Synthesis and detailed spectroscopic characterization of various hydroxy-functionalized fluorescent chalcones: A combined experimental and theoretical study

Article abstract of DOI:10.1016/j.saa.2015.05.085

Abstract Four different bright yellow to orange hydroxy-substituted chalcones (i.e., 2′,4-di-hydroxy (1), 2′,3′,4-trihydroxy (2), 2′,3′,4′-trihydroxy (3), and 2′-hydroxy-4-methoxy (4) chalcones) were synthesized and characterized by LC-MS, FT-IR, FT-Raman

Full text of DOI:10.1016/j.saa.2015.05.085

Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 150 (2015) 557–564
Contents lists available at ScienceDirect
Spectrochimica Acta Part A: Molecular and
Biomolecular Spectroscopy
journal homepage: www.elsevier.com/locate/saa
Synthesis and detailed spectroscopic characterization of various
hydroxy-functionalized fluorescent chalcones: A combined
experimental and theoretical study
a,
M. Jagadeesh a, M. Lavanya b, B. Hari Babu c, Kiryong Hong a, Rory Ma a, Joonghan Kim d, , Tae Kyu Kim
⇑
⇑
a Department of Chemistry and Chemical Institute of Functional Materials, Pusan National University, Busan 609-735, Republic of Korea
b Department of Chemistry, Sri Venkateswara University, Tirupati 517502, Andhra Pradesh, India
c Department of Surgery, Montreal General Hospital, McGill University, Montreal, Canada
d Department of Chemistry, The Catholic University of Korea, Bucheon 420-743, Republic of Korea
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
ꢀ
ꢀ
ꢀ
Interpretations of IR and Raman
spectra of hydroxyl-substituted
chalcones.
Prepared hydroxyl-substituted
chalcones as good semiconducting
materials.
The white-light emitting property of
prepared hydroxyl-substituted
chalcones.
a r t i c l e i n f o
a b s t r a c t
Four different bright yellow to orange hydroxy-substituted chalcones (i.e., 20,4-di-hydroxy (1),
20,30,4-trihydroxy (2), 20,30,40-trihydroxy (3), and 20-hydroxy-4-methoxy (4) chalcones) were synthesized
and characterized by LC–MS, FT-IR, FT-Raman, and fluorescence spectroscopy and thermogravimetric anal-
ysis. UV–visible absorption spectroscopy was also used. The experimental (theoretical) bandgaps of 1, 2, 3,
and 4 are 2.89 (2.90), 2.93 (2.95), 3.04 (3.09), and 3.01 (2.91) eV, respectively. The hydroxy-substituted chal-
cones exhibited strong dual emissions as a consequence of the locally excited states followed by internal
charge transfer processes. The molecular structures, lowest energy transitions, vibrational frequencies,
and spectroscopic information were calculated using density functional theory and time-dependent den-
sity functional theory methods at the B3LYP/6-31G(d,p) theoretical level. The experimental and theoretical
data were compared and the relationship between them was briefly discussed.
Article history:
Received 2 January 2015
Received in revised form 16 May 2015
Accepted 20 May 2015
Available online 9 June 2015
Keywords:
Hydroxy-substituted chalcones
DFT calculations
HOMO–LUMO
Vibrational spectra
Ó 2015 Elsevier B.V. All rights reserved.
Introduction
because of their wide range of applications [1]. These bichro-
mophoric molecules, which have two chromophoric groups
Benzylideneacetophenones, which are commonly known as
chalcones, have gained significant attention in modern chemistry
separated by a hetero-vinyl chain, serve as precursors of several
heterolytic compounds like flavonoids, flavones, and pyrazolones
[2–5].
Chalcones
are
excellent models
for
studying
photo-induced electron transfer processes, which play a key role
in different fields such as polymer, photo, optic, and laser physics
[6,7]. These chromophores, which feature electron-donor and
⇑
Corresponding authors.
E-mail addresses: joonghankim@catholic.ac.kr (J. Kim), tkkim@pusan.ac.kr
(T.K. Kim).
http://dx.doi.org/10.1016/j.saa.2015.05.085
1386-1425/Ó 2015 Elsevier B.V. All rights reserved.

558
M. Jagadeesh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 150 (2015) 557–564
electron-acceptor groups connected via a
p
-conjugated spacer, are
Spectroscopic characterizations
called donor– –acceptor (D– –A) systems [8]. Chalcones are clas-
p
p
sified into symmetrical and asymmetrical donor–acceptor–donor
(D–A–D) systems based on the electron-donating substituents
attached to the aromatic rings at the end of the carbonyl functional
group: Symmetrical D–A–D chalcones contain electron donors on
both phenyl rings, while asymmetrical D–A–D chalcones have elec-
tron donors at only one of the two phenyl rings [9]. Hence, these
molecules can show highly efficient intramolecular charge trans-
fers, and thus they are particularly useful in the development of
nonlinear optical systems (NLO materials) [10]. They are also used
for ultrafast optical nonlinearities [11] and as absorption filters for
UV light [12].
Among the various chalcone derivatives, hydroxy chalcones
and related derivatives have proven to be challenging candidates
that attract wide biological interest. For example, a number of
pharmacological applications of these derivatives have been
investigated because of their antitumor [13–15], antidiabetic
[16], antimalarial [17], antioxidant [18], antifungal [19],
anti-angiogenic [20], and anti-inflammatory activities [21]. In
particular, electron-releasing groups that induce high polarization
of the ring enhance the antibacterial [22–24] and
enzyme-inhibition activity [25,26]. In addition, 20-hydroxy
chalcones like chalcone 1 and 4 are suitable for quantitative
analysis of metal ions because of their good complexing ability
[27]. The applications of chalcones also extend to agrochemicals
and artificial sweeteners [7].
FT-IR spectral measurements were recorded in the solid state
using KBr pellets on a JASCO FTIR 5300 spectrophotometer between
4000 and 400 cmꢁ1. UV–visible spectra of the synthesized com-
pounds were recorded using a JASCO V-570 UV–visible spectropho-
tometer. Mass spectra of the molecules were recorded using an
Agilent Technologies 6530 Accurate Mass Q-TOF LC/MS. Raman
spectra were measured using a confocal Raman microscope (Lab
Ram HR 800, Horiba Jobin Yvon SAS, France) equipped with a
432 nm He-Ne laser (Torus Laser, Laser Quantum, France) at a power
of 50 mW and a 50ꢂ LWD air-dry visible objective (NA = 0.5 wd 10.6
MM LIEU Microsystems of Model BX 41) that was attached to a
Fieltiyar multichannel CCD detector; two scans were recorded.
Each Raman spectrum was measured in the range of 400–
1800 cmꢁ1 at a spectral resolution of 0.35 cmꢁ1/pixel with an
1800 g/mm grating at the confocal pinhole, which was set at
400 nm. Fluorescence studies of the solid samples were recorded
using a Hitachi F-7000 fluorescence spectrophotometer at room
temperature. The chalcones were thermally analyzed using a
Labsys TG-DSC 1600 model instrument under a N2 atmosphere at
a scan rate of 10 °C/min. Scanning electron microscopy (SEM)
images of the chalcone molecules were obtained using a Carl Zeiss
EVO MA 15 Thermonic Emission scanning electron microscope.
DFT calculations
Although hydroxy-substituted chalcones have a variety of
applications, especially in pharmacological fields, detailed
elucidations of the structural and spectroscopic properties of
these hydroxy-substituted chalcones have rarely been
reported. Detailed spectroscopic assessments may aid in gener-
ating facile syntheses of new chalcone derivatives and advance
the pharmacological applications of hydroxy-substituted chal-
cones. In this work, we report the preparation and structural
elucidation of four hydroxy-substituted chalcones, i.e.,
20,4-dihydroxychalcone (1), 20,30,4-trihydroxychalcone (2), 20,3
0,40-trihydroxychalcone (3), and 20-hydroxy-4-methoxychalcone
(4) using a variety of spectroscopic methods. In addition, theo-
retical approaches including DFT and TD-DFT calculations are
used to study their molecular vibrations, frontier orbitals, and
electronic transitions. The experimental and calculation data
are compared and the relationship between them is briefly
discussed.
To determine the properties of these chalcone molecules (1–4)
at the molecular level, density functional theory (DFT) [29,30] was
employed. The geometries of the chalcone molecules were fully
optimized using Becke’s three parameter hybrid functional [31]
combined with the Lee, Yang, and Parr [32] correlation functional
(B3LYP) using the standard Pople basis set, i.e., 6-31G(d,p),
[33,34] for all atoms (i.e., H, C, N, and O atoms) in the gas phase.
To validate that these optimized structures were global minima,
the vibrational frequencies were also calculated using the same
level of theory. Moreover, time-dependent DFT (TDDFT) calcula-
tions were used to investigate the optical properties of these four
chalcone molecules. The DFT-optimized structures were employed
and the same level of theory was used for TDDFT. We also used an
integral equation formalism variant of the polarizable continuum
model (IEFPCM) [35,36] for ethanol to account for the bulk solvent
effects for all TDDFT calculations. All DFT and TDDFT calculations
were performed using the Gaussian 09 program [37].
Materials and methods
Results and discussion
Chemicals and syntheses of hydroxy chalcone derivatives
FT-IR and FT-Raman spectral investigations
All chemicals and solvents used in the present work were
obtained from commercial sources and used without any further
purification. 4-Hydroxybenzaldehyde, 20-hydroxyacetophenone, 2
0,40-dihydroxyacetophenone, benzaldehyde, 20,30,40-trihydroxyacet
o-phenone, and 4-methoxybenzaldehyde were purchased from
Sigma Aldrich. The target chalcones were prepared according to
the conventional base-catalyzed Claisen–Schmidt reaction as per
the literature [28]. Equivalent molar amounts of an ethanolic solu-
tion of the hydroxy-substituted acetophenone with the corre-
sponding benzaldehyde were mixed in a round-bottom flask.
After adding 10% NaOH solution, the mixture was stirred at room
temperature for 8–10 h. After complete consumption of the corre-
sponding aldehyde, the solution was neutralized using 10% HCl.
The precipitate was collected by filtration, dried, and recrystallized
from ethanol.
FT-IR spectroscopy can serve as an important basic tool for
characterization of organic and inorganic molecules. In this work,
experimental IR spectra of hydroxy chalcones (1–4) were com-
pared and analyzed with respect to those obtained from DFT calcu-
lations (B3LYP/6-31G(d,p) level). The DFT-optimized molecular
structures of 1–4 are shown in Fig. 1. The FT-IR and FT-Raman
spectra of the synthesized chalcone derivatives are shown in
Figs. 2 and 3, respectively. The theoretical spectra are also shown
for comparison. We assigned only the important peaks in the
FT-IR and FT-Raman spectra because there are only a limited num-
ber of references for the IR spectra of other chalcone molecules for
comparison. As shown in Figs. 2 and 3, the experimental patterns
of the IR and Raman peaks are much more complex because of
overlapping peaks and the presence of highly active vibrational
groups. The specified vibrations that occur at similar

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559
Fig. 1. Optimized structures of chalcones 1–4 from DFT calculations performed at the B3LYP/6-31G(d,p) level.
Fig. 2. FT-IR spectra of chalcones 1, 2, 3 and 4 recorded from 4000 to 400 cmꢁ1. The
experimental spectra are shown in black and theoretical spectra are shown in blue.
(For interpretation of the references to colour in this figure legend, the reader is
referred to the web version of this article.)
Fig. 3. FT-Raman spectra of the synthesized chalcones 1, 2, 3 and 4 recorded from
1800 to 400 cmꢁ1. The experimental spectra are shown in black and theoretical
spectra are shown in red. (For interpretation of the references to colour in this
figure legend, the reader is referred to the web version of this article.)
wavenumbers/range are assigned in details for each of the mole-
cules (1–4). Tables S1–S4 in the Supplementary Material clearly
show the overlapping bands occurring at specific wavenumbers;
for instance, the hydrogen bonded carbonyl group overlapped by
the aromatic C@C bond vibrations and the hydrogen bonded OH
functional group overlaps with the aromatic C–H stretching vibra-
tions. In the previous study [38], the intramolecular hydrogen
bonding in 20-hydroxy chalcones allows these molecules to exhibit
cis-to-trans isomerization which further influences the spectro-
scopic properties. The theoretical spectra deviate from the
experimental spectra, because the former was performed on a free
molecule in vacuum ignoring the molecular interactions. While,
the later was obtained for solid samples in which the molecules
are strongly involved with interactions such as hydrogen bondings.

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M. Jagadeesh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 150 (2015) 557–564
Moreover, the neglecting of anharmonicity might be a major cause
for the deviation and complexity in the vibrational frequencies. The
possibility of exhibiting conformational isomerism by these mole-
cules can also be taken as one of the main causes for bringing com-
plications in the experimental spectra [39–41].
which in turn is influenced on inductive, conjugative, field and
steric effects. The presence of 4/40-donor groups promotes the
delocalization of
p electrons via a–b unsaturation, which decreases
the C@O bond order and thus increases the bond order between
the carbonyl carbon and
a carbon atom [40,41].
Aromatic C@C vibrations
C@O vibrations
In chalcone 1, aromatic C@C bond stretching of the two phenyl
rings is observed at 1606 cmꢁ1 in the Raman spectrum and
1620 cmꢁ1 in both the DFT-IR and DFT-Raman spectra. In the
experimental IR spectrum, the corresponding peak overlaps with
the carbonyl stretching band. For chalcone 2, the band correspond-
ing to the carbonyl group dominates the aromatic C@C stretching
peak in the IR spectrum; the same peak appears with medium
intensity in the Raman (1628 cmꢁ1), DFT-IR (1626 cmꢁ1), and
DFT-Raman (1618 cmꢁ1) spectra. Compound 3 exhibits C@C vibra-
tional bands in both the experimental and theoretical spectra. The
corresponding bands are observed in the IR (Raman) experimental
and DFT spectra at 1632 (1638) and 1630 (1638) cmꢁ1, respec-
tively. In the case of 4, the presence of the strong mesomeric group
at the para position of the phenyl ring significantly influences the
carbonyl functional group. As a result, no band is observed for
the C@C bond vibration at the specified wavenumber that corre-
lates with the band observed in the theoretical spectra. In the
DFT-calculated IR and Raman spectra of chalcone 4, the bands at
1622 cmꢁ1 were assigned to the C@C vibrations.
Identification and assignment of the carbonyl group in the chal-
cones is crucial because of several factors, such as resonance, intra-
and/or intermolecular hydrogen bonding, and type of substituent
attached to the phenyl rings, affect the stretching vibrations of
the
a–b unsaturated carbonyl group. In chalcone 1, the carbonyl
group produced intense peaks at 1628 and 1634 cmꢁ1 in the exper-
imental IR and Raman spectra, respectively, and a sharp peak at
1725 cmꢁ1 in the calculated IR spectra. In 2, the corresponding
peaks appeared at 1751 and 1793 cmꢁ1 in the experimental spec-
tra and 1721 cmꢁ1 in the DFT-IR spectrum. The bands at 1632
(DFT: 1630) and 1725 (DFT: 1638) cmꢁ1 of 3 in the IR and
Raman spectrum, respectively, were attributed to the stretching
vibrations of the carbonyl group. Chalcone 4 exhibits the same
band structures at 1596 (DFT: 1608) and 1725 (DFT: 1622) cmꢁ1
in the IR and Raman spectra, respectively. It is notable that the
vibrational frequencies in both the IR and Raman experimental
spectra are red-shifted relative to those in the DFT-calculated spec-
tra of the optimized structures of the hydroxy chalcones; this indi-
cates the strong involvement of the 20-hydroxy functional group in
intramolecular hydrogen bonding in the hydroxy chalcone deriva-
tives. Several basic factors such as inductive and mesomeric effects
will significantly shift the carbonyl stretching frequencies in car-
bonyl functional groups in aldehydes and ketones. The vibrational
frequency of this group mainly depends on the force constant,
O–H bond vibrations
As
a
result
of
the
hydrogen bonding in
the
hydroxy-functionalized chalcones, significant deviation between
the experimental and theoretical IR and Raman spectra is expected.
Fig. 4. Normalized absorbance spectra of 1–4 recorded in ethanol as a solvent: experimental (black), TD-DFT (red), and fluorescence (blue). (For interpretation of the
references to colour in this figure legend, the reader is referred to the web version of this article.)

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561
As shown in Figs. 2 and 3, the peaks for the O–H bond vibrations in
the experimental IR and Raman spectra are at very different posi-
tions than those in the theoretical spectra. Broad and strong vibra-
tion peaks are evident at 3350, 3500, 3462, and 3442 cmꢁ1 in the
experimental FT-IR spectra of 1, 2, 3, and 4, respectively; these
indicate the presence of the O–H bond, where the hydrogen atom
is involved in hydrogen bonding with the carbonyl oxygen. The
corresponding peaks in the DFT-IR spectra, in which intramolecu-
lar hydrogen bonding is ignored, are apparent at 3799, 3796,
3739, and 3797 cmꢁ1 for 1, 2, 3, and 4, respectively.
and 3214 cmꢁ1, respectively. The additional peaks at 3164 and
3035 cmꢁ1 in the IR and Raman spectra respectively of chalcone
4 were attributed to the asymmetric and symmetric stretching
vibrations of the methoxy-methyl protons.
UV–visible absorption spectra
UV–visible spectra of the synthesized hydroxy chalcone deriva-
tives in ethanol solution are shown in Fig. 4; theoretical UV–visible
spectra obtained from TD-DFT calculations of the optimized
ground state geometries of 1–4 are also shown for comparison.
The synthesized chalcones contain a hydroxy-substituted aromatic
carbonyl group with continuous conjugation that shows two
C–H vibrations
The C–H bond vibrations can be categorized into two types
based on the nature of the carbon atom: Aliphatic and aromatic.
Chalcone 1 shows characteristic aromatic C–H vibrations at 3216
and 3215 cmꢁ1 in the calculated IR and Raman spectra, respec-
tively. Although most of corresponding peaks in the experimental
IR and Raman spectra overlap with the O–H stretching band, sev-
eral aromatic C–H vibrational peaks due to out-of-plane bending
vibrations are evident at 821 and 847 cmꢁ1 in the experimental
IR and Raman spectra, respectively, and at 843 cmꢁ1 in the
DFT-IR spectrum. For 2, the C–H vibration at 3218 cmꢁ1 in
the DFT-IR spectra is significant, but the corresponding peak in
the experimental spectra is dominated by the O–H vibrational
peak, as is the case for 1. Out-of-plane bending modes in 2 are
apparent at 875 and 894 cmꢁ1 in the experimental data, while
the same peaks are observed at 843 and 847 cmꢁ1 in the
DFT-calculated spectra. For 3 and 4, the C–H vibrations effectively
overlap with the O–H vibrations because of the increased number
of hydroxy groups and resultant peak broadening. In the DFT-IR
and DFT-Raman spectra, the C–H vibrational peaks are at 3205
predominant n ! pꢃ and
p !
pꢃ electronic transitions in the UV–
visible region. The two chromophoric groups at the ends of the
carbonyl group in 1–4 produce the colors of the synthesized com-
pounds, which range from bright yellow (1) to orange-red (4). The
electron-donating hydroxy and methoxy groups are responsible for
promotion of the donor character of the chromophores toward the
carbonyl functional group, which acts as an acceptor. The absorp-
tion maxima of these compounds are evident in the near UV
region, i.e., at 370 (350), 368 (351), 343 (334), and 363 (356) nm
in the experimental (TD-DFT) absorption spectra of chalcones 1,
2, 3, and 4, respectively. The similarity of the absorption maxima
of the experimental and TD-DFT results clearly confirms the accu-
racy of our theoretical method. The slight deviation of the TD-DFT
spectra from the experimental spectra was attributed to the effects
of inter- and intramolecular hydrogen bonding in 1–4, which are
not considered in the theoretical calculations. The small differ-
ences in the absorption spectra of 1–4 indicate that the distribu-
tions of the molecular orbitals (and their relative energies) are
Fig. 5. SEM images of chalcones 1–4: (a) chalcone 1, (b and c) epitaxial growth of the crystals of chalcone 1 after recrystallization in ethanol, (d) chalcone 2, (e) chalcone 3,
and (f) chalcone 4.

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M. Jagadeesh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 150 (2015) 557–564
similar. The energy difference between the ground and excited
states, i.e., the bandgap or highest occupied molecular orbital
(HOMO)–lowest unoccupied molecular orbital (LUMO) gap, was
calculated from the UV–visible absorption spectra. To calculate
the bandgap, the low-energy region of the spectrum (i.e., the
absorption edge) was selected and an imaginary line that intersects
the x-axis on an extrapolation of the linear part of the spectrum
was substituted into the Planck equation, as follows:
these compounds can be considered as D–A–D-type molecules
[43], as shown in the Supplementary data (Fig. S8). In general,
the molecular arrangements in 1–4 strengthen the intramolecular
charge transfers (ICTs).
HOMO–LUMO calculations
The frontier molecular orbitals, which comprise the HOMO and
LUMO, play an important role in the optical and electrical proper-
ties and UV–visible spectra of molecules [44,45]. The optimized
structures (Fig. 1) of chalcones 1–4 were used for visualization of
the HOMO and LUMO orbitals using DFT. The distribution of the
HOMO and LUMO orbitals were computed using the
B3LYP/6-31G(d,p) method at the ground states of the optimized
structures and are shown in Fig. S6 (Supplementary data). In chal-
cones 1 and 4, the HOMO orbitals are primarily concentrated on
ring B, which contains electron-releasing or positive mesomeric
groups like –OH/–OCH3 at the 4-position. In chalcone 2, the
HOMO orbital is evenly distributed between ring A and B because
of the presence of donor groups on both rings. In contrast, chalcone
3 exhibits a different pattern with the HOMO orbitals located only
on ring A because of the absence of such donor groups on ring B.
The LUMO orbitals are primarily distributed on the acceptor part
of the chalcone moieties, i.e., the carbonyl groups [43].
hc
k ðmÞ
EðJÞ ¼
:
ð1Þ
Alternatively, the bandgap (in units of eV) can be obtained
directly from
1239:84187 ðeV nmÞ
E ðeVÞ ¼
ð2Þ
k ðnmÞ
According to the bandgap calculations using Eq. (2), the four
chalcones have bandgap energies between 0.5 and 4.0 eV and are
therefore suitable as semiconductor materials. The experimental
and calculated (given in brackets) bandgaps derived from the
UV–visible spectra were 2.89 (2.90), 2.93 (2.95), 3.04 (3.09), and
3.01 (2.91) eV for compounds 1, 2, 3, and 4, respectively [42].
The low energies of these bandgaps were attributed to the pres-
ence of one or more positive mesomeric substituents (–OH and/or
–OCH3) on the phenyl rings; enhancement of the
p-conjugation
also decreased the bandgap between the HOMO and LUMO orbi-
tals. It is noteworthy that the presence of one or more
electron-donating functional groups in 1–4 facilitates the
electron-transfer process to the carbonyl functional group; thus,
Fluorescence spectra
The normalized fluorescence emission spectra of chalcones 1–4
are shown in Fig. 4. All synthesized chalcone derivatives show
Fig. 6. Thermograms of chalcones 1–4 showing the response to increasing temperature from 20 to 400 °C in a N2 atmosphere.

M. Jagadeesh et al. / Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 150 (2015) 557–564
563
long-range emissions with corresponding emission maxima.
Chalcone 1 exhibits a strong emission band from 700 to 500 nm,
which covers the red to green region, with emission maxima at
624 and 551 nm. On the other hand, 2 and 4 show dual-emission
with emission maxima at 418, 442, and 568 nm for 2 and 417,
435, 555, and 621 nm for 4. In contrast, chalcone 3 only shows a
high emission band at around 419 nm, which indicates suppres-
sion of the low-energy emission. The general dual-emission shapes
of the spectra for 1–4 was attributed to the generation of a local
excited state, which is followed by a photo-induced ICT [43];
however, the mechanism of this process is under debate [46].
The electron push–pull architecture of these molecules is responsi-
ble for the increased fluorescence. The emission colors of the chal-
cones were quantitatively characterized using the Commission
Internationale de l’Éclairage (CIE) chromaticity coordinates.
Fig. S7 (Supplementary data) shows the CIE chromatogram of the
synthesized chalcone derivatives. From the CIE chromatogram, it
is evident that the chalcones emit white light because of the addi-
tive mixing of the emitted color wavelengths; therefore, they are
suitable for the development of organic light-emitting diodes
(OLEDs).
DFT-optimized results at the B3LYP/6-31G(d,p) level. For the first
time, we interpreted and correlated the IR and Raman spectra of
four hydroxy-functionalized chalcones both experimentally and
theoretically. It was determined that the synthesized chalcone
derivatives are semiconducting materials because of their band-
gaps, which were calculated from the absorption spectra, are
between 0.5 and 4.0 eV. Their potential for application in the
development of OLEDs was suggested from their dual and broad
emission bands.
Acknowledgements
This work was financially supported by National Research
Foundation of Korea (NRF) grants funded by the Korean govern-
ment (MEST and MSIP) (2007-0056095, 2012K2A1A2033072,
2013S1A2A2035406, and 2013R1A1A2009575).
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at http://dx.doi.org/10.1016/j.saa.2015.05.085.
Scanning electron microscopy
References
To evaluate the morphologies of the synthesized chalcones, we
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micrometer size range; however, upon treatment with ethanol,
the crystals of chalcone 1 aggregate into a bushy structure because
of epitaxial growth of the crystal from the center, as shown in
Fig. 5(b) and (c). In contrast, chalcone derivatives 2–4 crystallize
into sheets (layers) owing to the enhanced intermolecular
interactions.
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2 and 3 show a number of
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