Design, synthesis, characterization and fluorescence property evaluation of dehydroacetic acid-based chalcones

Article abstract of DOI:10.1007/s13738-019-01839-4

Abstract: In this study, we decided to synthesize some new chalcone-type dyes derived from dehydroacetic acid (DHA) by the condensation of 4-amino-substituted benzaldehyde with DHA under the base-catalyzed condition and investigate their ability for rearrangement in acidic condition. For this purpose, initially we prepared the 4-aminobenzaldehyde derivatives via nucleophilic aromatic substitution reaction of 4-fluorobenzaldehyde with variety of amines in the presence of K₂CO₃ as base in DMF. The Knoevenagel condensation of DHA with 4-aminobenzaldehyde derivatives results in the desired compounds. In continuation, Fries rearrangement applied on DHA-chalcone compounds results in characterization of new pyranilidene-type derivatives. The optical responses of new dyes containing UV–Vis absorption and fluorescence spectroscopy were measured in dichloromethane (ET = 40?kcal/mol). Pyranilidene derivatives show low λ_max values in comparison with chalcones, and molecule with strong dipole, in polar solvents, shows the bathochromic shift due to more stabilization of excited state in compared with ground state of molecule. Large stocks shifts were obtained for synthesized compounds. Graphic abstract: [Figure not available: see fulltext.].

Full text of DOI:10.1007/s13738-019-01839-4

Journal of the Iranian Chemical Society
https://doi.org/10.1007/s13738-019-01839-4
ORIGINAL PAPER
Design, synthesis, characterization and fuorescence property
evaluation of dehydroacetic acid‑based chalcones
Reza Teimuri‑Mofrad1 · Keshvar Rahimpour1 · Mohammad Gholizadeh1
Received: 21 October 2019 / Accepted: 16 December 2019
© Iranian Chemical Society 2019
Abstract
In this study, we decided to synthesize some new chalcone-type dyes derived from dehydroacetic acid (DHA) by the conden-
sation of 4-amino-substituted benzaldehyde with DHA under the base-catalyzed condition and investigate their ability for
rearrangement in acidic condition. For this purpose, initially we prepared the 4-aminobenzaldehyde derivatives via nucleo-
philic aromatic substitution reaction of 4-fuorobenzaldehyde with variety of amines in the presence of K2CO3 as base in
DMF. The Knoevenagel condensation of DHA with 4-aminobenzaldehyde derivatives results in the desired compounds. In
continuation, Fries rearrangement applied on DHA-chalcone compounds results in characterization of new pyranilidene-type
derivatives. The optical responses of new dyes containing UV–Vis absorption and fuorescence spectroscopy were measured
in dichloromethane (ET=40 kcal/mol). Pyranilidene derivatives show low λmax values in comparison with chalcones, and
molecule with strong dipole, in polar solvents, shows the bathochromic shift due to more stabilization of excited state in
compared with ground state of molecule. Large stocks shifts were obtained for synthesized compounds.
Graphic abstract
Keywords Dehydroacetic acid · Chalcone · 4-Amino-substituted benzaldehyde · Pyran
Introduction
The heterocyclic compounds, particularly oxygen-containing
heterocycles, are challenging models for a large number of
usages in organic chemistry. 3-Acetyl-4-hydroxy-6-methyl-
* Reza Teimuri-Mofrad
2H-pyran-2-one is one of the important oxygen-containing
heterocyclic compounds; it is commonly known as dehy-
droacetic acid (DHA). DHA and the products derived from
it found wide application in various physiological and
teimuri@yahoo.com; teymouri@tabrizu.ac.ir
1
Department of Organic and Biochemistry, Faculty
of Chemistry, University of Tabriz, Tabriz, Iran
Vol.:(0123456789)
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Journal of the Iranian Chemical Society
synthetic areas as well as pharmaceutical, cosmetic and food
industries [1–3].
spectra were recorded at 25 °C using CDCl3 as solvent,
with chemical shifts measured in ppm and referenced to
the residual solvent as follows: CHCl3 = 7.26 ppm (1H),
76.0 ppm (13C). FT-IR spectral data are reported as wave
numbers (cm−1). Elemental analyses were carried out with
an Elementar Vario EL III instrument. The mass spectra are
operated at 70 eV by Agilent (5975C VL) instrument; the
most important peaks are reported in m/z units with M+ as
the molecular ion and with the corresponding intensities in
%. The electronic absorption spectra were obtained using
SPECORD 250 Analytik Jena UV/Vis spectrophotometer;
fuorescence emission spectra were measured on an Edin-
burgh FLS 920 fuorometer (UK). Melting points were deter-
mined on a MEL-TEMP model 1202D and are uncorrected.
DHA with four active sites is a susceptible molecule for
nucleophilic and electrophilic reactions. DHA can react with
diferent aldehydes and produce variety of chalcones [4, 5].
The chalcones are important conjugated systems which
are used as intermediates to synthesize various applicable
derivatives. Representative examples of natural structures
with chalcone units are illustrated in Fig. 1.
Conjugated systems are potential privileged compounds
that have been known due to their excellent photo-physical
and optical properties. These type compounds have been
vastly explored in lasers, fuorogenic probes, pigments, solar
cells, nonlinear optical materials, etc. [6–8].
Outstanding feature of DHA and its derivatives is their
ability to rearrangement to 4H-pyran-4-one derivatives.
Research work in our laboratory has been recently con-
cerned with the reaction of 4H-pyran derivatives with vari-
ous aromatic aldehydes in order to conjugated compounds
with modifed optical properties [9–12]. In this research,
we report the synthesis of some new chalcone derivatives
with DHA core via Knoevenagel condensation of DHA with
amine-substituted aldehydes, followed by rearrangement to
4H-pyran derivatives. In addition, their UV–Vis absorption
and fuorescence emission properties were studied.
General procedure for the synthesis
of 4‑amino‑substituted benzaldehyde (3a–e)
A mixture of 4-fuorobenzaldehyde (1) (0.25 g, 2 mmol),
appropriate amines (2a–e) (3 mmol) and anhydrous potas-
sium carbonate (0.4 g) was stirred in DMF (5 mL) for 24 h at
80 °C. The mixture was concentrated under low pressure and
left to cool. The mixture was then poured into ice water and
left overnight. The formed solid was fltered, washed with
water and crystallized with methanol to yield compounds
3a–e [13].
Experimental
General procedure for the synthesis of chalcone
DHA derivatives (5a–e)
General
In a round bottom flask equipped with a magnetic stir
bar, refux condenser and a Soxhlet condenser flled with
molecular sieves, DHA (4, 0.168 g, 1 mmol), 1 mmol of
appropriate amino benzaldehyde 3a–e and catalytic amount
of piperidine (8.5 mg, 0.1 mmol) were refuxed in dry tolu-
ene for 24 h. After complete reaction, toluene was removed
under reduced pressure and residue was dissolved in CH2Cl2
and washed with water. Combined organic layer was dried
over the anhydrous Na2SO4, and the solvent was removed in
atmospheric pressure. Obtained crude solid was purifed by
recrystallization from EtOH.
Commercial compounds were used without further puri-
fication. Column chromatography was performed using
SiO2 (60 Å, 230–400 mesh, particle size 0.040–0.063 mm)
1
at 25 °C. H NMR (400 MHz) and 13C NMR (100 MHz)
3‑[3‑(4‑Dimethylamino)acryloyl]‑4‑hydroxy‑6‑methyl‑2H‑
pyran‑2‑one (5a)
Using 0.149 g of 4-(dimethylamino)benzaldehyde, 0.268 g
(0.89 mmol) of orange solid was obtained in 89% yield.
m.p: 220–222 °C; FT-IR (KBr, cm−1): 3447 (–OH), 2924
(Aromatic, –CH), 2854 (Aliphatic, –CH), 1695 (C=O), 1241
(C–N); 1H NMR (400 MHz, CDCl3, 300 K): δ [ppm]=18.36
(s, 1H, OH), 8.18–8.14 (dd, 1H, J=16 Hz, =CH), 7.99–7.95
(dd, 1H, J=16 Hz, =CH), 7.67–7.64 (d, 2H, J=12 Hz, Ar),
6.99–6.96 (d, 2H, J=12 Hz, Ar), 5.93 (s, 1H, Pyran), 2.66 (s,
Fig. 1 Representative examples of chalcone units in natural structures
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Journal of the Iranian Chemical Society
3H, –CH3), 2.27–2.26 (s, 6H, N-CH3); 13C NMR (100 MHz,
CDCl3, 300 K): δ [ppm]=183.70, 174.50, 165.42, 165.05,
149.70, 141.27, 128.94, 125.63, 125.42, 111.30, 103.40,
102.14, 46.75, 20.83; MS (70 eV): m/z (%): 299.12 (100)
[M+]. Elemental analysis: calcd. for C17H17NO4 (%): C
68.22, H 5.72, N 4.68; found (%): C 67.93, H 5.71, N 4.69.
δ [ppm]=18.43 (s, 1H, OH), 8.17–8.13 (dd, 1H, J=16 Hz,
=CH), 7.98–7.94 (dd, 1H, J =16 Hz, =CH),7.62–7.60 (d,
2H, J = 8 Hz, Ar), 6.89–6.87 (d, 2H, J = 8 Hz, Ar), 5.92
(s, 1H, Pyran), 3.41–3.37 (3, 4H, N-CH2), 2.59–2.58 (3,
4H, N-CH2), 2.37 (s, 3H, N-CH3), 2.25 (s, 3H, –CH3); 13
C
NMR (100 MHz, CDCl3, 300 K): δ [ppm]=183.08, 174.83,
166.33, 164.50, 142.23, 129.15, 125.87, 124.32, 113.33,
104.44, 102.10, 54.83, 46.60, 25.50, 20.58; MS (70 eV):
m/z (%): 354.16 (100) [M+]. Elemental analysis: calcd. for
C20H22N2O4 (%): C 67.78, H 6.26, N 7.90; found (%): C
67.75, H 6.27, N 7.91.
3‑[3‑(4‑Pyrrolidino)acryloyl]‑4‑hydroxy‑6‑methyl‑2H‑
pyran‑2‑one (5b)
Using 0.175 g of 4-(pyrrolidino)benzaldehyde, 0.313 g
(0.96 mmol) of brown solid was obtained in 96% yield.
m.p: 174–176 °C; FT-IR (KBr, cm−1): 3450 (–OH), 3114
(Aromatic, –CH), 2923 (Aliphatic, –CH), 1696 (C=O), 1324
(C–N); 1H NMR (400 MHz, CDCl3, 300 K): δ [ppm]=18.71
(s, 1H, OH), 8.11–8.07 (dd, 1H, J=16 Hz, =CH), 8.03–7.99
(dd, 1H, J = 16 Hz, =CH), 7.61–7.59 (d, 2H, J = 12 Hz,
Ar), 6.57–6.54 (d, 2H, J= 8 Hz, Ar), 5.90 (s, 1H, Pyran),
3.40–3.37 (t, 4H, N-CH2), 2.24 (s, 3H, –CH3), 2.06–2.02
(m, 4H, –CH2); 13C NMR (100 MHz, CDCl3, 300 K): δ
[ppm] = 189.98, 183.00, 166.17, 149.27, 147.68, 141.20,
131.06, 125.18, 121.38, 114.63, 111.00, 102.28, 46.75,
24.40, 19.47; MS (70 eV): m/z (%): 325.13 (100) [M+].
Elemental analysis: calcd. for C19H19NO4 (%): C 70.14, H
5.89, N 4.31; found (%): C 70.08, H 5.88, N 4.32.
3‑[3‑(4‑Morpholino)acryloyl]‑4‑hydroxy‑6‑methyl‑
2H‑pyran‑2‑one (5e)
Using 0.191 g of 4-(morpholino)benzaldehyde, 0.296 g
(0.87 mmol) of dark brown orange was obtained in 87%
yield. m.p: 241–242 °C; FT-IR (KBr, cm−1): 3448 (–OH),
3115 (Aromatic, –CH), 2924 (Aliphatic, –CH), 1712
(C=O), 1264 (C–N); 1H NMR (400 MHz, CDCl3, 300 K):
δ [ppm]=18.33 (s, 1H, OH), 8.20–8.16 (dd, 1H, J=16 Hz,
=CH), 7.98–7.94 (dd, 1H, J=16 Hz, =CH), 7.65–7.63 (d,
2H, J = 8 Hz, Ar), 6.98–6.96 (d, 2H, J = 8 Hz, Ar), 5.94
(s, 1H, Pyran), 3.90 (t, 4H, CH2), 3.32 (t, 4H, –CH2), 2.27
(s, 3H, –CH3); 13C NMR (100 MHz, CDCl3, 300 K): δ
[ppm] = 180.24, 170.28, 165.48, 160.35, 147.68, 125.57,
125.20, 123.25, 110.45, 103.17, 101.10, 65.30, 46.75, 18.70;
MS (70 eV): m/z (%): 341.13 (100) [M+]. Elemental analy-
sis: calcd. for C19H19NO5 (%): C 66.85, H 5.61, N 4.10;
found (%): C 66.83, H 6.62, N 4.11.
3‑[3‑(4‑Piperidino)acryloyl]‑4‑hydroxy‑6‑methyl‑2H‑pyran‑
2‑one (5c)
Using 0.189 g of 4-(piperidino)benzaldehyde, 0.308 g
(0.91 mmol) of dark brown solid was obtained in 91%
yield. m.p: 178–180 °C; FT-IR (KBr, cm−1): 3415 (–OH),
3086 (Aromatic, –CH), 2931 (Aliphatic, –CH), 1711
(C=O), 1236 (C–N); 1H NMR (400 MHz, CDCl3, 300 K):
δ [ppm]=18.57 (s, 1H, OH), 8.15–8.11 (dd, 1H, J=16 Hz,
=CH), 7.99–7.95 (dd, 1H, J=16 Hz, =CH), 7.60–7.58 (d,
2H, J=8 Hz, Ar), 6.87–6.85 (d, 2H, J=8 Hz, Ar), 5.91 (s,
1H, Pyran), 3.38–3.37 (t, 4H, N-CH2), 2.24 (s, 3H, –CH3),
1.69 (m, 6H, –CH2); 13C NMR (100 MHz, CDCl3, 300 K):
δ [ppm]=188.61, 179.61, 165.88, 147.36, 146.95, 141.51,
129.15, 123.45, 115.75, 113.15, 101.35, 99.50, 45.88, 23.53,
19.70, 13.24; MS (70 eV): m/z (%): 339.15 (100) [M+]. Ele-
mental analysis: calcd. for C20H21NO4 (%): C 70.78, H 6.24,
N 4.13; found (%): C 70.75, H 6.25, N 4.14.
General procedure for the Fries rearrangement
A mixture of 1 mmol chalcone DHA derivatives 5a–e in
acetic acid (5 mL) and concentrated hydrochloric acid
(5 mL) was heated at 110 °C for 5 h. To cold reaction
mixture, 5 mL of distilled water was added and decom-
posed with cold sodium hydroxide solution (10%).
Obtained solid was filtered and washed with water. The
crude products were purified by recrystallization from
EtOH.
2‑[(4‑(Dimethylamino)styryl]‑6‑methyl‑4H‑pyran‑4‑one (6a)
Using 0.299 g of 5a, 0.234 g (0.92 mmol) of orange solid
was obtained in 92% yield. m.p: 185–187 °C; FT-IR (KBr,
cm−1): 3062 (Aromatic, –CH), 2960 (Aliphatic, –CH), 1704
3‑[3‑(N‑Methylpiperazino)acryloyl]‑4‑hydroxy‑6‑methyl‑2H‑
pyran‑2‑one (5d)
1
(C=O), 1233 (C–N), 1118 (C–O); H NMR (400 MHz,
Using 0.204 g of 4-(N-methylpiperazino)benzaldehyde,
0.336 g (0.95 mmol) of dark brown solid was obtained in
95% yield. m.p: 195–197 °C; FT-IR (KBr, cm−1): 3407
(–OH), 2933 (Aromatic, –CH), 2854 (Aliphatic, –CH), 1698
(C=O), 1243 (C–N); 1H NMR (400 MHz, CDCl3, 300 K):
CDCl3, 300 K): δ [ppm]=7.57–7.53 (d, 2H, J=8 Hz, Ar),
7.32–7.28 (dd, 1H, J = 16 Hz, =CH), 6.95–6.93 (d, 2H,
J = 8 Hz, Ar), 6.84–6.80 (dd, 1H, J = 16 Hz, =CH), 6.17
(s, 1H, Pyran), 6.10 (s, 1H, Pyran), 3.26 (s, 6H, N-CH3),
2.26 (s, 3H, –CH3); 13C NMR (100 MHz, CDCl3, 300 K):
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Journal of the Iranian Chemical Society
δ [ppm]=188.29, 167.16, 162.77, 152.82, 137.27, 127.70,
123.27, 117.52, 114.32, 112.71, 110.32, 40.12, 19.27; MS
(70 eV): m/z (%): 255.13 (100) [M+]. Elemental analysis:
calcd. for C16H17NO2 (%): C 75.27, H 6.71, N 5.49; found
(%): C 75.25, H 6.72, N 5.50.
CDCl3, 300 K): δ [ppm]=181.30, 167.16, 162.58, 152.80,
134.15, 126.90, 114.40, 114.33, 113.32, 111.30, 47.43,
40.12, 39.91, 18.79; MS (70 eV): m/z (%): 310.17 (100)
[M+]. Elemental analysis: calcd. for C19H22N2O2 (%): C
73.52, H 7.14, N 9.03; found (%): C 73.55, H 7.15, N 9.02.
2‑[4‑(Pyrrolidin‑1‑yl)styryl]‑6‑methyl‑4H‑pyran‑4‑one (6b)
2‑[4‑(Morpholino)styryl]‑6‑methyl‑4H‑pyran‑4‑one (6e)
Using 0.325 g of 5b, 0.247 g (0.88 mmol) of light orange
solid was obtained in 88% yield. m.p: 126–128 °C; FT-IR
(KBr, cm−1): 3112 (Aromatic, –CH), 2923 (Aliphatic, –CH),
1652 (C=O), 1271 (C–N), 1031 (C–O); 1H NMR (400 MHz,
CDCl3, 300 K): δ [ppm]=7.74–7.71 (d, 2H, J=8 Hz, Ar),
7.36–7.32 (dd, 1H, J = 16 Hz, =CH), 6.96–6.94 (d, 2H,
J = 8 Hz, Ar), 6.90–6.86 (dd, 1H, J = 16 Hz, =CH), 6.22
(s, 1H, Pyran), 6.17 (s, 1H, Pyran), 3.42–3.20 (t, 4H,
N-CH2), 2.45–2.42 (m, 4H, –CH2), 2.25 (s, 3H, CH3);
13C NMR (100 MHz, CDCl3, 300 K): δ [ppm] = 187.20,
168.50, 162.65, 152.70, 132.45, 130.23, 125.68, 120.12,
114.40, 112.28, 95.87, 53.80, 23.50, 20.49; MS (70 eV):
m/z (%): 281.14 (100) [M+]. Elemental analysis: calcd. for
C18H19NO2 (%): C 76.84, H 6.81, N 4.98; found (%): C
76.86, H 6.80, N 4.99.
Using 0.341 g of 5e, 0.285 g (0.96 mmol) of light orange
solid was obtained in 96% yield. m.p: 192–194 °C; FT-IR
(KBr, cm−1): 3046 (Aromatic, –CH), 2953 (Aliphatic, –CH),
1706 (C=O), 1232 (C–N), 1116 (C–O); 1H NMR (400 MHz,
CDCl3, 300 K): δ [ppm]=7.54–7.51 (d, 2H, J=8 Hz, Ar),
7.34–7.30 (dd, 1H, J = 16 Hz, =CH), 6.98–6.96 (d, 2H,
J=8 Hz, Ar), 6.86–6.84 (dd, 1H, J=16 Hz, =CH), 6.19 (s,
1H, Pyran), 6.07 (s, 1H, Pyran), 3.72 (t, 4H, N-CH2), 3.20
(t, 4H, O-CH2), 2.30 (s, 3H, CH3); 13C NMR (100 MHz,
CDCl3, 300 K): δ [ppm]=178.89, 165.16, 162.30, 151.80,
135.07, 128.90, 125.33, 116.02, 114.40, 113.32, 111.70,
65.96, 47.43, 19.27; MS (70 eV): m/z (%): 297.14 (100)
[M+]. Elemental analysis: calcd. for C18H19NO3 (%): C
72.71, H 6.44, N 4.71; found (%): C 77.73, H 6.43, N 4.72.
2‑[(4‑(Piperidin‑1‑yl)styryl]‑6‑methyl‑4H‑pyran‑4‑one (6c)
Result and discussion
Using 0.339 g of 5c, 0.250 g (0.85 mmol) of brown solid
was obtained in 85% yield. m.p: 135–139 °C; FT-IR (KBr,
cm−1): 3086 (Aromatic, –CH), 2960 (Aliphatic, –CH), 1711
Chalcone derivatives are attractive candidates for linear and
nonlinear optical applications. These types of compounds
fnd unique potential for use in wide range of practical optic
felds. Various methods were reported for preparation of
chalcones in the literature. The most convenient procedure
is involving the base-mediated condensation of aryl alde-
hyde with aryl methyl ketone. In order to preparation of
DHA-based chalcones, we used Knoevenagel condensation
of dehydroacetic acid as methyl ketone with 4-amino-substi-
tuted benzaldehyde. Firstly, benzaldehyde derivatives were
prepared via nucleophilic aromatic substitution of secondary
amines with 4-fuorobenzaldehyde in DMF and K2CO3 was
employed as the base for the coupling reaction [13].
1
(C=O), 1236 (C–N), 1120 (C–O); H NMR (400 MHz,
CDCl3, 300 K): δ [ppm]=7.43–7.41 (d, 2H, J=8 Hz, Ar),
7.31–7.27 (dd, 1H, J = 16 Hz, =CH), 6.98–6.96 (d, 2H,
J=8 Hz, Ar), 6.51–6.47 (dd, 1H, J=16 Hz, =CH), 6.14 (s,
1H, Pyran), 6.07 (s, 1H, Pyran), 3.28 (t, 4H, N-CH2), 2.32 (s,
3H, CH3), 1.71–1.63 (m, 6H, –CH2),; 13C NMR (100 MHz,
CDCl3, 300 K): δ [ppm]=179.30, 165.10, 162.30, 155.80,
137.07, 126.90, 126.33, 116.02, 114.48, 114.35, 111.70,
47.05, 38.07, 20.43, 18.72; MS (70 eV): m/z (%): 295.16
(100) [M+]. Elemental analysis: calcd. for C19H21NO2 (%):
C 77.26, H 7.17, N 4.74; found (%): C 77.24, H 7.16, N 4.75.
Obtained aldehydes were reacted with DHA under Kno-
evenagel condensation reaction condition (Scheme 1). As
results that are obtained from experiments, dry toluene was
chosen as solvent because we need higher temperature to
complete the reaction. In the mild temperature which can
be supplied with aldol condensation routine alcoholic sol-
vents such as methanol and ethanol, the reaction was not
complete. In addition, we used Soxhlet extractor flled with
4oA molecular sieves to remove the produced water during
the reaction. Catalytic amount of piperidine was efective in
progression of the reaction. In the literature, 5a and 5e were
synthesized via complexion of DHA with BF3 to increase
the reactivity of 3-position acetyl group toward aldehydes,
and hydrolysis of obtained complex in fnal step [14, 15]. In
2‑[4‑(N‑methylpiperazine‑1‑yl)styryl]‑6‑methyl‑4H‑pyran‑4‑
one (6d)
Using 0.354 g of 5d, 0.257 g (0.83 mmol) of yellow solid
was obtained in 83% yield. m.p: 152–154 °C; FT-IR (KBr,
cm−1): 3039 (Aromatic, –CH), 2930 (Aliphatic, –CH), 1655
1
(C=O), 1242 (C–N), 1150 (C–O); H NMR (400 MHz,
CDCl3, 300 K): δ [ppm]=7.43–7.41 (d, 2H, J=8 Hz, Ar),
7.30–7.26 (dd, 1H, J = 16 Hz, =CH), 6.89–6.87 (d, 2H,
J=8 Hz, Ar), 6.50–6.46 (dd, 1H, J=16 Hz, =CH), 6.14 (s,
1H, Pyran), 6.05 (s, 1H, Pyran), 3.33 (t, 4H, N-CH2), 2.69
(t, 4H, N-CH2), 2.30 (s, 3H, CH3); 13C NMR (100 MHz,
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Journal of the Iranian Chemical Society
Scheme 1 Synthesis of chal-
cone DHA derivatives (5a–e)
and Fries rearrangement on
them
comparison, our method is preferred due to less number of
reaction steps and afordable used materials.
molecular structures of the synthesized compounds were
1
confrmed by FT-IR, H NMR, 13C NMR and mass spec-
In continuation, we examined the Fries rearrangement in
acidic condition for synthesized chalcone derivatives. Using
acetic acid and hydrochloric acid in 100 °C for 8 h gives
us the pyranilidene derivatives of relevant aldehydes. All
troscopies and elemental analysis. Figure 2 depicts the 1H
NMR spectra of 5c and 6c as representative of chalcone
derivative and its rearrangement products. Disappear of
the largest chemical shift belongs to the alcoholic proton of
Fig. 2 1H NMR spectra of 5c and 6c as representative of chalcone derivatives and its rearrangement products
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Journal of the Iranian Chemical Society
DHA in 1H NMR spectra of 6c is a confrmation that Fries
rearrangement was performed.
378–442 for pyranilidene-based compounds. The related
descriptions are presented in Table 1.
Doublet signals in 7–8 ppm with coupling constant of
16 Hz in 1H NMR spectra of 5c related to exocyclic acrylic
protons corresponding to all-trans geometry for synthesized
chalcones and during Fries rearrangement, this geometry
remains intact.
Comparison between compounds series 5 and 6 shows
the larger λmax value for chalcone derivatives (5a–e) which
exhibited smaller transition energies. We know compounds 5
and 6 shared same donor groups; thus, their transition ener-
gies can depend on molecular structure of chromophores.
Dichloromethane is a polar solvent with ET=40 kcal/mol;
it is obvious that a molecule with strong dipole, in polar
solvents, shows the bathochromic shift due to more stabili-
zation of excited state in comparison with ground state of
molecule. This phenomenon is in agreement with decrease
in the transition energy.
To evaluate the optical properties of synthesized com-
pounds, we measured the electronic absorption and fuores-
cence spectra of chalcone and pyranilidene derivatives in
dichloromethane. As can be seen from Fig. 3, the absorption
spectra of target compounds exhibit a strong π–π* transi-
tion in the range of 443–491 for chalcone derivatives and
Fig. 3 Absorption (a, b) and fuorescence (c, d) spectra of 5(a–e) and 6(a–e)
Table 1 Fluorescent and UV–
Vis parameters of products 5a–e
and 6a–e
Entry
λmax (nm)
λem (nm)
∆νa (cm−1
)
Entry
λmax (nm)
λem (nm)
∆νa (cm−1
)
5a
5b
5c
5d
5d
475
491
465
453
443
580
580
590
580
580
3811
3125
4556
4833
5331
6a
6b
6c
6d
6e
402
387
388
378
442
440
470
520
440
450
2148
4563
6542
3727
402
aStokes shift
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Journal of the Iranian Chemical Society
new class of chalcones. These products have been success-
fully rearranged to pyran derivatives via Fries reaction. Opti-
cal properties of all synthesized compounds were studied
using UV–Vis and fuorescence spectroscopy.
Acknowledgements The authors would like to acknowledge the fnan-
cial support from University of Tabriz.
Fig. 4 Fluorescence emission photographs of synthesized compounds
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