Unraveling relation between nonlinear absorption and structure of push pull ornamented anthracenyl chalcone derivatives

Article abstract of DOI:10.1016/j.molstruc.2020.128578

Using green chemical method a series of fifteen systematically substituted 3-(9-substituted anthracen-10-yl)-1-(4-phenyl substituted)prop-2-en-1-one derivatives having high nonlinear absorption coefficient have been synthesized. The nonlinear absorption properties of these compounds were studied using nanosecond pulses at 532 nm wavelength. All 15 derivatives are found to show high nonlinear absorption in the range of 35–640 cm/GW. Among these the derivatives with –NO₂ as one of the substitution group show higher nonlinear absorption. The origin of high nonlinear absorption with low linear absorption in the compounds has been attributed to two-step two-photon absorption process. We have shown that the energy bands of these compounds are distributed such that for excitation at 532 nm they have strong nonlinear absorption. These properties of the reported compounds make them a potential candidate for biological imaging and other applications which are based on nonlinear absorption.

Full text of DOI:10.1016/j.molstruc.2020.128578

Journal of Molecular Structure 1219 (2020) 128578
Contents lists available at ScienceDirect
Journal of Molecular Structure
journal homepage: http://www.elsevier.com/locate/molstruc
Unraveling relation between nonlinear absorption and structure of
push pull ornamented anthracenyl chalcone derivatives
,
,
c
,
, c
Amrita Saha a *, Asha Singh b, Rama Chari b 1, J. Jayabalan b
a Department of Chemistry, Assam University, Silchar, 788011, India
b Nano Science Laboratory, Material Science Section, Raja Ramanna Centre for Advanced Technology, Indore, 452013, India
c Homi Bhabha National Institute, Training School Complex, Anushakti Nagar, Mumbai, 400094, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Using green chemical method a series of fifteen systematically substituted 3-(9-substituted anthracen-
10-yl)-1-(4-phenyl substituted)prop-2-en-1-one derivatives having high nonlinear absorption coefficient
have been synthesized. The nonlinear absorption properties of these compounds were studied using
nanosecond pulses at 532 nm wavelength. All 15 derivatives are found to show high nonlinear absorption
in the range of 35e640 cm/GW. Among these the derivatives with eNO2 as one of the substitution group
show higher nonlinear absorption. The origin of high nonlinear absorption with low linear absorption in
the compounds has been attributed to two-step two-photon absorption process. We have shown that the
energy bands of these compounds are distributed such that for excitation at 532 nm they have strong
nonlinear absorption. These properties of the reported compounds make them a potential candidate for
biological imaging and other applications which are based on nonlinear absorption.
Received 23 March 2020
Received in revised form
14 May 2020
Accepted 30 May 2020
Available online 12 June 2020
Keywords:
Chalcones
Nonlinear absorption
Nonlinear optics
© 2020 Elsevier B.V. All rights reserved.
1. Introduction
nonlinearity is the delocalization of these electrons [15,16]. The
nonlinearity of a compound can be directly correlated to the
Nonlinear optical properties of organic molecules including
chalcone derivatives are being studied for applications like two-
photon fluorescence excitation microscopy, two-photon up-con-
version lasing, 3D nano/microfabrication, and photodynamic ther-
apy etc. [1e14]. For such applications, molecules with high
nonlinear absorption cross-sections with low linear absorption are
required. To design compounds with such optimized properties it is
essential to understand the correlation between the energy level
structure of the compound and its optical response. In principle it is
possible to theoretically calculate the optical response of the
designed molecule. However, these calculations are complex and
computationally demanding and the calculated results would still
have to be verified by experiments [15]. Therefore, preparing a set
of compounds with specific systematic changes in the structure and
measuring the optical properties is a more direct way to under-
stand the correlation between the structure of a compound and
optical response.
number of
the nonlinear coefficient of these compound is normally divided by
the number of -electrons in order to have an idea of the effect of
other factors [15,16]. In principle it is possible to have a large
nonlinear optical response by designing the molecule to have a
p-electrons in it. Due to this scaling with p-electrons,
p
large number of
p-electrons. However it is also desirable to mini-
mize the size of the molecule so that it can be densely packed for
device applications. Hence it is essential to design and optimize
other properties of the compound also in order to maximize the
nonlinear response with the smallest possible size.
Attaching a electron donor (D) and/or electron acceptor (A), to a
compound is one of the effective ways to improve its nonlinear
optical response [17e22]. Different configurations like D-
p-A, D-p-
A- -D and D- -A- -A are being studied extensively for their
p
p
p
contribution to nonlinear optical properties as well as for other
applications [17e19,22]. Further, the position of the D and/or A in
the compound as well as its donating or accepting strength are
known to affect the nonlinear optical response [17,20,21]. Based on
the “isolated molecule approach”, the electronic effect that a sub-
stituent can exert on the compound can be broadly classified into
either a resonance or an inductive effect. The resonance effect oc-
In compounds having
p-electrons, the primary origin of
* Corresponding author.
E-mail address: amrieta06@gmail.com (A. Saha).
Currently Retired.
curs through p-electrons while the inductive effect occurs through
1
https://doi.org/10.1016/j.molstruc.2020.128578
0022-2860/© 2020 Elsevier B.V. All rights reserved.

2
A. Saha et al. / Journal of Molecular Structure 1219 (2020) 128578
s
-electrons. Substituted groups like eOCH3 and eNO2 interact with
intermediate compound S17 was prepared by the Wittig reaction, a
one step alkene-forming reaction, on S16 with reasonable yield.
This process is shown as B in Fig. 1. The compounds S18 and S21
were prepared by Vilsmeier Haack reaction on S17 and S20
respectively with modest yields which are shown as process C in
Fig. 1. Methylation of the compound S19 with dimethyl sulphate,
using phase transfer catalyst, furnished S20 (process D). The
detailed preparation procedure of these compounds and the
structure estimated from 1H NMR, 13C NMR, IR, and ESI-HRMS
measurements are given below. The spectra of some of the syn-
thesized chalcones shows presence of both E and Z forms. Their
corresponding ratio has also been mentioned in the corresponding
synthesis and characterization portion of the compound.
(E)-3-(anthracen-10-yl)-1-(4-chlorophenyl)prop-2-en-1-one
(S01): A solution of 50% NaOH (w/v) was added to a mixture of 4-
chloroacetophenone (1 mmol, 155 mg) and commercially avail-
able 9-anthracenecarboxaldehyde (1 mmol, 206 mg) (S16) in 75 ml
of methanol. The mixture was refluxed with continuous stirring for
6 h and then refrigerated overnight. The reaction mixture was
neutralized with concentrated HCl. The obtained precipitate was
collected by filtration and purified by column chromatography on
silica gel (60e120 mesh) using (EtOAc: Hexane ¼ 25:1) as the
eluent. Yield: 272 mg (70%). mp 132e134oC. IR (KBr, cmꢀ1): 3048
an aromatic compound through a resonance effect by donating an
electron or withdrawing an electron respectively. On the other
hand, substitution of eCH3, a electron donating group, leads to
interaction via s-electrons (inductive effect). Halogen substitutions
are known to interact with the base compound via both resonance
as well as inductive effects [17e22]. However, systematic studies on
linear as well as nonlinear properties of chalcones by changing the
attached groups R1 and R2 (See Fig. 1) of different D or A properties,
in an R1-p-A-p-R2 configuration are not available.
In this article, we present the synthesis procedure and nonlinear
absorption properties of a series of fifteen new anthracene-based
chalcone derivatives (labeled S01 to S15). This series of com-
pounds can be further divided into three sub-series according to
the group attached in the 9th position of the anthracene skeleton.
The general structure of these compounds under study can also be
categorized into two basic structural families of D-
-A- -D. We have targeted anthracene, as it is one of the most
attractive centers; it is planar as well as an excellent fluorophore
[23,24]. Compounds containing the anthracene moiety have ample
advantages over many other -centers and are being widely
p-A-p-D and A-
p
p
p
p
studied for their nonlinear optical properties [9,25e29]. Moreover,
chalcone derivatives have the eC]O group as acceptor and are well
known for their NLO properties like second harmonic generation
and lasing [20,30]. Our focus is investigate the dependence of the
third-order optical nonlinearity, specially the nonlinear absorption
coefficient, on substituents like -Cl, -Br, eNO2, eCH3, eOCH3.
(Ar-CH), 1655 (C]O). 1H NMR (400 MHz, CDCl3):
d 8.84 (d,
J ¼ 16 Hz, 1H), 8.51 (s, 1H), 8.30 (d, J ¼ 8 Hz, 2H), 8.07e8.03 (m, 4H),
7.94 (d, J ¼ 16 Hz, 1H), 7.56e7.50 (m, 5H), 7.44 (d, J ¼ 8 Hz, 1H). 13
C
NMR (CDCl3): d 189.09, 142.21, 136.02, 131.11, 130.20, 129.93, 128.91,
128.83, 128.38, 125.30, 125.01. ESI-HRMS [M þ H]þ calcd for
C
23H16ClO m/z 343.0884, found 343.0864.
The 1H NMR (400 MHz) spectrum of S01 in CDCl3 solvent is
2. Synthesis procedure and experimental details
shown in Fig. SI-10 and its structure with the protons designated as
Ha and Hb is shown in the inset of Fig. SI-10. A doublet with
E/Z-3-(9-substitutedanthracen-10-yl)-1-(4-phenylsubstituted)
prop-2-en-1-one derivatives have been synthesized by Claisen-
Schmidt condensation (process A) as shown in Fig. 1. The
J ¼ 16 Hz, centered at
d
¼ 8.84 ppm is observed for the Ha proton,
Fig. 1. Scheme: Reagents and conditions: (A) 50% NaOH in Methaol, 60 ꢁC; (B) HOCH2CH2OCH2CH2OCH2CH2OH, NH2NH2, aq. KOH, 200 ꢁC, 80%. (C) DMF, C6H4Cl2, POCl3, 100e110 oC,
(18) 52%, (21) 60%; (D) (CH3)2SO4, aq. NaOH, CH2Cl2, C13H22ClN, r.t, 85%; The general structure of all the compounds and the groups attached are also shown in the top right corner.

A. Saha et al. / Journal of Molecular Structure 1219 (2020) 128578
3
another doublet with J ¼ 16 Hz, centered at 7.94 ppm is observed
for the Hb proton. This confirms the trans configuration of the
compound. Fig. SI-11 is the 13C NMR (100 MHz, CDCl3) spectrum of
A 50% NaOH (w/v) solution was added to a mixture of 4-
chloroacetophenone (1 mmol, 155 mg) and (S18) (1 mmol,
220 mg) in 25 ml of methanol. The mixture was refluxed with
continuous stirring for 6 h and then refrigerated overnight. The
reaction mixture was neutralized with concentrated HCl and pre-
cipitate obtained was collected by filtration and purified using
column chromatography on silica gel (60e120 mesh) using (EtOAc:
Hexane ¼ 1: 20), trans 20%. Yield: 192 mg (54%). mp 139e141oC. 1H
S01.
d
¼ 189.09 ppm for the carbonyl carbon. Fig.SI-12 displays the
mass spectrum. ESI-HRMS [M þ H]þ calculated for S01 [C23H16ClO]
m/z is 343.0884 from measurement it comes out to 343.0864. The
structure of all other compounds were also confirmed by following
a similar procedure. The spectra of all these samples are also pre-
sented in the Supporting Information (S$I).
NMR (400 MHz, CDCl3):
d
8.38 (d, J ¼ 12 Hz, 1H), 8.35e8.31 (M, 4H),
(E)-3-(anthracen-10-yl)-1-(4-bromophenyl)prop-2-en-1-one
(S02): S02 was synthesized from S16 (1 mmol, 206 mg) and 4-
bromoacetophenone (1 mmol, 199 mg) by the same procedure as
described for S01 except that the reaction time was 7 h. The product
was purified by column chromatography on silica gel (60e120
mesh) using (EtOAc: Hexane ¼ 25: 1) as the eluent. Yield: 309 mg
(80%). mp 149e151oC. IR (KBr, cmꢀ1): 3046 (Ar-CH), 1662 (C]O). 1H
8.04 (d, J ¼ 8 Hz, 2H), 7.82 (d, J ¼ 8 Hz, 2H), 7.57 (d, J ¼ 8 Hz, 2H), 7.52
(d, J ¼ 8 Hz, 2H), 7.48 (d, J ¼ 12 Hz, 1H), 3.17 (s, 3H). 13C NMR
(CDCl3):
d 188.29, 143.08, 140.37, 139.44, 130.38, 130.03, 129.72,
129.40, 129.25, 129.14, 128.99, 128.61, 128.51, 127.75, 125.86, 125.30,
125.19, 125.07, 124.93, 124.01, 14.42, 14.11. ESI-HRMS [M þ H]þ calcd
for C24H18ClO m/z 357.1041, found 357.1049.
(Z)-1-(4-bromophenyl)-3-(9-methylanthracen-10-yl)prop-2-
en-1-one (S07): S07 was synthesized from S18 (1 mmol, 220 mg)
and 4-bromoacetophenone (1 mmol, 199 mg) by the same pro-
cedure as described for S06. The product was purified by column
chromatography on silica gel (60e120 mesh) using (EtOAc:
Hexane ¼ 1: 20) as the eluent. Yield: 236 mg (59%). mp 190e192oC.
IR (KBr, cmꢀ1): 3026 (Ar-CH), 1666 (C]O). 1H NMR (400 MHz,
NMR (400 MHz, CDCl3):
d
8.83 (d, J ¼ 16 Hz,1H), 8.50 (s,1H), 8.30 (d,
J ¼ 8 Hz, 2H), 8.05 (d, J ¼ 8 Hz, 2H), 7.96 (d, J ¼ 8 Hz, 2H), 7.67 (d,
J ¼ 8 Hz, 2H), 7.58e7.52 (m, 5H). 13C NMR (CDCl3):
d 188.34, 142.30,
136.45, 131.92, 131.13, 130.20, 130.06, 129.50, 128.85, 128.53, 128.42,
126.42, 125.03 ppm. ESI-HRMS [M þ H]þ calcd for C23H16BrO m/z
387.0379, found 364.0363.
(E)-3-(anthracen-10-yl)-1-(4-nitrophenyl)prop-2-en-1-one
(S03): S03 was synthesized from S16 (1 mmol, 206 mg) and 4-
nitroacetophenone (1 mmol, 165 mg) by the same procedure as
described for S01 except that the reaction time was 2 h. The product
was purified by column chromatography on silica gel (60e120
mesh) using (EtOAc: Hexane ¼ 25: 1) as the eluent. Yield: 307 mg
(87%). mp 142e144oC. IR (KBr, cmꢀ1)): 3041 (Ar-CH), 1657 (C]O).
CDCl3):
d
8.26 (d, J ¼ 8 Hz, 2H), 8.09 (d, J ¼ 8 Hz, 2H), 8.00 (d,
J ¼ 8 Hz, 1H), 7.51e7.44 (m, 5H), 7.29 (d, J ¼ 8 Hz, 2H), 7.08 (d,
J ¼ 8 Hz, 2H), 3.06 (s, 3H). 13C NMR (CDCl3):
d 192.14, 140.38, 138.26,
130.73, 130.47, 129.45, 128.71, 129.24, 125.92, 125.44, 125.14, 124.98,
14.19. ESI-HRMS [M þ H]þcalcd for C24H18BrO m/z 401.0536, found
401.0538.
(E)-3-(9-methylanthracen-10-yl)-1-(4-nitrophenyl)prop-2-en-
1-one (S08): S09 was synthesized from S18 (1 mmol, 220 mg) and
4-nitroacetophenone (1 mmol, 165 mg) by the same procedure as
described for S06 except that the reaction time was 1 h. The product
was purified by column chromatography on silica gel (60e120
mesh) using (EtOAc: Hexane ¼ 1: 10) as the eluent. Yield: 300 mg.
(78%). mp 172e174oC. IR (KBr, cmꢀ1): 3031(Ar-CH), 1658 (C]O). 1H
1H NMR (400 MHz, CDCl3):
d
8.90 (d, J ¼ 16 Hz,1H), 8.53 (s,1H), 8.38
(d, J ¼ 8 Hz, 2H), 8.29 (d, J ¼ 8 Hz, 2H), 8.23 (d, J ¼ 8 Hz, 2H), 8.07 (d,
J ¼ 8 Hz, 2H), 7.58 (m, 5H). 13C NMR (CDCl3):
d 188.07, 149.65,
143.85, 142.53, 131.24, 129.97, 129.66, 129.13, 129.77, 125.51, 124.51,
124.90, 123.91. ESI-HRMS [M þH]þ calcd for C23H16NO3 m/z
354.1125, found 354.1124.
(E)-3-(anthracen-10-yl)-1-(4-methoxyphenyl)prop-2-en-1-
one (S04): S04 was synthesized from S16 (1 mmol, 206 mg) and 4-
methoxyacetophenone (1 mmol, 150 mg) by the same procedure as
described for S01 except that the reaction time was 3 h. The product
was purified by column chromatography on silica gel (60e120
mesh) using (EtOAc: Hexane ¼ 25: 1) as the eluent. Yield: 262 mg
NMR (400 MHz, CDCl3):
d
8.91 (d, J ¼ 16 Hz, 1H), 8.39e8.36 (m, 4H),
8.32 (d, J ¼ 8 Hz, 2H), 8.22 (d, J ¼ 8 Hz, 2H), 7.54e7.60 (m, 4H), 7.51
(d, J ¼ 16 Hz, 1H), 3.17 (s, 3H). 13C NMR (CDCl3):
d 187.71, 149.78,
144.20,142.27,132.76,129.66,129.20, 127.60, 125.82, 125.53, 125.33,
125.08, 124.99, 123.54, 14.25. ESI-HRMS [M þ H]þ calcd for
C24H18NO3 m/z 368.1281, found 368.1283.
(78%). mp 114e116oC. 1H NMR (400 MHz, CDCl3):
d
8.79 (d,
(E)-3-(9-methylanthracen-10-yl)-1-(4-methoxyphenyl)prop-
J ¼ 16 Hz, 1H), 8.47 (s, 1H), 8.33 (d, J ¼ 8 Hz, 2H), 8.10 (d, J ¼ 8 Hz,
2-en-1-one (S09): S09 was synthesized from S18 (1 mmol, 220 mg)
and 4-methoxyacetophenone (1 mmol, 150 mg) by the same pro-
cedure as described for S06 except that the reaction was refluxed
for 7 h and stirred at room temperature for 5 h. The product was
purified by column chromatography on silica gel (60e120 mesh)
using (EtOAc: Hexane ¼ 40: 1) as the eluent. trans 75%. Yield:
2H), 8.04 (d, J ¼ 8 Hz, 2H), 7.57 (d, J ¼ 16 Hz, 1H), 7.53e7.51 (m, 4H),
7.00 (d, J ¼ 8 Hz, 2H), 3.89 (s, 3H). 13C NMR (CDCl3):
d 187.56,163.39,
140.66, 131.04, 130.80, 130.66, 130.17, 129.37, 128.68, 128.02, 126.11,
125.17, 124.84, 113.73, 112.98, 55.21. ESI-HRMS [M þ H]þ calcd for
C24H19O2 m/z 339.1380, found 339.1381.
(E)-3-(anthracen-10-yl)-1-phenylprop-2-en-1-one (S05): S05
was synthesized from S16 (1 mmol, 206 mg) and acetophenone
(1 mmol, 120 mg) by the same procedure as described for S01
except that the reaction time was 4 h. The product was purified by
column chromatography on silica gel (60e120 mesh) using (EtOAc:
Hexane ¼ 25: 1) as the eluent. Yield: 206 mg (67%). mp 120e122oC.
IR (KBr, cmꢀ1): 3049 (Ar-CH), 1655 (C]O). 1H NMR (400 MHz,
235 mg. (67%). mp 159e161oC. 1H NMR (400 MHz, CDCl3):
d 8.80 (d,
J ¼ 16 Hz, 1H), 8.36 (t, J ¼ 8 Hz, 2H), 8.10 (d, J ¼ 8 Hz, 2H), 7.57e7.50
(m, 5H), 7.00 (d, J ¼ 8 Hz, 2H), 3.90 (s, 3H), 3.17 (s, 3H). 13C NMR
(CDCl3):
d 188.23, 163.89, 142.02, 132.25, 131.32, 130.07, 129.58,
126.45, 125.99, 125.60, 125.45, 114.24, 55.79, 14.72. ESI-HRMS [M þ
H]þ calcd for C25H21O2 m/z 353.1536, found 357.1541.
(Z)-3-(9-methylanthracen-10-yl)-1-phenylprop-2-en-1-one
(S10): S10 was synthesized from S18 (1 mmol, 220 mg) and ace-
tophenone (1 mmol, 120 mg) by the same procedure as described
for S06 except that the reaction time was 4 h. The product was
purified by column chromatography on silica gel (60e120 mesh)
using (EtOAc: Hexane ¼ 1: 10) as the eluent. Yield: 58%. mp
125e127oC. IR (KBr, cmꢀ1): 2932 (Ar-CH), 1660 (C]O). 1H NMR
CDCl3):
d
8.82 (d, J ¼ 16 Hz, 1H), 8.48 (s, 1H), 8.33 (d, J ¼ 8 Hz, 2H),
8.11 (d, J ¼ 8 Hz, 2H), 8.05 (d, J ¼ 8 Hz, 2H), 7.59 (d, J ¼ 16 Hz, 2H),
7.54e7.52 (m, 5H). 7.62 (d, J ¼ 8 Hz, 1H). 13C NMR (CDCl3):
d 189.43,
141.67, 132.92, 131.06, 130.76, 129.88, 129.42, 128.55, 128.29, 126.25,
126.22, 125.06. ESI-HRMS [M þ H]þ calcd for C23H17O m/z 309.1274,
found 309.1273.
(E)-1-(4-chlorophenyl)-3-(9-methylanthracen-10-yl)prop-2-
en-1-one (S06): 9-methylanthracene-10-carbaldehyde (S18) was
synthesized in aqueous KOH solution and hydrazine hydrate
following the reported procedure from commercially available S16.
(400 MHz, CDCl3):
d
8.36 (d, J ¼ 8 Hz, 2H), 8.26 (d, J ¼ 8 Hz, 2H), 8.14
(d, J ¼ 8 Hz, 2H), 8.11 (d, J ¼ 8 Hz, 2H), 7.93 (d, J ¼ 12 Hz, 1H), 7.48 (d,
J ¼ 8 Hz, 2H), 7.45 (d, J ¼ 12 Hz, 1H), 7.52e7.56 (m, 3H), 3.05 (s, 3H).
E: Z ¼ 47: 53.13C NMR (CDCl3):
d 192.18, 142.59, 140.16, 132.21,

4
A. Saha et al. / Journal of Molecular Structure 1219 (2020) 128578
130.34, 129.48, 128.71, 128.02, 127.79, 126.11, 125.79, 125.20, 124.90,
14.43, 14.12. ESI-HRMS [M þ H]þ calcd for C25H21O m/z 323.1430,
found 323.1438.
purified by column chromatography on silica gel (60e120 mesh)
using (EtOAc: Hexane ¼ 1: 4) as the eluent. Yield: 250 mg (74%). mp
120e122oC. IR (KBr, cmꢀ1): 3069 (Ar-CH), 1663 (C]O). 1H NMR
(E)-1-(4-chlorophenyl)-3-(9-methoxyanthracen-10-yl)prop-2-
en-1-one (S11): S11 was synthesized from S21 (1 mmol, 236 mg)
and 4-bromoacetophenone (1 mmol, 199 mg) by the same pro-
cedure as described for S12. The product was purified using column
chromatography on silica gel (60e120 mesh) using (EtOAc:
Hexane ¼ 1: 4), Yield: 193 mg (52%). mp 138e140oC. IR (KBr, cmꢀ1):
(400 MHz, CDCl3):
d
8.80 (d, J ¼ 16 Hz, 1H), 8.40e8.34 (m, 4H), 8.39
(d, J ¼ 8 Hz, 2H), 8.35 (d, J ¼ 8 Hz, 2H), 8.10 (d, J ¼ 8 Hz, 1H), 7.62 (d,
J ¼ 8 Hz, 1H), 7.59e7.53 (m, 5H), 4.19 (s, 3H). 13C NMR (CDCl3):
d
191.87, 189.68, 183.07, 159.14, 153.58, 141.73, 137.92, 134.05,
133.83, 133.43, 133.02, 130.69, 130.56, 129.29, 128.72, 127.16, 126.57,
125.62, 123.90, 122.75, 63.39. ESI-HRMS [M þ H]þ calcd for
3056 (Ar-CH), 1657 (C]O). 1H NMR (400 MHz, CDCl3):
d
8.80 (d,
C24H19O2 m/z 339.1380, found 339.1404.
J ¼ 16 Hz, 1H), 8.39 (d, J ¼ 8 Hz, 1H), 8.34e8.32 (m, 4H), 8.03 (d,
J ¼ 8 Hz, 1H), 7.83e7.80 (m, 3H), 7.56e7.49 (m, 4H), 4.19 (s, 3H). 13
C
2.1. Measurement of nonlinear absorption
NMR (CDCl3):
d 188.30, 153.75, 142.24, 139.45, 136.21, 134.02,
130.59, 130.03, 129.02, 127.13, 126.67, 125.92, 125.50, 125.33, 124.24,
Z-scan measurements were carried out with linearly polarized
Q-switched Nd-YAG laser of pulse width 28 ns (full width at half
maximum). The fundamental of the laser beam 1.064 mm or the
24
122.79, 63.39. ESI-HRMS [M þ H]þ calcd for C24
H ClO2 m/z
18
373.0990, found 373.0989.
(E)-1-(4-bromophenyl)-3-(9-methoxyanthracen-10-yl)prop-2-
en-1-one (S12): 10-methoxy 9-anthraldehyde (S21) was prepared
according to the known procedure. Anthrone (S19) on methylation
with dimethyl sulphate provides 9-methoxyanthracene (S20). S20
on Vilsmeier reaction with dimethyl formamide and phosphorus
oxychloride yields S21. A 50% NaOH (w/v) solution was added to a
mixture of 4-chloroacetophenone (1 mmol, 155 mg) and (S21)
(1 mmol, 236 mg) in 125 ml of methanol. The mixture was refluxed
with continuous stirring for 3 h and then refrigerated overnight.
The reaction mixture was neutralized with concentrated HCl. The
product was purified by column chromatography on silica gel
(60e120 mesh) using (EtOAc: Hexane ¼ 1: 4) as the eluent. Yield:
second harmonic of the laser beam at 532 nm was used for the z-
scan measurements. The laser pulse energy was adjusted in the
range of 30 mJe400 mJ by using neutral density filters. The pulse
energy for a given sample was chosen such that the lowest trans-
mission in z-scan remains near 0.5. This is because if the overall
change in transmission is too high, pump-depletion effects and
contributions of higher-order nonlinear effects might also become
significant, complicating the analysis of the results [31]. The laser
was operated at 1 Hz repetition rate to avoid thermal effects. For
the z-scan measurements these compounds were dissolved in
chloroform and kept in a 1 mm path-length flow quartz cell (con-
centration: 1.3 ꢂ 10ꢀ8 M). The sample was circulated in the cell to
avoid any thermal induced damage to it. Further, the stability of the
compounds throughout the measurement was ensured by checking
that the linear absorption spectra before and after the z-scan
measurements remain the same.
308 mg (74%). mp 155e157oC. 1H NMR (400 MHz, CDCl3):
d 8.81 (d,
J ¼ 16 Hz,1H), 8.40e8.37 (m, 1H), 8.33 (m, 4H), 7.96 (d, J ¼ 8 Hz, 2H),
7.82 (d, J ¼ 8 Hz, 2H), 7.67 (d, J ¼ 8 Hz, 1H), 7.57e7.54 (m, 2H), 7.51
(d, J ¼ 16 Hz, 1H), 4.19 (s, 3H). 13C NMR (CDCl3):
d 188.56, 153.78,
134.22, 134.12, 133.48, 132.15, 132.05, 130.62, 130.29, 130.17, 130.04,
127.22, 126.83, 126.72, 125.63, 125.53, 124.27, 122.93, 122.82. ESI-
HRMS [M þ H]þ calcd for C24H18BrO2 m/z 417.0485, found 417.0490.
(E)-3-(9-methoxyanthracen-10-yl)-1-(4-nitrophenyl)prop-2-
en-1-one (S13): S13 was synthesized from S21 (1 mmol, 236 mg)
and 4-nitroacetophenone (1 mmol, 165 mg) by the same procedure
as described for S12 except that the reaction time was 2 h. The
product was purified by column chromatography on silica gel
(60e120 mesh) using (EtOAc: Hexane ¼ 25: 1) as the eluent. Yield:
325 mg (85%). mp 195e197oC. IR (KBr, cmꢀ1): 3071 (Ar-CH), 1664
3. Results and discussions
In Fig. 2 we show the linear absorption spectra of all the com-
pounds. In the absorption spectra there are two well distinguish-
able peaks, one in the wavelength range 250e265 nm and another
weak peak in the wavelength range 390e425 nm. In table- 1 the
peak wavelengths in absorption spectra, labs, of the compounds in
these two wavelength range are tabulated. The origin of these two
peaks in compounds containing carbonyl group can be attributed to
(C]O). 1H NMR (400 MHz, CDCl3):
d
8.88 (d, J ¼ 16 Hz, 1H), 8.38 (d,
the well known
p
ꢀ
p* (stronger) and n ꢀ p* (weaker) transitions
J ¼ 8.0 Hz, 2H), 8.34e8.31 (m, 2H), 8.23 (d, J ¼ 12.0 Hz, 2H), 7.54 (d,
J ¼ 16 Hz, 1H), 7.58 (d, J ¼ 8 Hz, 4H), 4.20 (s, 3H). 13C NMR (CDCl3):
respectively [32]. Although the nitro derivatives (R1 ¼ eNO2) also
have these two peaks, the peak in the longer wavelength regime is
clearly red-shifted to the 437e454 nm regime when compared to
the other compounds. Such red-shift can be attributed to the strong
electron withdrawing nature of the eNO2 group [33,34]. Among the
compounds having eNO2 group the compound S08 has the highest
red-shift of n ꢀ p* transition. Some of the compounds also show
several small peaks in the wavelength range 300e400 nm; these
are due to the vibrational fine structure [35,36]. Note that all the
compounds are nearly transparent for wavelengths longer than
520 nm. There may be a very small linear absorption present in
some of the samples, still the transmission loss through the sample
was less than 1%, the detection limit of our spectrograph.
d
188.11, 156.17, 154.25, 143.72, 142.68, 130.74, 129.56, 126.98,
125.44, 125.30, 124.31, 123.93, 122.94, 63.50. ESI-HRMS [M þ H]þ
calcd for C24H18NO4 m/z 384.1230, found 384.1233.
(E)-3-(9-methoxyanthracen-10-yl)-1-(4-methoxyphenyl)prop-
2-en-1-one (S14): S14 was synthesized from S21 (1 mmol, 236 mg)
and 4-methoxyacetophenone (1 mmol, 150 mg) by the same pro-
cedure as described for S12 except that the reaction was refluxed
for 7 h and stirred at rt for 5 h. The product was purified by column
chromatography on silica gel (60e120 mesh) using (EtOAc:
Hexane ¼ 40: 1) as the eluent. Yield: 257 mg (70%). mp 170e172oC.
E: Z ¼ 66: 34 1H NMR (400 MHz, CDCl3):
d
8.77 (d, J ¼ 16 Hz, 1H),
8.36 (t, J ¼ 8 Hz, 4H), 8.10 (d, J ¼ 8 Hz, 2H), 7.57e7.53 (m, 4H), 7.45
(m, 2H), 7.00 (d, J ¼ 8 Hz, 1H), 4.19 (s, 3H), 3.90 (s, 3H). 13C NMR
The emission spectra of the compounds were measured by
exciting at wavelengths near their absorption peaks. Fig. 3 shows
the emission spectra of some of the compounds, S03, S08 and S13.
The emission spectra for the rest of the compounds and the emis-
sion spectra when excited at different absorption peaks are in SI
(Fig.SI-1 to Fig.SI-3). The excitation wavelengths and the corre-
sponding peak wavelength of the emission for all the compounds
are tabulated in table- 1. Note that the emission spectra for all the
(CDCl3):
d 187.90, 163.55, 153.35, 140.85, 130.96, 130.61, 130.49,
1126.44, 125.69, 125.27, 124.19, 122.66, 113.90, 63.33, 55.44. ESI-
HRMS [M þ H]þ calcd for C25H21O3 m/z 369.1485, found 369.1507.
(E)-3-(9-methoxyanthracen-10-yl)-1-phenylprop-2-en-1-one
(S15): S15 was synthesized from S21 (1 mmol, 236 mg) and ace-
tophenone (1 mmol, 120 mg) by the same procedure as described
for S12 except that the reaction time was 7 h. The product was

A. Saha et al. / Journal of Molecular Structure 1219 (2020) 128578
5
Fig. 2. Linear absorption spectra of all the compounds in the three different series: (a) S01 to S05, (b) S06 to S10 and (c) S11 to S15. Inset shows the same in expanded scale. The
general structure of the compound is also shown in the inset.
Table 1
Linear optical properties of the chalcone derivatives (S01eS15). labs: main absorp-
dI
dz
tion peak wavelengths; lem: Peak emission wavelength along with the excitation
(Ex) wavelength; lst: Amount of Stokes shift between absorption and emission
peaks.
¼ ꢀ a0I ꢀ
b
I2;
(1)
where a0 is the linear absorption coefficient and
b
is the nonlinear
Compound
labs (nm)
lem (nm)
lst (nm)
absorption coefficient related to the imaginary part of third-order
susceptibility of the sample. At a location of the sample z, the in-
tensity distribution (I), having Gaussian nature in space (r) and time
(t) at the entrance of the cell can be expressed as,
S01 (R1 ¼ -Cl)
260, 415
253, 418
257, 437
257, 390
NA, 415
255, 399
261, 399
261, 454
NA, 400
261, 399
251, 421
259, 421
258, 451
258, 433
256, 419
302 (Ex 258)
532 (Ex 416)
567 (Ex 437)
523 (Ex 390)
528 (Ex 414)
430 (Ex 399)
436 (Ex 392)
525 (Ex 455)
399 (Ex 258)
531 (Ex 391)
547 (Ex 327)
535 (Ex 424)
543 (Ex 449)
538 (Ex 432)
296 (Ex 258)
42
S02 (R1 ¼ -Br)
S03 (R1 ¼ eNO2)
S04 (R1 ¼ eOCH3)
S05 (R1 ¼ eH)
S06 (R1 ¼ -Cl)
114
130
133
113
31
ꢀ
h
i
Iðr; t; zÞ ¼ I0
2exp
u0
S07 (R1 ¼ -Br)
S08 (R1 ¼ eNO2)
S09 (R1 ¼ eOCH3)
S10 (R1 ¼ eH)
S11 (R1 ¼ -Cl)
37
71
u
ðzÞ
sffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
ꢃ
ꢄ ꢅ
ꢃ
ꢄ
e
2
2
ꢁ
ꢂ
ꢀ 2
2 ꢀ
; where
u
ðzÞ ¼ u0 1 þ
;
r
ðzÞ
t
t0
z
z0
132
126
114
92
105
40
u
S12 (R1 ¼ -Br)
S13 (R1 ¼ eNO2)
S14 (R1 ¼ eOCH3)
S15 (R1 ¼ eH)
z0 is the Rayleigh range given by z0
¼
pu20
=l, l is the wavelength of
light used, u0 is the beam waist and t0 is the pulse width. Using Eq.
(1) and Eq.3 the energy of the pulse transmitted through the
sample can be obtained by integration over space and time and is
given by Ref. [43],
compounds are Stokes shifted with respect to the absorption peak
and are also listed in table- 1. Apart from the basic structure of the
compound, the magnitude of Stokes shift depends on factors such
as electron donating or withdrawing property of the substituent
group, properties of the solvent and whether the excited state can
undergo any specific interactions such as charge transfer or energy
transfer [37e41]. A large Stokes shift observed for most of the
present compounds indicates that the environment is not rigid and
rearrangement is possible.
∞
ð
h
ꢁ
ꢂi
1
TðzÞ ¼
ln 1 þ qð0; 0; zÞexp ꢀt2
dt:
(2)
pffiffiffi
p
qð0; 0; zÞ
ꢀ∞
Here qðr; t; zÞ ¼
b
Iðr; t; zÞL and L is the thickness of the sample.
Fig. 4 also shows the best fit curve obtained for these three samples
(see Fig.SI-4 and Fig.SI-5 for other samples). The obtained best fit
values of
b for all the samples are tabulated in table- 2. In com-
Fig. 4 shows the open aperture z-scan curves for three com-
pounds S03, S08 and S13. The other compounds also shows similar
z-scan curves which are given in SI (Fig.SI-4 and Fig.SI-5). When the
sample is kept well away from focus where the intensity is low, the
transmission through all the samples is ꢃ 1.0. This is due to the fact
that at 532 nm all the samples have negligible linear absorption.
However, as the sample is moved closer to the focus (z ¼ 0) the
transmission through the sample reduces, indicating that the ab-
sorption in the sample increases with intensity. The incremental
change in the intensity (dI) after propagating a small distance dz in
the sample having linear and third-order nonlinear absorption is
given by [42].
parison with the reported nonlinear absorption for various mole-
cules in the literature (including most of the references presented
here) the present set of compounds can be clearly classified among
those having a large nonlinear absorption coefficient.
In the set of 15 compounds studied here, the base structure
remains same and the substitutions R1 and R2 are changed in each
sample. As mentioned before, they can be classified into three sub-
series of compounds (S01eS05, S06eS10, and S11eS15) based on
the group attached in the anthracenyl 9-position (R2). These groups
have an increasing electron donor strength in the order eH /
eCH3 / eOCH3. The substitutions used at the other end of the
compound (R1) are electron withdrawing functional groups -Cl, -Br,

6
A. Saha et al. / Journal of Molecular Structure 1219 (2020) 128578
Table 2
Nonlinear absorption coefficient values for samples S01 e S15. The nonlinear absorption coefficient (b) is specified in the unit of cm/GW.
Compound
S01
Structure
b
Compound
S06
Structure
b
Compound
S11
Structure
b
70
330
52
S02
S03
90
S07
S08
360
640
S12
S13
38
550
350
S04
S05
180
300
S09
S10
55
34
S14
S15
120
35
Fig. 4. Open aperture z-scan data of samples S03, S08 and S13 at 532 nm. Scatters are
the experimental data and lines are the best fit curves with Eq. (2).
Fig. 3. Normalized one photon emission spectra for S03, S08 and S13 in chloroform
when excited at 437, 455 and 499 nm respectively.
the compound.
From Fig. 5 we see that among the compounds studied here the
ones having eNO2 as the substitution R1 show a large nonlinear
absorption coefficient irrespective of the substitution at R2. Further,
for compounds having an electron withdrawing nature at R1, the
-Cl, -Br and eNO2, an increased nonlinear absorption is observed
when R2 is eCH3. The nonlinear response of a compound has been
shown to increase with donor/acceptor strength in D-A-D and D-A-
A type molecules [20,21]. In the present case attaching an even
stronger electron donor eOCH3 at R2 seems to reduce the nonlinear
absorption for electron withdrawing attachment at R1. This
eNO2, and electron donor substitution eOCH3 and eH. In Fig. 5 the
nonlinear absorption coefficient (b) is plotted as a function of the
substituent. It has been shown earlier that the two-photon ab-
sorption cross-section increases with the strength of the acceptor
bridge in a D-p-A-p-D type system and also depends on the sep-
aration between the donor and acceptor at the two ends [44e46].
This separation is decided by the base structure. In our case, since
all the compounds have the same skeleton bridge structure the
observed changes in the nonlinear absorption coefficient have to be
attributed to the effect caused by the substitutions at both ends of

A. Saha et al. / Journal of Molecular Structure 1219 (2020) 128578
7
form and can be clubbed together to give an effective nonlinear
absorption coefficient, . Thus Eqn. (1) would be still applicable.
b
The possible nonlinear absorption processes for the present set
of compounds can be understood with the help of Fig. 6 (a), which
shows the lowest energy levels of S01 and S03. Other compounds
have a similar energy level structure. Based on the energy bands of
the compounds and the photon energy used in the nonlinearity
measurements (532 nm), we propose three major contributions to
the optical nonlinearity of the present compounds. The schematic
of these three processes is given in Fig. 6(b) as P1, P2 and P3. The
first process, P1, is the intrinsic two-photon absorption process. As
can be seen from Fig. 6(b), the
p -
p* transition wavelength lies
close to 266 nm. The presence of a real energy band at the two-
photon energy will lead to a finite contribution to the two-
photon absorption at 532 nm [48,49]. The strength of the two-
photon absorption will depend on the detuning,
d, between the
energy of the
p
-
p* transition and the total energy of two photons,
4.66 eV. The second process P2 is the two-step two-photon ab-
sorption. Due to the large spectral width of the long wavelength
absorption band (Fig. 2) a negligibly small linear absorption may
occur at the input wavelength 532 nm. The strength of this ab-
Fig. 5. The estimated nonlinear absorption coefficient, b, is plotted as a function of
substitution in the chalcone derivatives.
sorption depends on the detuning,
D
between n-p* transition and
the excitation wavelength, the strength of the transition and its
spectral width. This minuscule absorption will excite carriers from
reduction tells that A-
nonlinear absorption coefficient than the corresponding D-
D motif. However, there is a trade off between A- -A- -D and the
electron donor moiety and the terminal acceptor group. The
unsubstituted 9-position of the anthracene derivatives with the
methoxy substituted one was a much more proficient absorber.
Probably the extensive conjugation of the methoxy group with the
p
-A-
p
-D is more effective in increasing the
p-A-
p-
n to
get further excited to even higher energy levels (like
p
*. These carriers can get accumulated in the level p* and can
p
p
s
*) by ab-
sorption of another photon at 532 nm. We also propose a third-
process (P3). The small absorption from n to p* will create empty
states in an otherwise filled n band. Now absorption from a filled
p
band to the vacancies created in the n band can also contribute to
nonlinear absorption process. In addition to the energy of the
transitions, their width and transition strength would all contribute
anthracene
turn decreases the
p
-system exceeds the “conjugation signature” and in
b
value [47].
Now we look at the possible reasons for the higher nonlinear
absorption observed in the compounds under study. In nanosecond
time scales, multiple processes can contribute to the nonlinear
absorption [31]. These include direct two-photon absorption
(which is instantaneous) and two-step two-photon absorption
involving two successive one-photon transitions. The latter can
entail some delay between the two one-photon transitions. It is to
be noted that for a sufficiently long laser pulse all these nonlinear
absorption processes will have intensity dependence of similar
in defining the final nonlinear absorption coefficient of
a
compound.
Electron donating substituents, like eCH3 are known to increase
the -electron conjugation and can also reduce the energy gap [50].
p
In the present case, compounds with eNO2 substitution have the
lowest energy gap (n ꢀ p* transition) reducing the energy differ-
ence D. Such reduction in D can increase the nonlinear absorption
through all the processes P1, P2 and P3. Even among these com-
pounds having eNO2 substitution the S08 has the smallest which
D
also shows the highest nonlinear absorption. We have also per-
formed z-scan measurements at 1064 nm, the fundamental laser
wavelength, and found no measurable nonlinear absorption. When
measured at 1064 nm processes similar to P2 and P3 would not
contribute to the nonlinear absorption. Further the contribution
from P1 will also be weak since there is no energy band near single-
photon (linear) absorption. This observation also confirms the
presented model of nonlinear absorption at 532 nm. Note that for
measurements at 532 nm the compound with the strongest
nonlinear absorption, S03, has a very small linear absorption.
However, any attempt to increase the nonlinear absorption by
further reduction of
D would result in increasing the linear ab-
sorption. Samples having linear absorption loss are in general not
good for nonlinear optical applications.
Densely packing the molecules in crystal form can increase the
overall nonlinear absorption coefficient of the sample. Further,
solid state materials are more suitable for most device applications.
We find that it is possible to prepare single crystals of these com-
pounds (preparation method and crystal details of two of the
compounds are given section-IV of SI). The formation of single
crystals indicates the possibility of using these compounds in solid
state form. Many of the applications, for example two-photon
fluorescence excitation microscopy, two-photon up-conversion
Fig. 6. (a) Schematic of the energy levels in the present set of compounds near the
HOMO-LUMO gap E1. E2 is the second lower energy transition. The vertical upward
green arrows represent a single photon with energy 2.33 eV (532 nm). The numbers
shown are in eV. See the text for the details of
d and D. (b) the proposed three different
processes which can contribute to the measured nonlinear absorption in the
compounds.

8
A. Saha et al. / Journal of Molecular Structure 1219 (2020) 128578
lasing, 3D nano/microfabrications and photodynamic therapy
require molecules with high nonlinear absorption cross-sections.
Many of the chalcone derivatives reported here have these neces-
sary properties making them suitable candidates for such nonlinear
optical applications.
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Declaration of competing interest
The authors declare that they have no known competing
financial interests or personal relationships that could have
appeared to influence the work reported in this paper.
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A. S. would like to thank DST, INSPIRE Fellowship New Delhi,
Government of India for award of research fellowship, Dept. of Instr.
& USIC, Gauhati University, Assam, India for providing the single
crystal XRD data, R. K. Laha of CBMR, Lucknow and D. Sar of I.I.T
Guwahati for their assistance and V. Shukla for his help during z-
scan experiments.
Appendix A. Supplementary data
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