecular Charge-Transfer (TICT) state formation, specific solute-solvent interactions (hydrogen bonding), fluorescent H-aggregates formation, and the solvent polarity and polymer matrix effects.

Full text of DOI:10.1016/j.saa.2014.01.127

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
3-(7-Dimethylamino)coumarin N-phenylsemicarbazones in solution
and polymer matrices: Tuning their fluorescence via para-phenyl
substitution
b
a
a
a
ˇ a,
ˇ
⇑
Marek Cigán , Martin Danko , Jana Donovalová , Jan Gašpar , Henrieta Stankovicová ,
a
´
ˇ b
Anton Gáplovsky , Pavol Hrdlovic
a Faculty of Natural Sciences, Institute of Chemistry, Comenius University, Mlynská dolina CH-2, SK-842 15 Bratislava, Slovakia
b Polymer Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 845 41 Bratislava, Slovakia
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
ꢀ
ꢀ
ꢀ
ꢀ
ꢀ
Five new 3-(7-dimethylamino)
coumarin N-phenylsemicarbazones
were synthesized.
Tuning their fluorescent properties
via para-phenyl substitution was
investigated.
Solvent polarity (TICT state
formation, hydrogen bonds) and
polymer matrix effects are discussed.
Unusual formation of fluorescent
H-aggregates in both protic and
aprotic polar solvents was observed.
Several coumarin-semicarbazones
qualify as laser dyes in the given
medium.
a r t i c l e i n f o
a b s t r a c t
Article history:
The photo-physical properties of five new para-phenyl substituted derivatives of 3-(7-dimethyl-
amino)coumarin N-phenylsemicarbazone with various electron-withdrawing substituents R (R@F, Br,
CF3, CN or NO2) in the para-position on the phenyl ring were investigated in solvents and in polymer
matrices. Tuning their fluorescent properties via para-substitution is discussed in terms of Twisted
Intra-molecular Charge-Transfer (TICT) state formation, specific solute–solvent interactions (hydrogen
bonding), fluorescent H-aggregates formation, and the solvent polarity and polymer matrix effects.
Ó 2014 Elsevier B.V. All rights reserved.
Received 31 October 2013
Received in revised form 20 January 2014
Accepted 26 January 2014
Available online 10 February 2014
Keywords:
3-(7-Dimethylamino)coumarin N-
phenylsemicarbazones
Tuning of fluorescent properties
Para-phenyl substitution
Solvent polarity and polymer matrix effects
TICT excited state
Fluorescent H-aggregates
Introduction
⇑
Corresponding author. Tel.: +421 2 60296306; fax: +421 2 60296342.
ˇ
E-mail addresses: cigan@fns.uniba.sk (M. Cigán), upoldan@savba.sk (M. Danko),
The fluorescence of 7-dialkylaminocoumarins is strongly
dependent on the polarity, hydrogen bonding ability, pH, the
donovalova@fns.uniba.sk (J. Donovalová), gaspar@fns.uniba.sk (J. Gašpar), gaplovsky@
ˇ
fns.uniba.sk (A. Gáplovsky´), upolhrdl@savba.sk (P. Hrdlovic).
http://dx.doi.org/10.1016/j.saa.2014.01.127
1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

ˇ
M. Cigán et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
37
presence of quest anions, various metal ions, biologically impor-
tant compounds, chemical warfare agents and the micro-viscosity
or rotational hindrance in their local environment [1–26]. More-
over, this class of compounds has received considerable attention
due to their ability to lase in the blue–green region [5,17]. The
photo-physical properties of these dyes depend on the nature
and pattern of substitution of the nitrogen atom of the amino
group and appropriate substituents at the 3-, 4-, and 6- positions
of the coumarin moiety.
In our recent study [27], the photophysical properties of
7-(dimethylamino)coumarin-3-carbaldehyde and its phenylsemic-
arbazone were investigated in solvents of various polarity and in
differing solvent mixtures. The different fluorescent quantum yield
according to the literature [31]. The structure of the prepared alde-
hyde was proven by 1H NMR spectra.
General procedure for the synthesis of 4-(4-substituted-
phenyl)semicarbazones
Semicarbazides were prepared according to a modified proce-
dure from the literature [32] (Scheme S1). Phenyl chloroformate
(20 mmol) was added dropwise to a mixture of aniline (20 mmol),
pyridine (20 mmol) and dry CH2Cl2 (40 mL) in an ice-water bath
and stirred at room temperature for 18 h. The mixture was then
evaporated under reduced pressure and the residue was poured
into saturated NaCl for salting out. The precipitate was filtered,
dried, and stirred in hydrazine hydrate (80%, 10 ml) at room tem-
perature for 4 h and then filtered off and recrystallized from
ethanol.
(UF) behaviour of these coumarins in highly polar solvents was dis-
cussed in terms of TICT state formation and the specific solute–sol-
vent interactions. 7-(dimethylamino)coumarin-3-carbaldehyde
exhibits a strong solvent effect in polar solvents due to the forma-
tion of a non-fluorescent TICT state and could prove a useful polar-
ity probe for micro-environments containing hydrogen bonding
groups. The high quantum yield in DMSO, DMF and alcohols qual-
ifies coumarinphenylsemicarbazone as a laser dye in the given
medium, with kF higher than knr. Contrary to previous reports that
many H-aggregates are non-fluorescent in nature, the fluorescent
H-dimer aggregates’ formation of 7-(dimethylamino)coumarin-3-
General procedure. A solution of phenylsemicarbazide (0.46 mmol)
in hot absolute EtOH (3 mL) was added to a solution of carbalde-
hyde (0.46 mmol; 100 mg) in hot absolute ethanol (5 mL). The
reaction mixture was refluxed for 15 min and the desired product
precipitated. The precipitate was filtered off and washed with cold
ethanol, dried and recrystallized from ethanol, with crystalline so-
lid products obtained in 96–99% yields (Scheme S2).
(E)-1-{[(7-dimethylamino)-2-oxo-2H-chromen-3-yl]methyli-
dene}-4-phenylsemicarbazone 1: Synthesis of 1 was published by
Donovalová et al. [17].
(E)-1-{[(7-dimethylamino)-2-oxo-2H-chromen-3-yl]methyli-
dene}-4-(4-fluorophenyl)semicarbazone 2: Obtained from 4-(4-
fluorophenyl)semicarbazide (77 mg) in 98% yield (168 mg), 1H
NMR (DMSO): d 3.07 (6H, s, AN(CH3)2), 6.62 (1H, d, J = 2.4 Hz,
ArAH), 6.74 (1H, dd, J = 8.7 Hz, 2.4 Hz, ArAH), 7.12–7.18 (2H, m,
ArAH), 7.52 (1H, d, J = 9 Hz, ArAH), 7.64–7.69 (2H, m, ArAH),
7.99 (1H, s, H-4), 8.67 (1H, s, NH), 8.89 (1H, s, NH), 10.85 (1H, s,
HC@N); 13C NMR (DMSO): d 39.5, 97.1, 108.3, 110.0, 113.3, 114.7,
115.0, 121.6, 121.7, 129.7,134.9, 138.3, 152.9, 153.1, 155.7, 160.6.
Anal. Calcd for C19H17FN4O3 (368.4) C, 61.95; H, 4.65; F, 5.16; N,
15.21. Found C, 61.92; H, 4.63; F, ndt; N, 15.19.
(E)-1-{[(7-dimethylamino)-2-oxo-2H-chromen-3-yl]methyli-
dene}-4-(4-bromophenyl)semicarbazone 3: Obtained from 4-(4-
bromophenyl)semicarbazide (111 mg) in 96% yield (191 mg), 1H
NMR (DMSO): d 3.07 (6H, s, AN(CH3)2), 6.61 (1H, d, J = 2.4 Hz,
ArAH), 6.81 (1H, dd, J = 9 Hz, 2.4 Hz, ArAH), 7.47–7.54 (3H, m,
ArAH), 7.66–7.69 (2H, m, ArAH), 7.99 (1H, s, H-4), 8.67 (1H, s,
NH), 9.03 (1H, s, NH), 10.92 (1H, s, HC@N); 13C NMR (DMSO): d
39.7, 97.1, 108.3, 110.0, 113.2, 113.9, 117.5, 121.6, 129.7, 131.1,
135.2, 138.4, 152.6, 153.2, 155.7, 160.6.
carbaldehyde in alcoholic solutions driven by p+ pꢁ interactions
–
was reported there for the first time. Furthermore, the quoted
study [17] showed that both coumarins exhibit high UF (with kF
higher than knr) also in PMMA and PVC polymer matrices.
Herein, the investigation of spectral properties of five new para-
phenyl substituted derivatives 2–6 of coumarinphenylsemicarbaz-
one 1 with various electron-withdrawing substituents in the para-
position on the phenyl ring (Scheme 1) in solution and polymer
matrix is reported. This investigation is necessary for practical
application of these new derivatives as sensors or laser dyes. The
urea/thiourea moiety plays an important role as anion binding site
in various colorimetric or fluorescent chemosensors [28–30]. Para-
substitution on the phenyl ring in the phenylsemicarbazide chain
of coumarin 1 can modify the acidity of hydrogen ions on the urea
moiety, and thus affect anion binding and receptor signal intensity.
Moreover, tuning of fluorescent properties via para-substitution
can have a positive influence on the lasing action of these dyes
and on their spectral sensitivity to the environmental conditions
such as micro-polarity and micro-viscosity. Determined spectral
properties of new phenylsemicarbazones 2–6 are compared with
those for the unsubstituted coumarinphenylsemicarbazone 1 and
the parent 7-(dimethylamino)coumarin-3-carbaldehyde.
Anal. Calcd for C19H17BrN4O3 (429.3) C, 53.16; H, 3.99; Br,
18.61; N, 13.05. Found C, 53.18; H, 4.01; Br, ndt; N, 13.07.
(E)-1-{[(7-dimethylamino)-2-oxo-2H-chromen-3-yl]methyli-
dene}-4-(4-trifluoromethylphenyl)semicarbazone 4: Obtained
from 4-(4-trifluoromethylphenyl)semicarbazide (101 mg) in 98%
yield (189 mg), 1H NMR (DMSO): d 3.07 (6H, s, AN(CH3)2), 6.61
Experimental and theoretical methods
Synthesis
General
Melting points (uncorrected) were measured on a Kofler hot
stage. 1H- and 13C NMR spectra were recorded on Varian Mercury
Plus 300 spectrometer operating at 300 MHz for 1H and 75 MHz for
13C in DMSO-d6 or CDCl3 with TMS as the internal standard. Chem-
ical shifts (d) are reported in ppm downfield of TMS and coupling
constants (J) are expressed in Hertz (Hz). All chemicals and sol-
vents were purchased from major chemical suppliers (Merck,
Darmstadt, Germany; Acros Organics, Geel, Belgium; Sigma–Al-
drich, St. Louis, MO, USA) in highest grade purity, and all solvents
were dried by standard methods and distilled prior to use. Elemen-
tal analyses were performed on a Carlo Erba Strumentacione 1106
apparatus.
7-(Dimethylamino)-2-oxo-2H-chromene-3-carbaldehyde (Mp
204–205 °C, lit. [1] 205 °C) was prepared in a 3-step reaction,
Scheme 1. Molecular structure of the studied molecules.

ˇ
M. Cigán et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
38
R
where USF is the quantum yield of standard, integrals 1 IFð
m m and
Þd
(1H, d, J = 2.1 Hz, ArAH), 6.82 (1H, dd, J = 8.7 Hz, 2.4 Hz, ArAH),
7.53 (1H, d, J = 9 Hz, ArAH), 7.65 (2H, d, J = 8.7 Hz, ArAH), 7.92
(2H, d, J = 8.4 Hz, ArAH), 8.02 (1H, s, H-4), 8.69 (1H, s, NH), 9.26
(1H, s, NH), 11.03 (1H, s, HC@N); 13C NMR (DMSO): d 39.7, 97.1,
108.3, 110.0, 113.1, 119.2, 122.4, 125.6, 125.7, 129.8, 135.6,
138.6, 142.8, 152.6, 153.2, 155.8, 160.6.
0
R1
ISFð
m
Þdm
are the areas under the emission curves, A and AS are
a0bsorbances at the excitation wavelength, and n and nS are refrac-
tive indexes of probe and standard solution, respectively. The
refractive indexes were considered only for calculation of UF in
solution. The anthracene fluorescent quantum yields in the different
media were determined by comparison with the anthracene fluo-
rescence in cyclohexane, with values of 0.22 in MeCN, 0.20 in
MeOH, 0.11 in CHCl3 and 0.16 in Tol. The quantum yields in poly-
mer matrices were 0.20 in PMMA, 0.16 in PS and 0.11 in PVC. In this
case, the fluorescence of anthracene thin polymer films and stan-
dard anthracene solution was measured in the front-face arrange-
ment. The solution and film quantum yields were corrected to
different absorptions at the excitation wavelength [33], and fluores-
cence spectra were taken from excitation at the longest wavelength
absorption-band maxima.
Anal. Calcd for C20H17F3N4O3 (418.4) C, 57.42; H, 4.10; F, 13.62;
N, 13.39. Found C, 57.40; H, 4.08; F, ndt; N, 13.38.
(E)-1-{[(7-dimethylamino)-2-oxo-2H-chromen-3-yl]methyli-
dene}-4-(4-cyanophenyl)semicarbazone 5: Obtained from 4-(4-
cyanophenyl)semicarbazide (81 mg) in 98% yield (170 mg), 1H
NMR (DMSO): d 3.07 (6H, s, AN(CH3)2), 6.61 (1H, d, J = 2.1 Hz,
ArAH), 6.81 (1H, dd, J = 8.7 Hz, 2.4 Hz, ArAH), 7.52 (1H, d,
J = 8.7 Hz, ArAH) 7.75–7.79 (2H, m, ArAH), 7.90–7.94 (2H, m,
ArAH), 8.02 (1H, s, H-4), 8.67 (1H, s, NH), 9.33 (1H, s, NH), 11.08
(1H, s, HC@N); 13C NMR (DMSO): d 39.7, 97.1, 103.8, 108.3,
110.0, 113.0, 119.2, 119.3, 129.8, 132.9, 135.9, 138.7, 143.5,
152.4, 153.2, 155.8, 160.6.
The experimental setup for detection of fluorescence lifetimes
was based on time-correlated single-photon counting (TCSPC) set-
up: analogous to that described in detail in [35] (all components
from Becker&Hickl GmbH, Berlin, Germany). The procedure is de-
scribed more simply here: the sample was excited by 375 nm pico-
second diode laser with output power ꢃ1 mW, pulse widths
typically around 50 ps and frequency rate 20 MHz. The emitted
fluorescence was spectrally separated from the laser excitation
using 395 nm dichroic filter and 397 nm long-pass filter. A pola-
rizer in magic-angle orientation was fitted in front of the detection
system to avoid distortions of decay kinetics due to depolarization
effects. The emission was measured by a 16-channel multi-anode
photomultiplier array attached to the 160 mm spectrograph
(PML-SPEC). The PML detector was run in the photon-counting re-
gime and fed the TCSPC interface card SPC-830. Fluorescence de-
cays were measured in 50 ns time-base, sampled by 1024
temporal channels. The steady-state and time-resolved fluores-
cence measurements of the coumarinphenylsemicarbazone solu-
tions were performed at 1 ꢂ 10ꢁ5 mol Lꢁ1 solute concentrations;
except for measurements in Tol, where 3 ꢂ 10ꢁ6 mol Lꢁ1 concen-
tration was applied due to limited solubility of some coumarinphe-
nylsemicarbazones in this solvent.
Anal. Calcd for C20H17N5O3 (375.4) C, 63.99; H, 4.56; N, 18.66.
Found C, 63.97; H, 4.54; N, 18.63.
(E)-1-{[(7-dimethylamino)-2-oxo-2H-chromen-3-yl]methyli-
dene}-4-(4-nitrophenyl)semicarbazone 6: Obtained from 4-(4-
nitrophenyl)semicarbazide (90 mg) in 97% yield (177 mg), 1H
NMR (DMSO): d 3.08 (6H, s, AN(CH3)2), 6.62 (1H, d, J = 2.4 Hz,
ArAH), 6.82 (1H, dd, J = 9 Hz, 2.4 Hz, ArAH), 7.53 (1H, d, J = 9 Hz,
ArAH) 7.98–8.04 (3H, m, ArAH), 8.21–8.24 (2H, m, ArAH), 8.69
(1H, s, NH), 9.53 (1H, s, NH), 11.16 (1H, s, HC@N); 13C-NMR
(DMSO): d 39.8, 97.2, 108.4, 110.1, 113.1, 118.9, 124.8, 130.0,
136.3, 138.9, 141.5, 145.8, 152.4, 153.4, 155.9, 160.7.
Anal. Calcd for C19H17N5O5 (394.4) C, 57.72; H, 4.33; N, 17.71.
Found C, 57.73; H, 4.35; N, 17.74.
Spectroscopic measurements
Anthracene (zonnally refined 99+ %, Sigma–Aldrich, Germany)
was used as the fluorescent standard. The methanol (MeOH), chlo-
roform (CHCl3), toluene (Tol) and acetonitrile (MeCN) were all UV
spectroscopy grade (Scharlau Chemie s.a., Spain).
The steady state and time-resolved fluorescence measurements
were performed in aerated solutions. All measurements on poly-
mer films were performed in the air.
Polymer films doped with coumarins were prepared by cast-
ing from solution. Films of polystyrene (PS) (Chemische Werke
Huels, F.R.G.) and poly(methyl methacrylate) (PMMA) (Diacon,
ICI, England) were prepared by casting 1 ml chloroform solution
of polymer (5 g/100 mL) containing the appropriate amount of
probe onto a 28 ꢂ 35 mm glass plate. The solvent was evapo-
rated slowly. Films of poly(vinylchloride) (PVC) (Neralit, Spolana
Neratovice s.e., CR) were prepared by similar casting from tetra-
hydrofuran solution. All three polymers were additive free.
Remaining solvents were not additionally removed from the
polymer.
UV–VIS absorption spectra were recorded by UV 1650PC (Shi-
madzu, Japan), and fluorescence spectra with a RF-5301PC spectro-
fluorophotometer (Shimadzu, Japan). The Origin 6.1 (Microcal) was
used for data plotting. Solution fluorescence was measured in a
1 cm cuvette in right-angle arrangement and quantum yields were
determined relative to anthracene in solution. Polymer film fluo-
rescence was taken in front-face arrangement on the solid sample
holder.
Theoretical calculations
The relative stability of the coumarinphenylsemicarbazone 6 H-
dimers was investigated using quantum-chemical calculations.
Structural geometries were optimized at the semiempirical PM6
level. Stationary points were characterized as minima by computa-
tions of harmonic vibration frequencies at the same theoretical le-
vel as the geometric optimization. Single point energies were
calculated at the M062X/6-311++G(d,p) level. All calculations were
performed by the Gaussian 09 program package [36].
Results and discussions
The fluorescent quantum yield (UF) of (7-dimethylamino)cou-
marin N-phenylsemicarbazones was determined in solution and
in polymer films according to Eq. (1) [33], using anthracene as
the standard in the given medium: with a quantum yield of anthra-
cene in cyclohexane of 0.25 [34].
Spectral properties
Absorption and emission spectral characteristics of the studied
coumarinphenysemicarbazones 1–6, such as the absorption (kA)
and fluorescence (kF) maxima, the molar extinction coefficients
!
R
1 IFð
m
m
Þd
m
m
AS
A
n2
ðnSÞ
(e
), the Stokes shift (mA
and the fluorescence lifetime (
matrices are presented in Tables 1–3.
–m
F), the fluorescent quantum yield (UF
)
0
UF
¼
UFS
;
ð1Þ
R
s), in various solvents and polymer
1 ISFð
Þd
2
0

ˇ
M. Cigán et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
39
Table 1
Spectral data of the studied 3-(7-dimethylamino)coumarin N-phenylsemicarbazones 1–6 in Tol at concentration 3 ꢂ 10ꢁ6 mol Lꢁ1 and in CHCl3 at concentration 1 ꢂ 10ꢁ5 mol Lꢁ1
.
b
c
d
f
Compda (R)
kA (log
e)
(nm)
kF (nm)
D
me (cmꢁ1
)
UF
Mean lifetime
s
(ns)g
ꢁ
v2h
Results of bi-exponential fitting
Tol
1 (H)
423 (4.57)
421 (4.17)
427 (4.41)
426 (4.24)
428 (4.66)
429 (4.23)
480, 507sh
476, 505sh
480, 510sh
481, 510sh
482, 510sh
481, 510sh
2752
2745
2586
2684
2618
2520
0.48
0.34
0.35
0.74
0.46
0.57
1.3 ꢁ (1.02)
2.3 ꢁ (1.12)
1.9 ꢁ (1.16)
1.6 ꢁ (1.14)
1.8 ꢁ (1.09)
1.9 ꢁ (1.07)
s1 = 0.5 ns (45%)
s2 = 2.1 ns (55%)
s1 = 2.1 ns (93%)
s2 = 4.6 ns (7%)
s1 = 1.4 ns (70%)
s2 = 3.1 ns (30%)
s1 = 1.4 ns (84%)
s2 = 3.2 ns (16%)
s1 = 1.5 ns (88%)
s2 = 3.6 ns (12%)
s1 = 1.7 ns (86%)
s2 = 3.4 ns (14%)
2 (F)
3 (Br)
4 (CF3)
5 (CN)
6 (NO2)
CHCl3
1 (H)
433 (4.61)
436 (4.63)
491, 525sh
478
2705
2015
0.49
0.70
2.7 ꢁ (1.13)
3.1 ꢁ (1.03)
s1 = 2.3 ns (72%)
s2 = 3.7 ns (28%)
s1 = 2.9 ns (82%)
s2 = 4.1 ns (18%)
2 (F)
3 (Br)
4 (CF3)
433 (4.60)
433 (4.64)
491
488, 525sh
2728
2603
0.67
0.62
3.3 ꢁ (1.18)
2.7 ꢁ (1.18)
–
s
s
s
s
s
s
1 = 2.3 ns (69%)
2 = 3.6 ns (31%)
1 = 2.4 ns (76%)
2 = 3.7 ns (24%)
1 = 0.4 ns (95%)
2 = 2.5 ns (5%)
5 (CN)
433 (4.70)
436 (4.77)
489
489
2644
2486
0.47
0.16
2.7 ꢁ (1.13)
0.5 ꢁ (1.06)
6 (NO2)
a
b
c
Structure of the probes according to Scheme 1.
Maximum of main longwavelength absorption band.
Log of the molar extinction coefficient.
Maximum of the fluorescence band and band-shoulder.
Stokes shift.
Quantum yield of fluorescence based on anthracene.
Mean fluorescence lifetime.
Quality of fitting.
d
e
f
g
h
Table 2
Spectral data of the studied 3-(7-dimethylamino)coumarin N-phenylsemicarbazones 1–6 in MeCN and MeOH at concentration 1 ꢂ 10ꢁ5 mol Lꢁ1
.
b
c
d
f
Compda (R)
kA (log
e)
(nm)
kF (nm)
D
me (cmꢁ1
)
UF
Mean lifetime
s
(ns)g
ꢁ
v2h
Results of bi-exponential fitting
MeCN
1 (H)
430 (4.59)
424 (4.63)
429 (4.57)
433 (4.25)
429 (4.62)
432 (4.52)
503
495
500
499
500
497
3375
3382
3310
3055
3310
3027
0.50
0.37
0.92
0.27
0.66
0.012
2.9 ꢁ (1.18)
1.8 ꢁ (1.07)
3.2 ꢁ (1.05)
2.9 ꢁ (1.22)
2.8 ꢁ (1.12)
Low intensity
s
s
s
s
s
s
s
s
s
s
1 = 2.6 ns (78%)
2 = 3.9 ns (22%)
1 = 1.5 ns (87%)
2 = 3.5 ns (13%)
1 = 2.8 ns (88%)
2 = 5.5 ns (12%)
1 = 2.6 ns (74%)
2 = 3.7 ns (26%)
1 = 2.6 ns (79%)
2 = 3.8 ns (21%)
2 (F)
3 (Br)
4 (CF3)
5 (CN)
6 (NO2)
–
MeOH
1 (H)
431 (4.48)
430 (4.59)
433 (4.17)
437 (4.48)
440 (4.57)
444 (4.42)
504
3280
3175
3678
3466
3422
3475
0.64
0.36
3.0 ꢁ (1.09)
2.5 ꢁ (1.10)
2.9 ꢁ (1.00)
2.3 ꢁ (1.16)
2.9 ꢁ (1.07)
1.5 ꢁ (1.06)
s
s
s
s
s
s
s
s
s
s
s
s
1 = 2.6 ns (67%)
2 = 3.8 ns (33%)
1 = 1.8 ns (64%)
2 = 3.6 ns (36%)
1 = 2.6 ns (79%)
2 = 4.3 ns (21%)
1 = 1.9 ns (77%)
2 = 3.6 ns (23%)
1 = 2.6 ns (88%)
2 = 5.2 ns (12%)
1 = 1.3 ns (89%)
2 = 3.2 ns (11%)
2 (F)
498
3 (Br)
4 (CF3)
5 (CN)
6 (NO2)
500, 515
500, 515
499, 518
505, 525
ꢃ1.00
0.67
0.32
0.015
a
b
c
Structure of the probes according to Scheme 1.
Maximum of main longwavelength absorption band.
Log of the molar extinction coefficient.
Maximum of the fluorescence band and band-shoulder.
Stokes shift.
Quantum yield of fluorescence based on anthracene.
Mean fluorescence lifetime.
Quality of fitting.
d
e
f
g
h

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M. Cigán et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
40
Table 3
Spectral data of the studied 3-(7-dimethylamino)coumarin N-phenylsemicarbazones 1–6 in polymer matrices at concentration 2 ꢂ 10ꢁ3 mol kgꢁ1
.
b
c
d
f
Compda (R)
kA (log
e)
(nm)
kF (nm)
D
me (cmꢁ1
)
UF
Mean lifetime
s
(ns)g
ꢁ
v2h
Results of bi-exponential fitting
PS
1 (H)
2 (F)
429 (4.42)
421 (4.30)
505
3508
5131
0.25
0.15
2.6 ꢁ (1.10)
2.7 ꢁ (1.17)
–
475sh, 510sh, 537
s1 = 2.4 ns (76%)
s2 = 4.0 ns (14%)
s1 = 3.1 ns (89%)
s2 = 5.3 ns (11%)
s1 = 2.6 ns (74%)
s2 = 4.1 ns (26%)
s1 = 3.0 ns (88%)
s2 = 4.1 ns (12%)
s1 = 2.8 ns (78%)
s2 = 3.9 ns (22%)
3 (Br)
432 (4.28)
430 (4.38)
428 (4.45)
432 (3.96)
509, 543
3502
4732
4633
0.12
0.12
0.50
0.13
3.3 ꢁ (1.06)
3.0 ꢁ (1.06)
3.2 ꢁ (1.32)
3.0 ꢁ (1.07)
4 (CF3)
5 (CN)
6 (NO2)
475sh, 510sh, 537
513
530
3871
4227
PVC
1 (H)
2 (F)
440 (4.43)
434 (4.61)
505
475sh, 555
2925
5023
ꢃ1.00
2.3 ꢁ (1.10)
3.4 ꢁ (1.14)
–
0.18
s1 = 3.2 ns (95%)
2 = 7.5 ns (5%)
s
3 (Br)
4 (CF3)
432 (4.79)
439 (4.65)
508
3463
4498
0.24
0.10
3.6 ꢁ (1.08)
3.5 ꢁ (1.07)
–
s
s
487sh, 526sh, 547
1 = 2.5 ns (74%)
2 = 4.2 ns (26%)
5 (CN)
6 (NO2)
439 (4.52)
442 (4.41)
512
517
3248
3282
0.19
0.17
4.1 ꢁ (1.07)
3.4 ꢁ (1.02)
–
s
s
1 = 3.1 ns (75%)
2 = 4.2 ns (25%)
PMMA
1 (H)
2 (F)
432 (4.35)
425 (4.44)
504
457sh, 537
3307
4907
ꢃ1.00
3.6 ꢁ (1.08)
3.2 ꢁ (1.13)
–
0.17
s1 = 3.0 ns (91%)
2 = 5.3 ns (9%)
s
3 (Br)
433 (4.26)
431 (4.50)
429 (4.48)
432 (4.15)
515, 540
515, 532sh
517
3677
3784
3968
4245
0.13
0.31
0.62
0.48
4.0 ꢁ (1.09)
3.6 ꢁ (1.19)
4.1 ꢁ (1.20)
3.2 ꢁ (1.10)
–
–
–
s
s
4 (CF3)
5 (CN)
6 (NO2)
529
1 = 3.0 ns (76%)
2 = 4.0 ns (24%)
a
b
c
Structure of the probes according to Scheme 1.
Maximum of main longwavelength absorption band.
Log of the molar extinction coefficient.
Maximum of the fluorescence band and band-shoulder.
Stokes shift.
Quantum yield of fluorescence based on anthracene.
Mean fluorescence lifetime.
Quality of fitting.
d
e
f
g
h
Absorption
kA values, particularly those for coumarins 5 and 6 which have the
strongest electron-withdrawing substituents (ACN, ANO2) in the
para-position on the phenyl ring, are shifted more batochromically
(ꢃ10–15 nm) in comparison with the unsubstituted coumarinphe-
nylsemicarbazone 1 (Table 2). This modest increase in kA for cou-
marins 5 and 6 observed in MeOH is explained by additional
stabilization of the ICT character of the LE S1 excited state of coum-
arinphenylsemicarbazones with strongest electron-withdrawing
para-substituents by the specific interactions (intermolecular
hydrogen bonding) between the coumarinphenylsemicarbazone
and corresponding solvent molecules. The LE ICT excited S1 state
The absorption spectra of the studied derivatives are quite sim-
ilar in solution (Figs. S1A–S4A and S8) and in the polymer matrices
(Figs. S5A–S7A), exhibiting one intense long-wavelength absorp-
tion band without vibrational structure at approximately 430 nm.
An exception was noted in derivative 6 spectra where a second
absorption band of half-intensity at approximately 330 nm was
also present due to the ‘‘4-nitroaniline-like’’ chromophoric system
in molecule 6’s structure.
As expected, the electron-withdrawing ability of the substituent
in the para-position on the phenyl ring had negligible effect on the
kA position in the studied fluorophores. The weak effect of para-
substituent has its origin in intramolecular charge transfer (ICT)
during excitation of molecules 1–6. Electron transition to the lo-
cally excited (LE) S1 state is accompanied by electron transfer from
a lone electron pair at the nitrogen atom of the dimethylamino
group to the coumarin pyranone moiety and exists somewhere be-
tween resonance structures I and II depicted in Scheme 2. The elec-
tron density change during excitation is localized in the area of the
coumarin skeleton and its near neighbourhood. Therefore, the far-
distant para-substituent (furthermore without the possibility of
full p-conjugation effect) does not influence the imine group elec-
tron density (partial positive charge on the imine ACH@NA car-
bon) and thus the kA value in most of the solvents.
The negligible effect of the para-substituent is also evident in
the signal shift for urea moiety -NH- protons in 1–6 1H NMR spec-
tra (Table S1). Only in the strongly polar protic MeOH solvent, the
Scheme 2. Charge redistribution in the locally excited singlet S1 states of molecules
1–6 in nonpolar and polar aprotic solvents.

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M. Cigán et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
41
nonpolar solvents) and 540 nm in both solvents and polymer
matrices (Figs. S1B–S8B). These two bands changes the ratio of
their intensities on moving from one matrix to another. In addition,
the fluorescence decay of 2–6 exhibited better fit using the bi-
exponential mathematical function (Tables 1–3), although the s1
and s2 values are quite similar. As observed in the unsubstituted
derivative 1 [27], uniform fluorescence excitation spectral shape
at these two different emission wavelengths excludes causation
by aggregate formation and indicates equilibrium between two
emissive ICT excited states. We assume that the origin of the two
emissive ICT states for coumarinphenylsemicarbazones 2–6 is con-
nected with the additional charge redistribution in the S1 state fol-
lowing excitation, and accompanied by the solvent reorganization.
This could be further influenced, for example, by equilibrium re-
lated to intramolecular hydrogen bond breaking during charge
redistribution (Scheme 4).
We recently published the existence of such intramolecular
hydrogen bonding in the skeleton of two isatinphenylsemicarbaz-
one derivatives [37,39]. Although the presence of the second iso-
mer can also be responsible for this effect, isomerization of the
imine C@N double bond was not observed for derivatives 2–6.
The Stokes shift of coumarinphenylsemicarbazone varies in the
range from 2000 to 5000 cmꢁ1, depending particularly on the ratio
of the intensities of two emissive ICT states. Since the increase in
mA–mF is associated with the change in the structure of the excited
state during its lifetime, one would expect easier reorganization in
the solution as in the polymer matrix. Surprisingly, the opposite ef-
fect was observed and the largest mA–mF value was recorded for 2 in
Scheme 3. Presumed charge redistribution in the locally excited singlet S1 state of
molecule 6 in polar protic solvent.
of coumarin 6 depicted in Scheme 3 is shifted slightly to the more
conjugated hydrazonol side with deeper ICT character due to the
hydrogen bonding stabilization (Scheme 3 – structure II), resulting
in decreased S1 excited state energy, and thus to increased kA.
We recently published the concentration and solvent polarity
influences on the hydrazide-hydrazonol tautomeric equilibrium
of 3-isatin N-phenylsemicarbazone and 3-(N-methyl)isatin N-phe-
nylsemicarbazone E isomers [37].
PS matrix (Table 3).
Compounds 2–6 exhibit high UF in some of the solvents and
qualify as laser dyes (kF higher than knr) in the given media (Tables
1 and 2). The derivative 3 fluorescent quantum yield approaches
0.92 in MeCN and 1.00 in MeOH. Para-substitution results in in-
creased UF for derivatives 4 and 6 in Tol, for derivatives 2, 3, 4 in
CHCl3, for 3 and 5 in MeCN, for 3 and 4 in MeOH, and for derivative
5 also in the PS polymer matrix (compared to unsubstituted deriv-
ative 1). Surprisingly, and in sharp contrast to unsubstituted deriv-
ative 1 behaviour, para-substitution in polymer matrices leads to
relatively rapid decrease in UF value in most para-substituted
coumarinphenylsemicarbazones (Table 3); with the only excep-
tions being high UF values for 5 and 6 in PMMA and increased
UF for 5 in the PS matrix. This unexpected decrease in UF values
in polymer matrices results from coumarinphenylsemicarbazone-
matrix Van der Waals intermolecular interactions and/or couma-
rinphenylsemicarbazone aggregate formation. The same absorp-
As expected, the absorption maxima of all derivatives are
slightly shifted to longer wavelengths with increasing solvent
polarity. The bathochromic shift of kA (positive solvatochromism)
implies that the electronic transitions corresponding to these
bands are p–p
* transitions. Although deviation of kA towards lower
energies in the less polar CHCl3 solvent is unexpected compared to
MeCN (Tables 1 and 2), halogenated solvents often exert unpre-
dictable effects on solvatochromism of molecules with ICT charac-
ter [38]. As mentioned in our previous study devoted to
unsubstituted coumarinphenylsemicarbazone 1 [27], we assign
this effect to decreased stabilization of the ground states of 1–6
by CHCl3 in comparison with other solvents of similar polarity.
Surprisingly, the kA values for para-substituted coumarinphe-
nylsemicarabzones 2–6 are slightly red shifted (ꢃ10 nm) in PVC
compared to the PMMA and PS polymer matrices (Table 3). Similar
to the situation in CHCl3, this effect can be connected with de-
creased stabilization of the ground states of 1–6 by PVC; although,
halogen bonding also cannot be excluded.
tion spectra shape, similar
e values in solutions and polymer
matrices and the same shape of the fluorescence excitation spectra
at different emission wavelength favours compound-matrix inter-
actions. However, in our previous studies on coumarin fluores-
cence, we did not observe such considerable quenching effect of
all studied polymer matrices on coumarin fluorescence intensity
[14,17,40,41]. To the contrary, in most cases the rigidity of the
polymer matrix increased coumarin fluorescent quantum yield.
Therefore, we assume that the bathochromic shift of kF, the largest
Emission
Compared to kA, the expected stronger dependence of kF on sol-
vent polarity and its bathochromic shift with increasing solvent
polarity (Tables 1 and 2) accords with additional stabilization of
the highly polar LE ICT S1 state of 1–6 by solvation in polar sol-
vents, typical for 7-(dialkylamino)coumarins [9,12]. Similar to the
situation in unsubstituted coumarinphenylsemicarbazone 1, we
assume that the red shift of kF for 2–6 (in comparison to the parent
7-(dimethylamino)coumarin-3-carbaldehyde) is associated with
rapid additional charge delocalization over the CH@NNHCONHPh
moiety in the excited state, as suggested for coumarinphenylse-
micarbazone 6 in Scheme 3 – motif II [17]. The additional kF shift
in polymer matrices (Table 3) most likely caused by coumarinphe-
nylsemicarbazone aggregation in the polymer matrix (see text be-
low). In contrast to symmetrical long-wavelength absorption
bands, the fluorescence spectra of derivatives 2–6 often exhibit
two overlapping emission bands at approximately 505 (or 485 in
mA–mF and the lower UF values in the polymer matrix compared to
those in solution are from intermolecular interactions in relatively
Scheme 4. Intramolecular hydrogen bonding in the structure of the studied
coumarinphenylsemicarbazones.

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M. Cigán et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
42
of 6 in polar PMMA polymer matrix (Table 3), compared to polar
solvents, support this conclusion (PMMA has higher micro-viscos-
ity and decreases the rate of non-radiative deactivation of the S1
state by rotation suppression). TICT state formation was not ob-
served in unsubstituted derivative 1 nor in other studied para-
substituted coumarinphenylsemicarbazones, even in highly polar
solvents (MeOH, MeCN).
There is controversy in the literature concerning the exact role
that hydrogen bonding plays in the formation of the TICT states of
7-aminocoumarins in protic solvents [7,17,43–45]. Recently, Barik
et al. published a detailed study with evidence for TICT formation
of coumarin C1 only in highly polar protic solvents; and no evi-
dence was supplied for TICT in highly polar aprotic solvents [45].
Similar to the situation in the parent 7-(dimethylamino)couma-
rin-3-carbaldehyde [27], a rapid decrease in UF for 6 in both MeCN
and MeOH (Table 2) and almost equal UF values in these solvents
indicate that hydrogen bonding to the solvent is not a necessary
condition for TICT stabilization of 7-aminocoumarins in highly po-
lar solvents. Moreover, rapid UF decrease connected with the TICT
state formation already in a medium polarity region (CHCl3;
Table 1) supports this finding. As we concluded in our previous
paper, the TICT stabilization of 7-aminocoumarins most likely
depends on the specific charge redistribution in a particular
coumarin, and thus its effect varies from coumarin to coumarin.
To obtain deeper insight into the quenching process of the ex-
cited state of 6, the solvent polarity effect on UF was investigated
using the Stern–Volmer relationship (Figs. S9–S12) [46]. As seen
in Fig. S9, the stepwise addition of CHCl3 to the Tol solution of 6 re-
sults (rather surprisingly) in fluorescence enhancement up to a
CHCl3 concentration of approximately 2 mol Lꢁ1. This unusual UF
enhancement at low quencher concentration was also observed
after the addition of small amounts of MeCN or MeOH to the Tol
solution of 6. However, the fluorescent enhancement window is
narrow and the quenching process starts at lower MeCN or MeOH
concentrations than in CHCl3 addition. Addition of higher quencher
concentrations leads to expected fluorescence quenching which
complies with typical Stern–Volmer quenching (Figs. S9 and
S10). We assume the unusual fluorescence enhancement at low
quencher concentrations is connected with stabilization of the CT
character of the excited state in more polar solvents, accompanied
by an increase in molecule rigidity leading to UF value enhance-
ment. However, further increase in solvent polarity shifts the ex-
cited state equilibrium to the non-fluorescent TICT state side
resulting in rapid fluorescence quenching in higher concentrations
Scheme 5. Possible intermolecular aggregation motifs with negligible influence on
the absorption spectra, but which could affect the kF position and also significantly
support non-radiative deexcitation processes.
high coumarinphenylsemicarbazone concentrations in the poly-
mer matrices (Scheme 5) rather than from coumarinphenylsemic-
arbazone-matrix interactions. While such intermolecular
interactions (originating for example from differing solubility of
2–6 compared with that for unsubstituted derivative 1) have neg-
ligible influence on the absorption spectra, they can affect the kF
position and also significantly support the non-radiative deexcita-
tion processes. The weak fluorescence band shoulders in polymer
matrices could also result from this type of aggregation. Further
studies should determine which of these processes, or alternate
factors, play a key role in these mechanisms.
The fluorescent quantum yield of 6 decreases rapidly with
increasing solvent polarity (Tables 1 and 2). We assume the in-
creased solvent polarity most likely leads to population of the
highly conjugated non-radiative TICT [42] excited state of 6
(Scheme 6), which results in increase in the non-radiative decay
rate constant knr of the excited S1 state and thus in gradual UF de-
crease. The negative charge delocalization and the overall charge
separation depicted in Scheme 6 are supported by CT resonance
structure stabilization of the ‘‘aniline-analogous’’ end of the mole-
cule 6 skeleton induced by ꢁM mesomeric effect of the ANO2
group.
Solvation in a more polar region results in a decrease in the TICT
excited state energy compared to the LE ICT state energy and sup-
ports complete electron transfer from the nitrogen atom to the
coumarinphenylsemicarbazone residue. The rapid increase in UF
Fig. 1. Fluorescent quantum yield values (UF) for 3-(7-dimethylamino)coumarin N-
phenylsemicarbazone
6 plotted against solvent polarity factor (Df): kEX = kA;
Scheme 6. Proposed charge redistribution in the TICT excited singlet S1 state of
molecule 6.
volume fractions of CHCl3 in Tol/CHCl3 solvent mixture were 0.01, 0.02, 0.05, 0.1,
0.2, 0.5 and 0.8.

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M. Cigán et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
43
of a more polar solvent. The unusual exponential decay shape of
the UF = f( f) curve (Fig. 1) in the medium to high polarity interval
D
is most likely due to TICT state saturation in highly polar solvents.
The quenching process was further investigated using a typical
singlet quencher TEMPOL (4-hydroxy-2,2,6,6-tetramethylpiperi-
dine-N-oxyl) to confirm the unusual shape of the Stern–Volmer
plot at low concentrations of a more polar solvent. In contrast to
fluorescence quenching with polar solvents, fluorescence decrease
was clearly observed immediately after the initial addition of TEM-
POL and it followed the typical Stern–Volmer quenching behaviour
(Fig. S10B). Quenching parameters are summarized in Table S2
where bimolecular quenching rate constants (kq) for MeCN and
MeOH are more than one magnitude lower than for TEMPOL. The
kq values for MeCN and MeOH are almost equal and further sup-
port our assumption that hydrogen bonding to the solvent is not
a necessary condition for TICT stabilization of 7-aminocoumarins
in highly polar solvents.
Fig. S10A shows that the Stern–Volmer plot for fluorescence
quenching of 6 by MeOH is non-linear at high MeOH concentra-
tions, and accords better with exponential growth function. The
non-linearity in the Stern–Volmer plot for 6 at high MeOH concen-
trations is caused by the ground-state aggregate formation (static
quenching) which is discussed in the next section (Self-
Aggregation).
Scheme 7. Possible H-aggregate motif of molecule 6 in highly polar solvents.
of 6 compared to the parent carbaldehyde, we assume that the
formation of fluorescent H-dimer aggregates of 6 is driven by
dipole–dipole or donor–acceptor
ethylaminocoumarin and p-nitroaniline moieties (Schemes 7, S3
and S4), and not by the (d+)–
p–p interactions between 7-dim-
p
p(dꢁ) interactions between two
coumarin moieties as occurs in the parent carbaldehyde [27].
Hydrogen bonding interactions between the phenylsemicarbazide
chains in such a highly interactive polar solvent as MeOH are pre-
cluded. Quantum chemical calculations favour the dipole–dipole
dimer formation (Schemes
8 and 9; D a
E = 42.4 kJ molꢁ1 in
Due to the weak intermolecular hydrogen bonding ability of
both radiative ICT and non-radiative TICT states, and the steep
dependence of UF on solvent polarity, coumarinphenylsemicarbaz-
one 6 appears a useful polarity probe for micro-environments con-
taining hydrogen bonding groups; similar to the parent 7-
(dimethylamino)coumarin-3-carbaldehyde [27,47].
vacuum). However, theoretical calculations did not include the
dimer-solvent interactions. Therefore, it is difficult to depict the
concrete structure of the aggregate at this stage. Unusual H-type
aggregate formation of the highly utilized C481 coumarin fluores-
cent probe in both protic and aprotic polar organic solvents was re-
cently reported by Verma and Pal [48]. Comparison of results from
time-resolved emission spectroscopy in EtOH and ACN solutions
indicated that, while the polar protic solvent more readily supports
C481 dimer formation, the polar aprotic solvent most often leads to
the formation of higher aggregates rather than to dimers.
Fluorescence of coumarinphenylsemicarbazone 6 in highly po-
lar solvents is unusual, so care must be taken when interpreting
data from fluorescence measurements of 6 at different excitation
wavelength in polar environments. On the other side, excitation
at the aggregate absorption maximum may help to distinguish be-
tween non-interactive and highly interactive polar environments.
Self-Aggregation
The appearance of the new hypsochromically shifted fluores-
cence excitation band of 6 in MeOH and MeCN (and also for deriv-
atives 4 and 5 in a smaller range), together with apparent
concentration dependence of this band at approximately 390 nm,
indicates the unusual formation of fluorescent ground-state H-
aggregates (Fig. 2, Figs. S13 and S14).
In contrast to the parent 7-(dimethylamino)coumarin-3-carbal-
dehyde, aggregate formation was observed in both protic and apro-
tic polar solvent, although the presence of the short-wavelength
excitation band is similarly more clearly evident in MeOH
(Fig. 2). Aggregates of 6 exhibit weaker fluorescence efficiency than
the parent carbaldehyde. It is important to note here that the
unsubstituted coumarinphenylsemicarbazone 1 exhibits no ten-
dency to fluorescent aggregate formation in protic or aprotic polar
solvents [27]. Due to the weaker ICT character of the ground state
Conclusion
In this paper, the spectral properties of five new para-phenyl
substituted 3-(7-dimethylamino)coumarin N-phenylsemicarbaz-
ones 2–6 with varying electron-withdrawing substituents in the
para-position on the phenyl ring were investigated in solution
and polymer matrices.
The absorption spectra of the studied derivatives are quite sim-
ilar in both solution and polymer matrices, exhibiting one intense
long-wavelength absorption band without vibrational structure.
The electron-withdrawing ability of the substituent in the para-po-
sition on the phenyl ring has negligible effect on the kA position the
studied fluorophores.
Compared to kA, the expected stronger dependence of kF on sol-
vent polarity and its bathochromic shift with increasing solvent
polarity is consistent with additional stabilization of the highly po-
lar ICT S1 state of 2–6 by solvation in polar solvents typical for 7-
(dialkylamino)coumarins. The fluorescence spectra of derivatives
2–6 exhibit two overlapping emission bands rather than symmet-
rical long-wavelength absorption bands. Similarly to the situation
in unsubstituted derivative 1, we assume that the origin of two
emissive ICT states for coumarinphenylsemicarbazones 2–6 are
connected with additional charge redistribution in the S1 state fol-
lowing excitation, accompanied by the solvent reorganization.
Fig. 2. Excitation spectra of 3-(7-dimethylamino)coumarin N-phenylsemicarbaz-
one 6 in MeOH and MeCN. Emission wavelength was set at 497 nm.

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M. Cigán et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
44
approaches 0.92 in MeCN and 1.00 in MeOH. The para-substitution
results in increased UF for at least one of the 2–6 derivatives in
every type of investigated solvent and also in the PS polymer ma-
trix. In contrast to its effect in solutions, para-substitution in poly-
mer matrices quite surprisingly leads to relatively rapid decrease
in UF value for most para-substituted coumarinphenylsemicarbaz-
ones. We assume that this is due to intermolecular interactions in
relatively high coumarinphenylsemicarbazone concentrations in
the polymer matrix. Although these intermolecular interactions
have negligible influence on the absorption spectra, they may af-
fect the kF position and also support non-radiative de-excitation
processes.
Increased solvent polarity leads to a rapid decrease in UF for
NO2 derivative 6 due to the gradual population of the nonradiative
TICT excited state which results in increased nonradiative decay
rate constant knr of the excited state. The rapid decrease in UF for
6 in medium polarity region and almost equal UF values in both
protic and aprotic polar solvents indicate that hydrogen bonding
to the solvent is not a necessary condition for TICT stabilization
of 7-aminocoumarins. As we concluded in our previous paper,
the TICT stabilization of 7-aminocoumarins most likely depends
on the specific charge redistribution in a particular coumarin,
and thus its effect varies from coumarin to coumarin.
Scheme 8. H-dimer aggregate of 6, driven by dipole–dipole interactions between 7-
dimethylaminocoumarin and p-nitroaniline moieties: Optimized geometry found at
the PM6 level of theory (A – side view, B – top view); carbon – grey, hydrogen –
white, nitrogen – blue, oxygen – red. (For interpretation of the references to colour
in this figure legend, the reader is referred to the web version of this article.)
Due to the weak intermolecular hydrogen bonding ability of
both radiative ICT and non-radiative TICT states, and the steep de-
crease in UF with increasing solvent polarity, coumarinphenylse-
micarbazone
6 appears a useful polarity probe for micro-
environments containing hydrogen bonding groups; similar to
the parent 7-(dimethylamino)coumarin-3-carbaldehyde.
Contrary to previous reports that many H-aggregates are
non-fluorescent in nature, coumarin 6 forms atypical fluorescent
H-aggregates in both protic and aprotic polar solvents. Based on
previous conclusionsvalid for the parent 7-(dimethylamino)couma-
rin-3-carbaldehyde and the unsubstituted coumarinphenylsemic-
arbazone 1, we assume that the formation of fluorescent H-dimer
aggregates of 6 is driven by dipole–dipole or donor–acceptor
p–p interactions between the 7-dimethylaminocoumarin and
p-nitroaniline moieties. Quantum chemical calculations favour the
dipole–dipole dimer formation.
Acknowledgment
The authors greatly appreciate the financial support provided
by the VEGA Grant Agency (Grant Nos. 2/0112/13 and 1/1126/11).
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2014.01.127.
References
[1] G. Jones II, W.R. Jackson, S. Kanoktanaporn, A.M. Halper, Opt. Commun. 33
(1980) 315–320, http://dx.doi.org/10.1016/0030-4018(80)90252-7.
[2] G. Jones II, W.R. Jackson, C. Choi, W.R. Bergmark, J. Phys. Chem. 89 (1985) 294–
300, http://dx.doi.org/10.1021/j100248a024.
[3] A. Nag, K. Bhattacharyya, Chem. Phys. Lett. 169 (1990) 12–16, http://
dx.doi.org/10.1016/0009-2614(90)85156-7.
[4] M.S.A. Abdel-Mottaleb, M.S. Antonious, M.M. Abo Ali, L.F.M. Ismail, B.A. El
Sayed, A.M.K. Aherief, Proc. Indian Acad. Sci. 104 (1992) 185–196, http://
dx.doi.org/10.1007/BF02863363.
[5] R.B. Bangar, T.S. Varandajaran, J. Phys. Chem. 98 (1994) 8903–8905, http://
dx.doi.org/10.1021/j100087a014.
[6] S. Nad, H. Pal, J. Phys. Chem. A 105 (2001) 1097–1106, http://dx.doi.org/
10.1021/jp003157m.
Scheme 9. H-dimer aggregate of 6, driven by donor–acceptor
between 7-dimethylaminocoumarin and p-nitroaniline moieties: Optimized geom-
etry found at the PM6 level of theory (A – side view, B – top view); carbon – grey,
p–p interactions
hydrogen
– white, nitrogen – blue, oxygen – red. (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of
this article.)
[7] R. Królicki, W. Jarze˛ba, M. Mostafavi, I. Lampre, J. Phys. Chem. A 106 (2002)
1708–1713, http://dx.doi.org/10.1021/jp013916g.
[8] S. Nad, M. Kumbhakar, H. Pal, J. Phys. Chem. A 107 (2003) 4808–4816, http://
dx.doi.org/10.1021/jp021543t.
Compounds 2–6 exhibit high UF in some of the solvents, and
thus qualify as laser dyes in the given medium, with kF higher than
knr For example, the fluorescent quantum yield for derivative 3

ˇ
M. Cigán et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 126 (2014) 36–45
45
ˇ
´
[9] P. Dahiya, M. Kumbhakar, T. Mukherjee, H. Pal, Chem. Phys. Lett. 414 (2005)
148–154, http://dx.doi.org/10.1016/j.cplett.2005.08.051.
[31] R. Flašík, H. Stankovicová, A. Gáplovsky, J. Donovalová, Molecules 14 (2009)
4838–4848, http://dx.doi.org/10.3390/molecules14124838.
[10] A.K. Satpati, S. Senthilkumar, M. Kumbhakar, S. Nath, D.K. Maity, H. Pal,
Photochem. Photobiol. 81 (2005) 270–278, http://dx.doi.org/10.1111/j.1751-
1097.2005.tb00184.x.
[11] U.S. Raikar, C.G. Renuka, Y.F. Nadaf, B.G. Mulimani, A.M. Karguppikar, M.K.
Soudagar, Spectrochim. Acta Part A 65 (2006) 673–677, http://dx.doi.org/
10.1016/j.saa.2005.12.028.
[32] Y. Liu, K. Cui, W. Lu, W. Luo, J. Wang, J. Huang, C. Guo, Molecules 16 (2011)
4527–4538, http://dx.doi.org/10.3390/molecules16064527.
[33] A. Kawski, A. Kubicki, B. Kuklinski, I. Gryczynski, J. Photochem. Photobiol. A:
Chem. 71 (1993) 161–167, http://dx.doi.org/10.1016/1010-6030(93)85068-J.
[34] J.B. Birks, Photophysics of Aromatic Molecules, Wiley-Interscience, London,
UK, 1970. pp. 121–127 (Chapter 4).
[12] A.S. Satpati, M. Kumbhakar, S. Nath, H. Pal, Photochem. Photobiol. 85 (2009)
119–129, http://dx.doi.org/10.1111/j.1751-1097.2008.00405.x.
[13] B.D. Wagner, Molecules 14 (2009) 210–237, http://dx.doi.org/10.3390/
molecules14010210.
[35] D. Chorvát, A. Chorvátová, Eur. Biophys. J. 36 (2006) 73–83, http://dx.doi.org/
10.1007/s00249-006-0104-4.
[36] M.J. Frisch, G.W. Trucks, H.B. Schlegel, G.E. Scuseria, M.A. Robb, J.R. Cheeseman,
G. Scalmani, V. Barone, B. Mennucci, G.A. Petersson, H. Nakatsuji, M. Caricato,
X. Li, H.P. Hratchian, A.F. Izmaylov, J.Bloino, G. Zheng, J.L. Sonnenberg, M. Hada,
M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Nakajima, Y. Honda,
O. Kitao, H. Nakai, T. Vreven, J.A. Montgomery Jr., J.E. Peralta, F. Ogliaro, M.
Bearpark, J.J. Heyd, E. Brothers, K.N. Kudin, V.N. Staroverov, R.Kobayashi, J.
Normand, K. Raghavachari, A. Rendell, J.C. Burant, S.S. Iyengar, J. Tomasi, M.
Cossi, N. Rega, N.J. Millam, M. Klene, J.E. Knox, J.B. Cross, V. Bakken, C. Adamo, J.
Jaramillo, R. Gomperts, R.E. Stratmann, O. Yazyev, A.J. Austin, R. Cammi, C.
Pomelli, J.W. Ochterski, R.L. Martin, K. Morokuma, V.G. Zakrzewski, G.A. Voth,
P. Salvador, J.J. Dannenberg, S. Dapprich, A.D. Daniels, Ö. Farkas, J.B. Foresman,
J.V. Ortiz, J. Cioslowski, D.J. Fox, Gaussian 09, revision A.1, Gaussian Inc,
Wallingford CT, 2009.
ˇ
ˇ
´
[14] P. Hrdlovic, J. Donovalová, H. Stankovicová, A. Gaplovsky, Molecules 15 (2010)
8915–8932, http://dx.doi.org/10.3390/molecules15128915.
ˇ
[15] M. Danko, E. Szabo, P. Hrdlovic, Dyes Pigments 90 (2011) 129–138, http://
dx.doi.org/10.1016/j.dyepig.2010.12.006.
[16] P. Verma, H. Pal, J. Phys. Chem. A 116 (2012) 4473–4484, http://dx.doi.org/
10.1021/jp210433f.
ˇ
ˇ
´
[17] J. Donovalová, M. Cigán, H. Stankovicová, J. Gašpar, M. Danko, A. Gaplovsky, P.
ˇ
Hrdlovic, Molecules 17 (2012) 3259–3276, http://dx.doi.org/10.3390/
molecules17033259.
ˇ
ˇ
´
[18] M. Cigán, J. Filo, H. Stankovicová, A. Gaplovsky, M. Putala, Spectrochim. Acta
Part A 89 (2012) 276–283, http://dx.doi.org/10.1016/j.saa.2012.01.010.
[19] A. Chatterjee, B. Maity, D. Seth, Phys. Chem. Chem. Phys. 15 (2013) 1894–1906,
http://dx.doi.org/10.1039/C2CP43483K.
´
ˇ
ˇ
[37] K. Jakusová, J. Donovalová, M. Gaplovsky, M. Cigán, H. Stankovicová, A.
Gaplovsky´, J. Phys. Org. Chem. 26 (2013) 805–813, http://dx.doi.org/10.1002/
poc.3164.
[20] H. Li, L. Cai, Z. Chen, Coumarin-Derived Fluorescent Chemosensors. Advances
in Chemical Sensors, Prof. Wen Wang (Ed.), ISBN: 978-953-307-792-5, In Tech,
[38] Y. Ooyama, R. Asada, S. Inoue, K. Komaguchi, I. Imae, Y. Harima, New J. Chem.
2012.
<http://www.intechopen.com/books/advances-in-chemical-sensors/
33 (2009) 2311–2316, http://dx.doi.org/10.1039/B9NJ00332K.
´
ˇ
ˇ
coumarin-derived-fluorescent-chemosensors>.
[39] K. Jakusová, M. Gáplovsky, J. Donovalová, M. Cigán, H. Stankovicová, R. Sokolík,
J. Gašpar, A. Gáplovsky´, Chem. Pap. 67 (2013) 117–126, http://dx.doi.org/
10.2478/s11696-012-0248-x.
[21] A. Prasanna de Silva, H.Q.N. Gunaratante, Th. Gunnlaugsson, A.J.M. Huxley, C.P.
Mc, C.P. Mc Coy, J.T. Rademacher, T.E. Rice, Chem. Rev. 97 (1997) 1515–1566,
http://dx.doi.org/10.1021/cr960386p.
ˇ
[40] M. Kaholek, P. Hrdlovic, J. Photochem. Photobiol. A: Chem. 108 (1997) 283–
[22] J. Wu, W. Liu, J. Ge, H. Zhang, P. Wang, Chem. Soc. Rev. 40 (2011) 3483–3495,
http://dx.doi.org/10.1039/C0CS00224K.
288, http://dx.doi.org/10.1016/S1010-6030(97)00081-6.
ˇ
[41] M. Kaholek, P. Hrdlovic, J. Bartoš, Polymer 41 (2000) 991–1001, http://
[23] S. Park, H.-J. Kim, Sens. Actuators B 161 (2012) 317–321, http://dx.doi.org/
10.1016/j.snb.2011.10.038.
[24] H. Kwon, K. Lee, H.-J. Kim, Chem. Commun. 47 (2011) 1773–1775, http://
dx.doi.org/10.1039/C0CC04092D.
[25] T.-K. Kim, D.-N. Lee, H.-J. Kim, Tetrahedron Lett. 49 (2008) 4879–4881, http://
dx.doi.org/10.1016/j.tetlet.2008.06.003.
[26] G.-J. Kim, H.-J. Kim, Tetrahedron Lett. 51 (2010) 4670–4672, http://dx.doi.org/
10.1016/j.tetlet.2010.07.003.
dx.doi.org/10.1016/S0032-3861(99)00241-4.
[42] Z.R. Grabowski, K. Rotkiewicz, Chem. Rev. 103 (2003) 3899–4031, http://
dx.doi.org/10.1021/cr940745l.
[43] T. López Arbeloa, F. López Arbeloa, M.J. Tapia, I. López Arbeloa, J. Phys. Chem.
97 (1993) 4704–4707, http://dx.doi.org/10.1021/j100120a024.
[44] R.S. Moog, D.D. Kim, J.J. Oberle, S.G. Ostrowski, J. Phys. Chem. A 108 (2004)
9294–9301, http://dx.doi.org/10.1021/jp0486088.
[45] A. Barik, M. Kumbhakar, S. Nath, H. Pal, Chem. Phys. 315 (2005) 277–285,
http://dx.doi.org/10.1016/j.chemphys.2005.04.018.
[46] B. Valeur, Molecular Fluorescence: Principles and Applications, Wiley–Verlag
CH, GmbH, 2001. pp. 77–79 (Chapter 4).
[47] A. Samanta, R.W. Fessenden, J. Phys. Chem. A 104 (2000) 8972–8975, http://
dx.doi.org/10.1021/jp0009960.
[48] P. Verma, H. Pal, J. Phys. Chem. A 117 (2013) 12409–12418, http://dx.doi.org/
10.1021/jp409405a.
ˇ
´
[27] M. Cigán, J. Donovalová, V. Szöcs, J. Gašpar, K. Jakusová, A. Gaplovsky, J. Phys.
Chem. A 117 (2013) 4870–4883, http://dx.doi.org/10.1021/jp402627a.
[28] J. Shao, Dyes Pigments 87 (2010) 272–276, http://dx.doi.org/10.1016/
j.dyepig.2010.04.007.
[29] K. Ghosh, S. Adhikari, Tetrahedron Lett. 47 (2006) 8165–8169, http://
dx.doi.org/10.1016/j.tetlet.2006.09.035.
[30] M. Boiocchi, L. Del Boca, D.E. Gómez, L. Fabbrizzi, M. Licchelli, E. Monzani, J.
Am. Chem. Soc. 126 (2004) 16507–16514, http://dx.doi.org/10.1021/
ja045936c.