Photoinduced intramolecular charge transfer phenomena in 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid

Article abstract of DOI:10.1016/j.saa.2010.11.010

A donor acceptor substituted aromatic system 5-(4-dimethylamino-phenyl)- penta-2,4-dienoic acid (DMAPPDA) has been synthesized and its spectral properties have been explored on the basis of steady state absorption and fluorescence spectroscopy. Spectral f

Full text of DOI:10.1016/j.saa.2010.11.010

Spectrochimica Acta Part A 78 (2011) 463–468
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Photoinduced intramolecular charge transfer phenomena in
5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid
Sankar Jana, Shalini Ghosh, Sasanka Dalapati, Samiran Kar, Nikhil Guchhait∗
Department of Chemistry, University of Calcutta, 92, A.P.C. Road, Kolkata 700009, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 17 June 2010
Received in revised form 20 October 2010
Accepted 15 November 2010
A donor acceptor substituted aromatic system 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic acid
(DMAPPDA) has been synthesized and its spectral properties have been explored on the basis of steady
state absorption and fluorescence spectroscopy. Spectral features point largely towards a possible occur-
rence of photoinduced intramolecular charge transfer process from the donor NMe2 group to the acceptor
acid group. Solvent dependency of the large Stokes’ shifted emission band and the calculated large excited
state dipole moment support the polar character of the charge transfer excited state. Quantum yield cal-
culations and effect of addition of acid and base on the steady state spectra were also performed to further
scrutinize the excited state CT character.
Keywords:
Charge transfer
5-(4-Dimethylamino-phenyl)-penta-
2,4-dienoic acid
Fluorescence
© 2010 Elsevier B.V. All rights reserved.
Stokes shift
Quantum yield
1. Introduction
is the most acceptable one for explaining dual emission from
DMABN and its analogous molecules [10,11]. In the concept of
Photoinduced intramolecular charge transfer processes and
consequent dual fluorescence in molecules bearing an acceptor and
a donor group are important in various applications in basic and
applied science. These molecules are useful as pH and ion detec-
tors, sensors for free volume measurement in polymers, probes
for the study of micro-heterogeneous environments [1,2], degree
of water penetration into the surfactant aggregates and sensing
the local polarity of the microenvironment at binding sites on
proteins and so on. The need and interest for these molecules
multiplies when it becomes clear that the photo-induced intra-
molecular charge transfer (ICT) process does play a crucial role in
biological light harvesting processes such as photosynthesis [3].
The first observation of dual fluorescence from dimethyl amino
benzonitrile (DMABN) was reported by Lippert et al. [4]. Various
models have been proposed so far to explain the dual fluores-
cence of DMABN for similar molecules with donor acceptor moiety
attached to the chromophore group. The twisted intra-molecular
charge transfer (TICT) model [5–7], the planarized intra-molecular
charge transfer (PICT) model [8], the rehybridized intra-molecular
charge transfer (RICT) model [9] and the wagging intra-molecular
charge transfer (WICT) model are some of the most discussed
among them. Till date, it is found that, out of all the proposed
models the twisted intramolecular charge transfer (TICT) model
TICT, it is proposed that in the twisted conformation the donor-
NMe2 group of DMABN is twisted 90◦ out of plane and hence is
completely decoupled from the acceptor nitrile group [5–7]. Only
when the molecule attains this conformation, complete excited
state charge transfer takes place. The lower energy band is then
thought to arise from this charge transfer (CT) state. The higher
energy emission is explained to arise from a locally excited (LE)
state.
In recent times, we have reported photophysics of a series of
systems with varying donor and acceptor groups attached to the
chromophoric benzene [12–14] and naphthalene [15,16] rings. The
donor strength was varied by choosing primary, secondary and
tertiary amino groups as charge donors. Different acceptor moi-
eties such as nitrile [17], acid [12], aldehyde, ester [13,14], etc.
were chosen. In some of the systems extra flexibility was intro-
duced in the molecules by introducing double bonds between the
chromophore ring and acceptor group. An extra flexibility intro-
duced by the way of double bond between the acceptor and the
chromophore ring has been reported by us to produce ICT even in
secondary amine donor bearing systems devoid of any ortho sub-
stitution relative to the donor [12]. In the present work, we have
synthesized a donor–chromophore–acceptor molecule DMAPPDA
and investigated its excited state ICT process using steady state
spectroscopy. Here the presence of the two unsaturated double
bonds on the acceptor side provides an extra degree of flexibility
to the molecule and also increases the distance between the donor
and acceptor groups.
∗
Corresponding author. Tel.: +91 33 23508386; fax: +91 33 23519755.
E-mail address: nguchhait@yahoo.com (N. Guchhait).
1386-1425/$ – see front matter © 2010 Elsevier B.V. All rights reserved.
doi:10.1016/j.saa.2010.11.010

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S. Jana et al. / Spectrochimica Acta Part A 78 (2011) 463–468
0.12
2. Experimental details
2.1. Materials
MCH
DOX
CHCl3
MeOH
ACN
iPrOH
H2O
0.09
The
was purchased from Aldrich Chemicals, USA and used
as received. 4-N,N-dimethylaminocinnamaldehyde and
molecule
4-N,N-dimethylaminocinnamaldehyde
0.06
0.03
0.00
methyl(triphenylphosphanylidene)acetate in dry dichloromethane
(DCM) were stirred at room temperature for 36 h. After the solvent
was removed over vacuum, the crude product was purified by silica
gel column chromatography. Then methyl ester was hydrolysed by
aq. LiOH solution in ethanol solvent and the solvent was removed
by vacuum and was acidified with acetic acid and was filtered.
The crude product was purified by repeated crystallization from
methanol to give pure acid compound (DMAPPDA) with m.p.
248 ◦C. 1H NMR (300 MHz, CDCl3) ␦ 3.01 (s, 6H, NMe2), 5.92 (s, 1H),
6.6 (d, J = 9.0 Hz, 2H), 6.74 (d, J = 10.5 Hz, 1H), 6.83 (d, J = 11.1 Hz,
1H), 7.37 (d, J = 9.0 Hz, 2H), 7.49 (d, J = 11.1 Hz, 1H). ␯IR (cm−1), 526,
699, 809, 943, 1005, 1143, 1191, 1264, 1309, 1363, 1414, 1525,
1588, 1673, 1885, 1941, 2643, 2814, 2901, 3486.
Spectroscopic grade of all solvents such as cyclohexane
(CY), methylcyclohexane (MCH), n-heptane (n-hept), n-hexane
(n-hex), tetrahydrofuran (THF), 1,4-dioxane (DOX), chloroform
(CHCl3), carbontetrachloride (CCl4), 1,2-dichloromethane (DCM),
N,N-dimethylformamide (DMF), methanol (MeOH), isopropanol
(iPrOH), butanol (BuOH), and acetonitrile (ACN) were purchased
from Spectrochem and were used after proper distillation. Ethanol
(EtOH), triethylamine (TEA), sulphuric acid (H2SO4) and phosphoric
acid (H3PO4) from E.Merck were used as received. Triple distilled
water was used for the preparation of all aqueous solutions. All
the spectral measurements were done at ∼10−5 to 10−6 M concen-
tration of solute in order to avoid aggregation and self quenching.
Gaussian 03 software [18] was used to optimize the DMAPPDA
molecule and to calculate ground state dipole (ꢀ) moment and
Onsagar cavity radius.
300
350
400
450
Wavelength(nm)
Fig. 1. Absorption spectra of DMAPPDA in different solvents at room temperature.
systems [14,17,19], the absorption maxima of DMAPPDA is found
to be red shifted due to resonance stabilization by the presence
of tertiary amine donor group, two conjugated double bonds and
acceptor acid group. The absorption band maxima position is nearly
the same in non-polar and polar aprotic solvents, but slightly blue-
shifted in protic solvents due to of the presence of intermolecular
hydrogen bonded interaction in the ground state [20,21]. Com-
paratively large blue shift in water might be due to the presence
of possible zwitterions of DMAPPDA as well as the possibility of
stronger hydrated cluster formation in water.
3.2. Emission spectra
The fluorescence spectra of DMAPPDA recorded by excitation
at respective absorption maxima in various solvents are shown
in Fig. 2a and the spectral data are presented in Table 1. In non-
polar alkane type of solvents the emission spectra are basically a
broad structured band comprising of band heads at ∼420 nm and
∼438 nm. It is seen that the emission band maximum is found to
be red-shifted with increasing solvent polarity. In polar solvents
like water and methanol the emission spectra show two bands.
Comparing with our previous studied similar systems, here too the
high energy band at ∼425 nm is assigned to emission from the LE
state and lower energy band at ∼520 nm to the CT state [22–24].
It is noteworthy to mention here that the higher energy LE band
in polar solvents corresponds very well with the position of the
2.2. Steady state spectral measurements
All absorption and emission spectra of DMAPPDA were recorded
on Hitachi UV/Vis U-3501 spectrophotometer and Perkin-Elmer
LS50B fluorimeter, respectively.
The fluorescence quantum yields of the CT species of DMAP-
PDA in solvents of different polarity were measured relative to
quinine sulphate in 0.1M H2SO4 (˚f = 0.57) as secondary standard
and calculated on the basis of following equation:
ꢀ
n20A0 If(ꢂf)dꢂf
ꢁf = ꢁ0
(1)
Table 1
ꢀ
f
n2A I0(ꢂf)dꢂf
Spectroscopic parameters measured by absorption and emission spectra of 5-(4-
dimethylamino-phenyl)-penta-2,4-dienoic acid (DMAPPDA) in different solvents at
room temperature.
f
where n0 and n are the refractive indices of the solvents, A0 and A
are the absorbance, If0 and If are the fluorescence intensity, ꢁ0 and
a
Stokes shift ꢃꢄ (cm−1
)
␸
× 103
f
Solvent
ꢂabs (nm)
ꢂflu (nm)
ꢁf are the quantum yields, and the integrals denote the area of the
fluorescence band for the standard and the sample, respectively.
n-hept
CY
MCH
n-hex
CCl4
DCM
THF
DMF
DOX
CHCl3
ACN
BuOH
iPrOH
MeOH
EtOH
H2O
377
378
379
374
383
393
380
384
380
389
377
380
368
384
377
345
420, 437
422,436
422,439
421,438
461
3640
3520
3605
3905
4415
5800
5655
6435
4950
5585
7180
6275
7055
6995
7145
9790
2.9
–
–
5.7
2.5
4.2
2.8
8.7
2.1
3.1
3.6
2.5
2.1
2.4
2.5
3.3
3. Results and discussion
509
484
510
468
497
517
499
497
3.1. Absorption spectra
The absorption spectra of the title compound DMAPPDA in dif-
ferent solvents of varying polarities and hydrogen-bonding abilities
are shown in Fig. 1 and the corresponding band maxima are pre-
sented in Table 1. As seen in Fig. 1, the absorption spectra of
DMAPPDA show a band at ∼380 nm and this band has been assigned
to S0→S1 transition of benzene chromophore due to high molar
extinction coefficient. Compare to pure benzene chromophore and
our earlier reported single double bonded donor–aromatic–aceptor
525
516
425,521
a
Error is about 10%.

S. Jana et al. / Spectrochimica Acta Part A 78 (2011) 463–468
465
a
a
1.2
1.0
0.8
0.6
0.4
0.2
0.0
ACN
ACN
DMF
7000
H2O
Dox
6000
MeOH
CHCl3
THF
CHCl3
THF
5000
n-hex
CCl4
n-hex
0.1
4000
0.2
0.3
0.4
f
b
10000
8000
6000
4000
H2O
400
450
500
550
600
Wavelength(nm)
ACN
DMF
MeOH
max
b
n-hex(
DOX(
=438nm)
em
max
CHCl3
=468nm)
BuOH
40
30
20
10
0
em
max
=497nm)
THF
CHCl (
3
em
max
CCl4
n-hex
THF(
MeOH(
ACN(
H2O(
=484nm)
max
=525nm)
em
em
max
=517nm)
em
max
=521nm)
30
40
50
60
em
max
H2O(
=425nm)
em
ET(30)
Fig. 3. Plot of (a) Stokes’ shift (ꢃꢄ) against solvent parameter (ꢃf), (b) Stokes’ shift
(ꢃꢄ) against Reichardt solvent polarity parameter ET(30).
in nature. Except water, in all other solvents, the excitation spectra
(Fig. 2b) monitored at both the high and low wavelength emission
bands match well with the corresponding absorption spectrum.
That the emissive species has high dipolar character can be
rationalized by the Solvatochromic shift of the CT band and the
change in the dipole moment of DMPPDA from the ground to the
excited state. The CT band is found to be more red-shifted with
increasing polarity of the solvent. The solvent dipoles orient them-
selves around the fluorophore to attain an energetically favorable
arrangement thereby stabilize the polar CT state. We have calcu-
lated the excited state dipole moment of the fluorophore from the
slope of the usual Lippert–Mataga plot (Fig. 3a), i.e. Stokes shift (ꢃꢄ)
vs. solvent parameter ꢃf (ε,n). Following is the Lippert–Mataga
relation [25].
300
350
400
450
500
Wavelength(nm)
Fig. 2. (a) Fluorescence emission spectra of DMAPPDA in different solvents at room
temperature. (b) Excitation spectra of DMAPPDA in different solvents monitored at
corresponding emission maxima.
LE band in alkanes. The nature of the broad emission in alkanes is
suggestive of a probable overlap of the LE state with the closely
spaced low lying CT state. Therefore, the slightly red shifted low
energy emission band in all probability may arise from the CT state
and the one at the lower wavelength from the LE state. The extra
flexibility in DAMAPPDA molecule could be the reason behind this
ICT process being strong enough to produce dual emission in alka-
nes. The CT band in water is however more blue shifted compared
to MeOH. This might be due to the formation of possible inter-
molecular hydrogen bonded clusters. The excitation spectrum of
DMAPPDA (Fig. 2b) in water monitored at emission wavelength of
∼521 nm band corresponds well with the absorption spectrum. But
when the excitation spectrum (Fig. 2b) is recorded by monitoring
at emission wavelength of 425 nm then the new excitation band is
generated at ∼398 nm which is similar to the absorption band of the
protonated species of DMAPPDA as seen while studying the effect of
acid in water. This is an indication that besides the hydrated clusters
the zwitterionic form of DMAPPDA might also be present in water.
The zwitterion will not have the free lone pair on the nitrogen atom
and thus will not produce any CT emission, but generate only the
local emission which should be very close to the LE of the hydrated
clusters. This may be the cause why the LE band in water is broad
(ꢀ∗ − ꢀ)2
ꢄ¯a − ꢄ¯f
=
× ꢃf (ε, n)
3
2ꢅε0hc
ε − 1
n2 − 1
ꢆf (ε, n) =
−
2n2 + 1
2ε + 1
where ꢄ¯a and ꢄ¯f correspond to the absorption and emission fre-
quency, respectively, in a solvent with dielectric constant ε and n is
the refractive index of the medium. The terms h, ε0, c, in the given
equation are Planck’s constant (6.626 × 10−34 JS), permittivity of
vacuum (8.85 × 10−34 VC−1 m−1), velocity of light (3 × 108 ms−1
)
and Onsagar cavity radius, respectively. The terms ꢀ* and ꢀ are the
ground and excited state dipole moments, respectively. The plot of
ꢃꢄ vs. ꢃf shows linearity for non-polar and polar aprotic solvents.
This linearity is again a proof of the polar nature of the emissive
˚
state. The value of was calculated to be 4.8 A at DFT level for the
global minimum structure of the title molecule (Scheme 1) using
B3LYP functional and 6-31G(d,p) basis set. From the ratio of the
slope of Lippert plot and calculated values of and ꢀ, the excited

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S. Jana et al. / Spectrochimica Acta Part A 78 (2011) 463–468
nitrogen to the acceptor group [12,14,15,17,19,23,24,27,33]. Addi-
tion of dilute H2SO4 to a methanolic solution of DMAPPDA produces
a new blue shifted absorption band at ∼300 nm with concomitant
decrease in intensity of the absorption band at ∼380 nm (Fig. 5a).
The new band at ∼300 nm could be generated from the proto-
nated species of DMAPPDA, which would be the ␲ → ␲* transition
of the benzene moiety having two conjugated double bonds to
the acceptor side. In case of the emission spectra, gradual addi-
tion of acid results in generation of a blue-shifted emission band
with progressive increase in intensity and decrease in intensity of
the CT band (Fig. 5b). A clear iso-emissive point is also observed
at ∼458 nm. The band at ∼420 nm is thus assigned to the proto-
nated species of DMAPPDA. In the protonated species, the H+ ion
should prefer to bind to the lone pair of nitrogen, which is then
no longer available for charge transfer process. This is why the
CT fluorescence is quenched with addition of acid. However, the
presence of the CT band with low intensity even in high concen-
tration of acid may be due to the occurrence of possible excited
state deprotonation and then usual CT process in the excited state
surface. These observations also indicate that the CT emission is
a n → ␲* type of transition. When trifluoroacetic acid was added
to the acetonitrile solution of DMAPPDA, similar absorption and
emission spectral change were observed suggesting similar proto-
nated species formation and a n → ␲* nature of the CT state. Similar
behavior was also observed when absorption (Fig. 5c) and emis-
sion spectra (Fig. 5d) were recorded by using H3PO4–NaOH mixture
at different pH solution. To determine the pKa of DMAPPDA, we
measured the absorbance values of the probe at the band maxima
in different pH solutions having same amounts of DMAPPDA. The
absorbance values were plotted against their corresponding pH and
the resulting plot shows sharp changes of absorbance at low and
high pH which reveals pKa’s of DMAPPDA to be 4.52 and 8.71 for
the ground state [34]. Similar method has been applied for emission
spectra and excited state pKa’s are 5.10 and 9.15.
Scheme 1. Optimized structure of 5-(4-dimethylamino-phenyl)-penta-2,4-dienoic
acid. (DMAPPDA) using DFT method with B3LYP hybrid functional and 6-31G(d,p)
basis set
state dipole moment was calculated to be 17.69 D. This large differ-
ence in the dipole moment from ground state (ꢀ = 7.6 D) to excited
state (ꢀ* = 17.69 D) could only be due to charge redistribution in the
excited state by the process of charge transfer from the electron rich
tertiary amino donor moiety to the acid acceptor moiety on photo
excitation. In case of the protic solvents, however, a deviation from
linearity is found in the Lippert–Mataga plot. This indicates that the
hydrogen-bonded solvents have a different type of influence on the
nature of the charge transfer state and hence also the position of
the CT band [10,17,19,26–30].
As seen in Fig. 3b, the plot of Stokes’ shift vs. solvent polarity
parameter ET(30) [31] shows two separate sets of straight lines,
one for the non-polar and the polar aprotic solvents and the other
for the polar protic solvents, indicating that the type of interactions
present in these two classes of solvents are different in nature. In the
aprotic solvents only dipolar interactions are important whereas in
the protic solvents hydrogen-bonding interactions play crucial role.
The emission spectra of DMAPPDA in the binary solvent mixture
of n-heptane and ethanol are given in Fig. 4. Addition of ethanol to
n-heptane solution of DMAPPDA shows a red shift of the emission
maximum from ∼420 nm to ∼500 nm with increase in intensity.
This observation indicates that the CT state producing the red
shifted emission band originates from the LE state [32]. The fluo-
rescence intensity of the CT band in ethanol increases due to higher
fluorescence quantum yield of the CT band in ethanol solvent than
in n-heptane solvent (Table 1).
3.4. Effect of base on steady state spectra of DMAPPDA
Addition of dilute NaOH to the water solution of DMAPPDA
shows a progressive increase of intensity of the band at ∼345 nm
(Fig. 6a). Progressive growth of the CT band with simultaneous
quenching of the high energy emission band (Fig. 6b) was observed
in the emission spectra. Similar behavior was observed at high pH
values using the H3PO4–NaOH mixtures as seen in Fig. 5c and d.
This increase in intensity of the CT band is due to decrease in con-
centration of zwitterionic species. Addition of base removes the H+
ion attached to the nitrogen atom of the zwitter ionic species and
then the system is capable of charge transfer reaction [16].
Addition of trimethylamine to an acetonitrile solution of DMAP-
PDA produces a blue shifted absorption band at 350 nm with
an isosbestic point at 367 nm (Fig. 7a). This type of shift may
be due to formation of anion of DMAPPDA or some complex of
DMAPPDA with the electron donating weak base trimethylamine.
Complexation process is clear from the emission spectra when
trimethylamine is added to the acetonitrile solution of DMAPPDA.
As seen in Fig. 7b, the emission band is again shifted to blue from
515 nm (emission band maxima of DMAPPDA in acetonitrile sol-
vent) to 498 nm with gradual decrease in intensity of the CT band
and passing through an isoemissive point at 482 nm. This also pro-
duces a high-energy band at 420 nm, which may be due to the local
emission of the complex of DMAPPDA with the electron donor weak
base trimethylamine.
3.3. Effect of acid on steady state spectra of DMAPPDA
Addition of acid produces noticeable changes in the absorption
and emission spectra of DMAPPDA, which supports the phe-
nomenon of photoinduced charge transfer reaction from donor
n-hept
Increasing EtOH conc.
60% EtOH
60
40
20
0
400
450
500
550
600
3.5. Fluorescence quantum yield measurement
Wavelength(nm)
The measured fluorescence quantum yields of DMAPPDA at
room temperature in different solvents are presented in Table 1.
Fig. 4. Emission spectra (ꢂex = 377 nm) of DMAPPDA in n-heptane + ethanol mixed
solvent.

S. Jana et al. / Spectrochimica Acta Part A 78 (2011) 463–468
467
a
a
without base
with base
without acid
with acid
0.08
0.06
0.04
0.02
0.00
0.45
0.30
0.15
0.00
280
320
360
400
Wavelength(nm)
320
360
400
b
Wavelength(nm)
without acid
with acid
b
without base
with base
30
20
10
0
120
90
60
30
0
400
450
500
550
600
450
500
550
600
Wavelength(nm)
Wavelength(nm)
c
0.4
0.3
0.2
0.1
0.0
Fig. 6. Effect of dilute NaOH on the (a) absorption spectra and (b) emission spectra
(ꢂex = 345 nm) of DMAPPDA in water.
1
2
0.05
a
without base
10
3
with base
0.04
9
8
4
0.03
0.02
0.01
0.00
5
7
6
270
300
330
360
390
Wavelength(nm)
d
8
600
450
300
150
0
e
300
350
400
10
5
Wavelength(nm)
d
7
c
30
b
b
Without base
With base
6
5
a
0
420 480 540 600
24
18
12
6
Wavelength(nm)
4
3
2
1
450
500
550
600
Wavelength(nm)
Fig. 5. Effect of dilute sulphuric acid on the (a) absorption spectra and (b) emission
spectra (ꢂex = 382 nm) of DMAPPDA in methanol. Effect of pH on the (c) absorption
(1→10, pH = 1.50, 2.48, 2.95, 3.45, 4.41, 4.94, 5.47, 5.90, 6.96, 10.03, respectively) and
(d) emission spectra of DMAPPDA in water using various H3PO4 and NaOH mixtures
(1→8, pH = 2.48, 4.12, 4.70, 5.47, 5.90, 6.96, 8.25, 10.91, respectively), inset: emission
spectra at low pH (a→e, pH = 1.02, 1.5, 2.01, 2.48, 2.95, respectively).
0
400
450
500
550
600
Wavelength(nm)
Fig. 7. Effect of triethylamine on the (a) absorption spectra and (b) emission spectra
(ꢂex = 377 nm) of DMAPPDA in ACN.

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S. Jana et al. / Spectrochimica Acta Part A 78 (2011) 463–468
The quantum yield values for the CT emission in polar aprotic sol-
vents are higher than in the polar protic solvent. In polar protic
solvents the measured quantum yields are very low [23,35]. This
may infer that intermolecular hydrogen bonding plays a crucial role
in the non-radiative process in protic solvents.
[4] E. Lippert, W. Luder, F. Moll, H. Nagele, H. Boos, H. Prigge, I. Siebold-
Blankenstein, Angew. Chem. 73 (1961) 695–706.
[5] Z.R. Grabowski, K. Rotkiewicz, A. Siemiarczuk, J. Lumin. 18 (1979) 420–424.
[6] J. Catalan, C. Diaz, V. Lopez, P. Perez, R.M. Claramunt, J. Phys. Chem. 100 (1996)
18392–18398.
[7] C. Rulliere, Z.R. Grabowski, J. Dobkowski, Chem. Phys. Lett. 137 (1987) 408–413.
[8] K.A. Zachariasse, Chem. Phys. Lett. 320 (2000) 8–13.
[9] A.L. Sobolewski, W. Domcke, Chem. Phys. Lett. 250 (1996) 428–436.
[10] A.B.J. Parusel, W. Rettig, W. Sudholt, J. Phys. Chem. A 106 (2002) 804–815.
[11] A.D. Gorse, M. Pesquer, J. Phys. Chem. 99 (1995) 4039–4049.
[12] A. Chakraborty, S. Kar, N. Guchhait, J. Photochem. Photobiol. A 181 (2006)
246–256.
[13] A. Chakraborty, S. Ghosh, S. Kar, D.N. Nath, N. Guchhait, J. Mol. Struct. 917 (2009)
148–157.
[14] A. Chakraborty, S. Kar, N. Guchhait, Chem. Phys. 320 (2006) 75–83.
[15] R.B. Singh, S. Mahanta, S. Kar, N. Guchhait, J. Lumin. 128 (2008)
1421–1430.
[16] S. Ghosh, A. Chakraborty, S. Kar, N. Guchhait, J. Lumin. 129 (2009) 482–491.
[17] A. Chakraborty, S. Kar, N. Guchhait, Chem. Phys. 324 (2006) 733–741.
[18] M.J. Frisch, et al., Gaussian 03, Revision B.03, Gaussian, Inc., Pittsburgh, PA, 2003.
[19] A. Chakraborty, S. Kar, D.N. Nath, N. Guchhait, J. Phys. Chem. A 110 (2006)
12089–12095.
[20] C.C. Dubroca, S.A. Lyazidi, P. Cambou, A. Peirigua, Ph. Cazeau, M. Pesquer, J.
Phys. Chem. 93 (1989) 2347–2358.
[21] Y. Kim, M. Yoon, Bull. Korean Chem. Soc. 19 (1998) 980–985.
[22] S. Mahanta, R.B. Singh, S. Kar, N. Guchhait, Chem. Phys. 354 (2008) 118–129.
[23] S. Mahanta, R.B. Singh, S. Kar, N. Guchhait, J. Photochem. Photobiol. A: Chem.
194 (2008) 318–326.
4. Conclusion
In the present work, the title molecule DMAPPDA was synthe-
sized and its photophysical behavior have been investigated using
steady state absorption and emission spectroscopy. The spectral
features indicate both local and charge transfer emission in non-
polar and polar solvents. The unusual excited state charge transfer
emission in non-polar alkane solvents is well evident from the
emission spectra. The LE state relaxes to the CT state, which gives
red shifted emission and the emission is sensitive to solvent polar-
ity, pH of the medium and also hydrogen bonding ability of the
solvent. The presence of hydrated clusters, zwitterionic species
of DMAPPDA in protic solvents has been characterized from the
absorption and emission spectra.
[24] R.B. Singh, S. Mahanta, S. Kar, N. Guchhait, Chem. Phys. 342 (2007) 33–42.
[25] N. Mataga, H. Chosrowjan, S. Taniguchi, J. Photochem. Photobiol. C: Photochem.
Rev. 6 (2005) 37–79.
Acknowledgements
[26] P.R. Bangal, S. Panja, S. Chakravorti, J. Photochem. Photobiol. A: Chem. 139
(2001) 5–16.
N.G. acknowledges CSIR, India (Project no. 01(2161)07/EMR-II)
and DST, India (Project no. SR/S1/PC/26/2008). S.J. and S.D. would
like to acknowledge UGC for Fellowship and Anuva Samanta, Bijan
kumar Paul for their help in this work.
[27] S. Sumalekshmy, K.R. Gopidas, J. Phys. Chem. B 108 (2004) 3705–3712.
[28] E. Lippert, Z. Naturforsch. A: Phys. Sci. 10 (1955) 541–545.
[29] N. Mataga, Y. Kaifu, M. Koizumi, Bull. Chem. Soc. Jpn. 28 (1955) 690–691.
[30] A. Kapturkiewicz, J. Herbich, J. Karpiku, J. Nowacki, J. Phys. Chem. A 101 (1997)
2332–2344.
References
[31] C. Reichardt, Chem. Rev. 94 (1994) 2319–2358.
[32] Z.R. Grabowski, K. Rotkiewicz, W. Rettig, Chem. Rev. 103 (2003) 3899–4032.
[33] A. Chakraborty, S. Kar, D.N. Nath, N. Guchhait, J. Chem. Sci. 119 (2007) 1–10.
[34] J. van Stam, J.E. Loforth, J. Chem. Educ. 63 (1986) 181–184.
[35] A.K. Singh, M. Darshi, S. Kanvah, J. Phys. Chem. A 104 (2000) 464–471.
[1] Y.H. Kim, D.W. Cho, M. Yoon, D. Kim, J. Phys. Chem. 100 (1996) 15670–15676.
[2] R. Hayashi, S. Tazuke, C.W. Frank, Macromolecules 20 (1987) 983–988.
[3] J.A. Bautista, R.E. Connors, B.B. Raju, R.G. Hiller, F.P. Sharples, D. Gosztola, M.R.
Wasielewski, H.A. Frank, J. Phys. Chem. B 10 (1999) 8751–8758.