Electromeric effect of substitution at 6 th position in 2-(Furan-2-yl)-3-hydroxy-4 H-chromen-4-one (FHC) on the absorption and emission spectra

Article abstract of DOI:10.1007/s12039-015-0786-1

Five 3-Hydroxychromones (3HCs), namely, 2-(furan-2-yl)-3-hydroxy-4H-chromen-4-one (FHC) and its four derivatives by substitution of -CH₃, -OH, -NO₂ and -Cl at 6^th position were synthesized from their corresponding 2′-hydro

Full text of DOI:10.1007/s12039-015-0786-1

c
J. Chem. Sci. Vol. 127, No. 3, March 2015, pp. 405–412. ꢀ Indian Academy of Sciences.
DOI 10.1007/s12039-015-0786-1
Electromeric effect of substitution at 6th position in
2-(Furan-2-yl)-3-hydroxy-4 H-chromen-4-one (FHC) on the absorption
and emission spectra
MANISHA BANSAL∗ and RANBIR KAUR
Department of Chemistry, Punjabi University, Patiala 147002, Punjab, India
e-mail: jindal_manisha@yahoo.co.in; ranbir.sandhu31@yahoo.com
MS received 29 April 2014; revised 10 July 2014; accepted 14 July 2014
Abstract. Five 3-Hydroxychromones (3HCs), namely, 2-(furan-2-yl)-3-hydroxy-4H-chromen-4-one (FHC)
and its four derivatives by substitution of -CH3, -OH, -NO2 and -Cl at 6th position were synthesized from their
corresponding 2’-hydroxyacetophenone and furan-2-carboxaldehyde. Various spectral transitions of all these
3-hydroxychromones (3-HCs) have been assigned by interpreting their absorption spectra in cyclohexane, ace-
tonitrile and methanol. It has been shown that the electromeric effects of substitution at 2nd and 6th positions
on the 2–3 double bond in ‘C’ ring are similar but the effect on the double bond of 4-carbonyl group is oppo-
site. It has been found that the substitution at 2nd position changes mainly the electron density directly at the
4-carbonyl group and substitution at 6th position changes the electron density of the ‘C’ ring, changing the
overall dipole moment of the molecule, which in turn changes the electron density at the 4-carbonyl group.
Emission spectral studies showed that the increase and decrease in dipole moment by substitution at 6th posi-
tion with electron withdrawing group like NO2 and electron donating group like -CH3 and -OH, stabilizes and
destabilizes the N∗ state in the polar solvents respectively.
Keywords. 3-Hydroxychromone (3HC); substitution effect; absorption and emission spectra; ESICT effect.
1. Introduction
of the furyl or 2-benzofuryl-3-hydroxychromones in
comparison to their 2-phenyl analogues.14
Recently, the detailed effect of substitution at the 2nd
and 7th positions in the 3-hydroxychromones (3HCs)
on the excited state proton coupled charge transfer has
been reviewed.4 Effect of various substituents at the
2nd position in the chromophore has been explained to
selectively stabilize the N∗ state and hence increasing
the population of N∗ state with respect to T∗ state.
On the other hand, the effect of substitution on the
‘A’ ring of 3HCs has not been studied up to the desired
extent. A few studies on the substitutions at 7th posi-
tion with electron donating group like (-OCH3)16 and
(-CONHR)15 on the absorption and emission spectra
of 3HF derivatives have been made but with no clear
explanation to this effect. Effect of substitution at 6th
position has not been studied yet except in one report,
that too by Klymchenko and Demchenko.17
3-Hydroxyflavones (3HFs) and their derivatives exhibit
excited state intra-molecular proton transfer (ESIPT)
reaction in such a way that emission from two excited
states is exhibited simultaneously formed from the ini-
tial reactant (N∗) and proton transfer reaction product
(T*). Therefore, 3HFs have attracted considerable inte-
rest in recent years due to their potential applications
as molecular probes based on their spectrally separated
(by about 100 nm) dual fluorescence.1–6 The absorption
and fluorescence spectra of 3HFs have become a source
of much valuable information on intermolecular inter-
actions under different environment. Demchenko and
co-workers demonstrated that the connection between
solvent parameters and the absorption and emission
spectra is essentially multi-parametric.7–14 An attempt
has been made to design efficient molecular sensors
by proper substitution in the chromophore system. For
example, substitution of 2-phenyl ring by 2-furyl or 2-
benzofuryl results in a 2–3 fold increase in the fluo-
rescence quantum yield in water and other solvents.15
Reason for this is attributed to the higher planarity
In this paper, the effect of substitution by -CH3, -
OH, -NO2 and -Cl at the 6th position of the title com-
pound has been studied on the absorption and emission
spectra. The change in absorption spectra is likely to
give information on the change in electron density in
its ground and excited states on the 4-carbonyl group
of the molecule. Since ESIPT process takes place by
transfer of proton from 3-hydroxy site to the 4-carbonyl
∗For correspondence
405

406
Manisha Bansal and Ranbir Kaur
The reaction mixture which turned deep red in colour
group of 3HC’s, thus showing the dual emission bands,
it is obvious that any change in electron density on 4- after 30 min was stirred further for 7–8 h. Thereafter, it
carbonyl group will alter the rate and extent of ESIPT was poured over ice, neutralised with dilute HCl and
process and hence the position and intensity of both the then the solid mass so obtained was crystallized from
emission bands of N∗ and T∗, will be affected.
methanol to afford orange yellow needles of chalcone.
The chalcone thus obtained was subjected to A.F.O.
(Algar Flynn Oyamada) reaction conditions in sodium
hydroxide and ethanol stirred at 10 5◦C with drop-
wise addition of 30% (w/v) H2O2 over an hour. This
mixture was further stirred for 5–6 h and the result-
ing reaction mixture on neutralization with dilute HCl,
gave a yellow mass which was crystallised twice from
appropriate solvents for different compounds.
Purity of the compounds was checked from the sharp
M.p. single spot on TLC plate and sharp peaks in the
UV-Vis spectrum. The structures have been confirmed
by their IR and 1H NMR spectra.
2. Experimental
2.1 Reagents and solvents
Acetonitrile (ACN), methanol (MeOH) and cyclohex-
ane were of spectroscopic grade and were purchased
from S.D. Fine chemicals, India and Loba Chemie.
The reagents used for the preparation of 2-furyl-3-
hydroxychromone derivatives were purchased from
Sigma Aldrich, USA.
2.2 Instrumentation
2.3a 2-(furan-2-yl)-3-hydroxy-4H-chromen-4-one:
Prepared from 2-hydroxyacetophenone and furan-2-
carboxaldehyde. Crystallized from MeOH:CHCl3(1:1,
v/v); yellow needles; yield 85%; M.p. 178◦C. 1H NMR
data, CDCl3: 8.24–8.26 (d, 1H, H-5, J0 = 7.64 Hz,
Ar), 7.69–7.72 (m, 2H, H-6, 7Ar), 7.61–7.63 (d, 1H, H-
4ꢁ, J0 = 8.24 Hz, Ar), 7.40–7.44 (t, 1H, H-5ꢁ, J0 = 7.2
Hz, Ar), 7.35–7.36 (d, 1H, H-3ꢁ, J0 = 3.2 Hz), 6.88 (s,
OH exchangeable with D2O), 6.66–6.67 (dd,1H, H-8,
J0 = 1.68 Hz, Jm = 3.4 Hz, Ar); IR (KBr, cm−1): 3258
(OH), 2920 (CH Ar), 1616 (C=O); Anal.calcd for
C13H8O4: C, 68.42; H, 3.50. Found: C, 68.21; H, 3.76,
which agrees with the reported one.18,19
Melting points of the synthesized compounds were
determined in open capillary. Microanalyses were per-
formed with a Vario Micro Cube Elementar Analyzer.
IR spectra were recorded with FTIR spectrophotometer
1
(Perkin Elmer, RZX) and H NMR on Bruker Avance
400 NMR spectrometer with TMS as an internal stan-
dard. Double beam UV-Vis spectrophotometer (UV-
1800 Shimadzu) equipped with UV-probe software,
has been employed for recording the UV-Vis spec-
tra. Fluorescence spectra were recorded on a Shimadzu
spectroflurophotometer (RF-5301PC).
2.3 Preparation, purification and characterization
of 6th substituted 2-(furan-2-yl)-3-hydroxy-4H-
chromen-4-one
2.3b 2-(furan-2-yl)-3-hydroxy-6-methyl-4H-
chromen-4-one: Prepared from 2-hydroxy-5-methyl-
For the preparation of 2-(furan-2-yl)-3-hydroxy-4H- acetophenone and furan-2-carboxaldehyde. Crystal-
chromen-4-one and its derivatives by substitution at lized from MeOH:CHCl3 (1:1, v/v); yellow needles;
the 6th position with those of -CH3, -OH, -NO2, yield 60%; M.p. 198◦C.20 1H NMR data, DMSO-
-Cl, (0.03 mole) of appropriately substituted 2’- d6: 9.54 (d, 1H, H-5, Ar), 7–8 (m, 5H, Ar), 6.68 (s,
hydroxyacetophenones were condensed with 2.88 g OH exchangeable with D2O), 2.55 (s, 3H, CH3-6);
(0.03 mole) of furan-2-carboxaldehyde in the presence IR(KBr,cm−1): 3225 (OH), 2919 (CH Ar), 1601
3.6 g (0.09 mole) of sodium hydroxide in ethanol at 10 (C=O); Anal.calcd for C14H10O4: C, 69.42; H, 4.13.
5◦C (scheme 1).
Found: C, 69.31; H, 4.26.
(i) NaOH/EtOH
( 10 5 °C )
(ii) 30% (w/v) H2O2
O
OH
O
(i) NaOH/EtOH
( 10 5 °C)
O
O
OH
H
+
O
R
CH
OH
3
R
R
(iii) dil. HCl
(ii) dil. HCl
O
O
O
2'-hydroxyacetophenone
R = H, CH3, OH, NO2, Cl
Furan-2-carboxaldehyde
Chalcone
FHC and their derivatives
Scheme 1. Synthetic scheme for the preparation of FHC and their derivatives.

Electromeric Effect on the Absorption and Emission Spectra
407
2.3c 2-(furan-2-yl)-3,6-dihydroxy-4H-chromen-4-
MeOH:CHCl3 (1:1, v/v); pale yellow needles; yield
one: Prepared from 2,5-dihydroxy-acetophenone and 71%; M.p. 167◦C.20 1H NMR data, CDCl3: 7.13–8.32
furan-2- carboxaldehyde. Crystallized from CH3CN; (m, 6H, Ar), 6.88 (s, OH exchangeable with D2O); IR
1
Brown mass; yield 12%; M.p. 202◦C. H NMR data, (KBr, cm−1): 3452 (OH), 2943 (CH Ar), 1628 (C=O).
DMSO-d6: 9.70 (s, 1H, OH-6), 9.44 (s, 1H, H-5, Ar)
7.83–7.21 (m, 5H, Ar), 6.67 (s, 1H, OH exchangeable
3. Results and Discussion
with D2O); IR (KBr, cm−1): 3324 (OH), 2923 (CH
Ar), 1620 (C=O); Anal. calcd for C13H8O5: C, 63.93;
Absorption spectra of six variously substituted 3-HCs
(figure 1) have been recorded in different solvents with
H, 3.27. Found: C, 63.72; H, 3.47.
varying polarity from non-polar (Cyclohexane) to polar
aprotic (ACN) and polar protic (MeOH).
A representative spectrum of FHC has been shown
in three solvents in figure 2.
2.3d 2-(furan-2-yl)-3-hydroxy-6-nitro-4H-chromen-
4-one: Prepared from 2-hydroxy-5-nitroacetophenone
and furan-2-carboxaldehyde. Crystallized from
By carefully examining the finer details of the spec-
EtOH:CHCl3 (1:1, v/v); yellow needles; yield 55%;
tra, it is clear that there are two sets of main bands,
M.p. 112◦C. 1H NMR data, CDCl3: 7.0–8.55 (m, 7H,
set I from 270 to 370 nm and set II around 250 nm.
In cyclohexane, set I consists of three peaks at 365,
348 and 315 nm and two shoulders around 333 and
304 nm. Set II has main peak at 248 nm and a small
peak at 254 nm. In FHC there are four oxygen atoms
which have non-bonding electrons. Among these, oxy-
Ar), 6.98 (s, OH exchangeable with D2O); IR (KBr,
cm−1): 3227 (OH), 2918 (CH Ar), 1618 (C=O), 1344
(NO2); Anal. calcd for C13H7O6 N: C, 57.14; H, 2.56;
N, 5.12. Found: C, 57.62; H, 2.88; N, 4.97.
gen belonging to furan ring show absorption band in the
higher energy UV region (>220 nm). Therefore, here,
three transitions due to the excitation of non-bonding
electron (n) to π∗ orbitals have been observed in cyclo-
hexane. It is well known that n-π∗ transitions become
weak and their absorption band shows a blue shift in
going from a non-polar to polar solvents. So here, dis-
appearance of two weak bands in polar solvent, which
appear in the form of shoulders in cyclohexane at 304
and 333 nm, shows that these are due to n-π∗ transi-
tions. By comparing the shape and position of the two
bands at 365 and 348 nm, observed in cyclohexane, with
those in ACN and MeOH, it is clear that the former
band is blue shifted and the latter is red shifted in going
from non-polar to polar solvents. It shows that 365 nm
band is due to the n-π∗ transition and 348 nm band
is due to the π-π∗ transition. The lowest energy peak
at 365 nm is assigned to the excitation of most easily
2.3e 2-(furan-2-yl)-3-hydroxy-6-chloro-4H-chromen-
4-one: Prepared from 2-hydroxy-5-chloroacetophe-
none and furan-2-carboxaldehyde. Crystallized from
4 '
3 '
5 '
B
1
8
O
2 '
9
O
O
2
1 '
7
C
A
3
6
R
O H
O H
1 0
5
4
O
O
1
2
R = H
3
4
5
6
R = C H 3
R = O H
R = N O 2
R = C l
Figure 1. Structures
of
2-aryl-3-hydroxychromone
derivatives.
Figure 2. Absorption spectra of FHC (2) in three solvents. I, II and III are in
cyclohexane, acetonitrile and methanol respectively.

408
Manisha Bansal and Ranbir Kaur
available non-bonding electrons of ‘O’ at 4-carbonyl molecule. The story with all the other four derivatives
group of the molecule. One of the two shoulders (3–6) is nearly similar to FHC.
(333 nm) should be due to the excitation of non-bonding
During electronic excitation of various derivatives
electrons of ‘O’ of 3-OH group and other shoulder of 3HC, there is excited state intramolecular charge
(304 nm) seems to be due to 1-oxygen heteroatom in transfer (ESICT), which in the case of 3HF is induced
the ‘C’ ring. The other low energy peak at 348 nm mainly by 1-oxygen heteroatom towards 4-carbonyl group.
in cyclohexane, which is red shifted by 1 nm in ACN The contribution of phenyl ring at the 2nd position to
and by 7.5 nm in MeOH should be due to the π- ESICT effect on 4-carbonyl, is little due to its non-
π∗ transition because of the excitation of the electrons planarityand non-conjugation.15,16 In FHC, furyl, which
belonging to the double bond of the 4-carbonyl group, replaces phenyl, is the major contributor as electron donor
which is highly conjugated. The next band at 315.5 in the molecule because planarity due to its small size
nm in cyclohexane, which remains at the same posi- increases conjugation in the molecule and is also richer
tion in all the solvents is due to the excitation of π- in electrons as compared to phenyl ring. This observa-
electrons of the 2–3 double bond in the ‘C’ ring as it tion has been reported earlier and is also observed here
remains isolated from the intermolecular solute-solvent in our spectral data (table 1).4,14,15,21 There is a red shift
interactions. Last band at 248.4 nm (set II) in cyclo- in all the n-π∗ and π-π∗ bands and also intensity of all
hexane, which remains at the same position in all the the bands is increased by going from 3HF to FHC. This
three solvents is because of the benzoylic moiety of the perspective of studying ESICT at the 4-carbonyl group,
Table 1. Spectral data for the absorption maxima (λmax) of the studied 3-Hydroxychromones in three solvents.
Band I
Cyclohexane
Acetonitrile
Methanol
λmax for
ε × 10−5
λmax for
ε × 10−5
λmax for
the Peaks
ε × 10−5
Sr. No. Compound the Peaks (dm3mol−1cm−1
)
the Peaks (dm3mol−1cm−1
)
(dm3mol−1cm−1
)
1
2
3
4
3HF
354.60
340.00
...........
304.20
...........
365.2
347.8
.........
315.6
.........
366.00
348.00
...........
...........
............
0.112
0.141
.......
0.102
.........
0.221
0.252
........
0.172
........
0.0638
0.0765
..........
...........
..........
............
340.0
.........
304.20
.........
............
348.8
..........
315.6
........
..........
349.20
........
..........
.........
...........
0.178
..........
0.141
........
........
0.222
........
0.141
.........
.........
0.149
.........
0.122
..........
............
...........
...........
............
344.20
.........
305.10
.........
............
355.4
..........
316.20
........
..........
356.40
...........
...........
...........
...........
..........
0.145
........
0.104
........
..........
0.196
.........
0.112
.........
.........
0.169
.........
.........
............
.............
.............
.............
FHC
6MEFHC
6OHFHC
...........
...........
338.61
................
................
Broad band
at 340–352 nm
...........
...........
..........
..........
..........
.........
358.20
..........
309.60
.........
..........
353.80
.........
325.40
..........
.............
.............
..........
0.164
.........
0.178
...........
.........
0.214
..........
0.156
.........
............
............
.............
0.107
............
0.126
.............
.........
0.251
5
6
6NO2FHC
6ClFHC
376.40
358.20
.........
301.0
........
371.00
354.20
..........
327.80
..........
0.0200
0.0240
.........
0.0280
............
0.150
0.170
.........
0.119
........
363.40
..........
310.00
.........
..........
360.40
.........
.........
..........
............
..........
..........

Electromeric Effect on the Absorption and Emission Spectra
409
which in turn affects the ESIPT, has been taken as the for NO2 substituent (6NO2FHC), while the position of
reference method for the study of ESICT effect by the this band for other 3HC derivatives remains the same
substitution at the 6th position.
in all the solvents. It seems that NO2 being a strong
However, the effect of substitution in benzoylic EWG decreases the electron density in the benzoylic
part of 3HC has not been explored except a few part of the molecule and hence the observed blue shift
reports.15–17,22 Demchenko et al. have studied the effect and decreased intensity of this band.
of OCH3 group, an electron rich chromophore, at the 7th
Among the absorption bands in set I, the n-π∗ transi-
position on both the absorption and emission spectra.16 tion due to ‘O’ of 3-OH group, which is only observed
Interestingly, the effect of this electron rich substituent using cyclohexane as the solvent, is not significantly
produces an opposite effect to that of substituents at the changed by substitutions. The effect, whatever it may
2nd position on the electron density of the 4-carbonyl be, can be better studied from the ESIPT effect in the
group.
emission spectra. The n-π∗ transition due to ‘O’ of
Here, in the studied derivatives of 3HC, substitution 4-carbonyl group at 365 nm, which also only appears
has been made at the 6th position with electron donor in cyclohexane as a solvent in all 3HCs (2-6), varies
groups (EDG) like that of CH3, OH and electron with- between 365 to 377 nm. In FHC, it is red shifted by
drawing group (EWG) like that of NO2. The effect of more than 11 nm as compared to 3HF. Among the
Cl group, which has negative inductive effect and pos- derivatives of FHC, the significant red shift, which is
itive resonance effect, has also been included. Role of more than 10 nm, is only observed by going from FHC
these substitutions at the 6th position on the electron to 6NO2FHC.
density of 4-carbonyl group has been interpreted from
Similarly, the position of the π-π∗ transitions due to
the changes brought in their absorption spectra.
4-carbonyl group varies from 340 to 360 nm in both
Broadly, there are all types of absorption bands in cyclohexane and ACN and the range in MeOH is from
the case of all 3HCs as observed in FHC as shown in 344 to 364 nm, which is slightly red shifted. There is a
figures 3 and 4. Spectrum of OH substituent significant red shift of about 8 to 10 nm in going from
(6OHFHC) could not be recorded in cyclohexane 3HF to FHC and about 10 nm by going from FHC to
because of its immiscibility in cyclohexane. For all the 6NO2 FHC in all the solvents.
other five 3HCs, the range of the band due to ben-
Range of the absorption band due to double bond
zoylic part of the molecule varies between 240 nm to (2–3 bond) in the ‘C’ ring is from 301 to 330 nm
250 nm. The significant blue shift (about 10 nm, along for all 3HCs (1 to 6) in all the solvents. There is a
with the decrease in intensity) among these 3HCs is red shift of about 10 nm by going from 3HF to FHC
Figure 3. UV/VIS absorption spectra of various substituted derivatives of
3HC in acetonitrile. I, II, III and IV are 2, 6, 5 and 3 respectively.

410
Manisha Bansal and Ranbir Kaur
Figure 4. UV/VIS absorption spectra of various substituted derivatives of
3HC in methanol. I, II, III and IV are 6, 2, 3 and 5 respectively.
molecule as has been reported.16,17 Here, the substitu-
tion at the 2nd position primarily changes the electron
density directly at the 4-carbonyl group and substitution
at the 6th position changes the electron density of the
‘C’ ring directly, which strongly increases the overall
dipole moment of the molecule, which in turn changes
the electron density at 4-carbonyl group (scheme 2).
Figures 5 and 6 show the effect of substituent on the
emission spectra. The red shift and increased IN∗/IT∗ in
FHC as compared to 3HF is on the lines of already
reported results.14,15 The only significant effect of sub-
stitution at the 6th position is on the position of the N∗
band and on the IN∗/IT∗ ratio in polar solvents. Position
of N∗ band shows a red shift of 5 nm in NO2 substituent
and a further red shift of about 12 nm by going from
FHC to 6MEFHC and 6ClFHC. In OH substitution
(6OHFHC) the shift is so high, that the two π-π∗
absorption bands, one in the ‘C’ ring (2–3 double bond)
another due to the 4-carbonyl group merge to form a
broad band between 340 to 352 nm in methanol. How-
ever, there is a blue shift of about 15 nm in cyclohex-
ane and 6 nm in ACN and MeOH in going from FHC
to 6NO2 FHC. It is an obvious result that EDG at the
6th position increases the electron density at the ‘C’ ring
which causes the red shift like that of furyl at the 2nd
position and EWG (NO2) has the opposite effect.
Although the substitution at the 6th position affects
all the absorption bands by smaller or greater extent
by changing the electron density or dipole moment
of the molecule but the effect on the electron den-
sity/dipole moment of the π-π∗ band due to the 4-
carbonyl group mainly participates in the ESIPT pro-
cess. Electron donating group (EDG) at the 6th posi-
tion makes a blue shift and electron withdrawing group
(EWG) shows a red shift in this band. Furthermore,
the gap in energy between π-π∗ transitions due to 4-
carbonyl group and at 2–3 position of ‘C’ ring remains
nearly the same in 3HF and FHC. While here, with
EDG at the 6th position this gap is decreased and
with EWG, there is a significant increase in this gap
(table 1).
O
O+
ESICT
O
H
O
O-
H
O
1
O
O+
O
O
ESICT
O
O
O
O-
H
All this data shows that the behaviour of various sub-
stituents at the 6th position is different from that of sub-
stituent at the 2nd position. The electromeric effect of
this kind of substitution on 2–3 double bond in the ‘C’
ring is similar but the effect on the double bond of
4-carbonyl group is opposite.
The effect of substitution is actually due to two
parameters, in individual or in combination, one
because of the change in electron density and second
because of the change in the overall polarity of the
H
2
O+
O
O
O
ESICT
O-
O-
N+
O
O
N+
O-
O
O
O
H
H
5
Scheme 2. Effect of substitution on ESICT.

Electromeric Effect on the Absorption and Emission Spectra
411
Table 2. Wavelength maxima of emission from N∗ and T∗
of the substituted 3-hydroxychromones in three solvents.
N∗
T∗
Solvent
Compounds
λ
λ
IN∗/IT∗
..........
max/nm
max/nm
Cyclohexane
1
2
3
4
5
6
1
2
3
4
5
.........
.........
.........
........
.........
527
534 ...........
533 ...........
.......... .............
550 ............
....... .............
527 0.0266
534 0.0695
534 0.0483
534 0.0681
535 0.4857
.........
Acetonitrile
Methanol
400**
415**
416**
417**
407(peak),
424 (shoulder)
426
Figure 5. Fluorescence spectra of various substituted
derivatives of 3HC in methanol. I, II, III and IV are for 3, 6,
2 and 5 respectively. Exciting wavelength, 359 nm.
6
1
2
3
4
5
539 0.2015
531 0.3634
530 1.4313
531 0.9809
525 0.6540
407
425
426
420
(5) and a blue shift of 5nm in OH substituent (4) in
methanol only along with significant increase (2 times)
in IN∗/IT∗ ratio in former and decrease (2 times) in the
latter case as compared to FHC (table 2).
407(shoulder), 530 2.8079
430 (peak)
6
435
540 1.1456
In the case of Cl substituent, the effect on the emis-
sion bands is more pronounced than in the absorption
spectra. There is red shift in both the N∗ and T∗ bands
along with the significant (3 times) increase in IN∗/IT∗
in ACN. ESIPT may be affected either by the change
in electron density at 4-carbonyl group or/and by the
increased dipole moment of the molecule. Klymchenko
et al. have studied the effect of charged substituents at
6th position on absorption and emission spectra as com-
pared to its neutral analogues. It has been shown that
absorption and emission spectra are shifted to longer
wavelength with respect to its neutral analogues. The
attached positively charged ammonium group also dra-
matically increases the IN∗/IT∗ ratio in all the solvents.17
Here, our results on the absorption and emission spectra
are also on the same lines. The increase and decrease in
dipole moment by substitution at the 6th position with
N∗
λ
and λT∗ are the position of the emission maxima of the
max
N∗ and T∗mfoaxrms, respectively. IN∗/IT∗ are intensity ratios of
two emission maxima.
** indicate the broad band.
EWG and EDG stabilizes and destabilizes the N∗ state
in the polar solvents respectively. The difference in the
present studies and the earlier observations is that the
substituents have increased the dipole moment of the
molecule directly but here, the change is brought about
by the ESICT effect.
4. Conclusions
Behaviour of the substitution in the benzoylic moi-
ety is different from the substitution at 2nd position
in 3HC molecules. Both these kinds of substitutions
affect the electron density at the 4-carbonyl group of
the molecule. Substitution of groups with different elec-
tromeric effect at the 6th position changes the electron
density indirectly by changing the dipole moment of the
‘C’ ring, instead of directly affecting the charge density
at 4-carbonyl group, unlike the substitution at the 2nd
position which directly changes the electron density at
4-carbonyl group.
Supplementary Information
The proton NMR /D2O data for various synthe-
sized compounds (2 to 6) have been assigned in the
figures S1–S12.
Figure 6. Fluorescence spectra of various substituted
derivatives of 3HC in acetonitrile. I, II, III and IV are for 3,
6, 2 and 5 respectively. Exciting wavelength 359 nm.

412
Manisha Bansal and Ranbir Kaur
8. Klymchenko A S, Ozturk T, Pivovarenko V G and
Acknowledgement
Demchenko A P 2001 Tetrahedron Lett. 42 7967
9. Ercelen S, Klymchenko A S and Demchenko A P 2002
Anal. Chim. Acta. 464 273
One of the authors gratefully acknowledges the Univer-
sity Grants Commission (UGC), New Delhi for award-
ing “MANF”. We are also thankful SAIF/CIL, Punjab
10. Klymchenko A S and Demchenko A P 2002 J. Am.
Chem. Soc. 124 12372
1
University, Chandigarh for providing us H NMR and
11. Demchenko A P, Ercelen S, Roshal A D and
Klymchenko A S 2002 Polish J. Chem. 76 1287
12. Klymchenko A S, Pivovarenko V G and Demchenko
A P 2003 J. Phys. Chem. A 107 4211
IR data of the synthesized 3-hydroxychromones. Our
heartiest thanks to Prof. W. R. Bansal (Retd., Chemistry
Department, Punjabi University, Patiala) who helped us
during our research work.
13. Klymchenko A S, Demchenko A P, PivovarenkoV G,
Duportail G and Mely Y 2003 J. Fluoresence 13 291
14. Klymchenko A S, Pivovarenko V G and Demchenko
A P 2003 Spectrochimi. Acta A 59 787
15. Klymchenko A S and Demchenko A P 2004 New J.
Chem. 28 687
16. Klymchenko A S, Demchenko A P, Pivovarenko V G
and Ozturk T 2003 New J. Chem. 27 1336
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