Green-synthesis, characterization, photostability and polarity studies of novel Schiff base dyes using spectroscopic methods

Article abstract of DOI:10.1134/S1068162012050056

Preparation, characterization, photostability and polarity studies of novel Schiff base dyes using spectroscopic methods were achieved. The Schiff base dyes were prepared by the reaction of salicylaldehyde/2-hydroxy-l-naphthaldehyde with aminophenazone un

Full text of DOI:10.1134/S1068162012050056

ISSN 1068ꢀ1620, Russian Journal of Bioorganic Chemistry, 2012, Vol. 38, No. 5, pp. 533–538. © Pleiades Publishing, Ltd., 2012.
GreenꢀSynthesis, Characterization, Photostability and Polarity
Studies of Novel Schiff Base Dyes Using Spectroscopic Methods1
2
Hadi M. Marwania, b, Abdullah M. Asiria, b, and Salman A. Khana,
a Department of Chemistry, Faculty of Science, King Abdulaziz University, P.O. Box 80203, Jeddah, 21589 Saudi Arabia
b Center of Excellence for Advanced Materials Research, King Abdulaziz University,
P.O. Box 80203, Jeddah, 21589 Saudi Arabia
Received October 18, 2011; in final form, December 23, 2011
Abstract—Preparation, characterization, photostability and polarity studies of novel Schiff base dyes using
spectroscopic methods were achieved. The Schiff base dyes were prepared by the reaction of salicylaldeꢀ
hyde/2ꢀhydroxyꢀlꢀnaphthaldehyde with aminophenazone under microwave irradiation. The spectroscopic
(FTꢀIR, 1H NMR, 13C NMR, Mass) studies and elemental analyses were in good agreement with chemical
structure of synthesized compounds. In addition, UVꢀVis and fluorescence spectroscopic experiments
showed that these dyes are good absorbent and fluorescent. Based on the photostability study of these dyes,
minimal to no loss in fluorescence intensities of 4ꢀ[(2ꢀhydroxyꢀbenzylidene)ꢀamino]1,5ꢀdimemylꢀ2ꢀpheꢀ
nylꢀ1,2ꢀdihydroꢀpyrazolꢀ3ꢀone (D1) (6.14%) and 4ꢀ[(2ꢀhydroxyꢀnaphthalenꢀlꢀylmethylene)ꢀamino]ꢀ1,5ꢀ
dimethylꢀ2ꢀphenylꢀ1,2ꢀdihydroꢀpyrazolꢀ3ꢀone (D2) (2.95%) was observed with an increase in the exposure
time using timeꢀbased fluorescence steadyꢀstate experiments. These studies also inferred that these Schiff
base dyes have a high photostability against photobleaching. In addition, Dye
2 is found to be more sensitive
than Dye to the polarity of the microenvironment provided by different solvents based on the results of fluoꢀ
1
rescence polarity studies.
Keywords: Schiff bases, pyrazolꢀ3ꢀone, florescent, photostability
DOI: 10.1134/S1068162012050056
2 1
INTRODUCTION
development of coordination chemistry as a whole.
However, it was not until the 1950s that concrete and
rapid advances in this field became evident. In early
days, the main efforts were focused on synthesis and
characterization rather than fundamental complexes
[14].
The application of donor accepter azomethane
(HC=N) dyes in science and technology is wellꢀ
known and wellꢀdocumented [1, 2]. Azomethane
derivatives are coloring magnets and have excellent
thermal and optical properties. In addition, these molꢀ
ecules have numerous applications such as the optical
data storage [3], photoswitching [4], nonꢀlinear optics
[5], photochromic materials [1], dyes [6], and chemiꢀ
cal analysis [7]. On the other hand, wide spectrum of
biological activities are associated with these moleꢀ
cules, such as antimicrobial [8], antifungal [9], antituꢀ
mor [10], herbicide [11], inhibition of DNA, RNA,
and protein synthesis, nitrogen fixation, and carcinoꢀ
genesis [12]. Furthermore, in the past decade the
highꢀdensity optical data storage has been a subject of
an extensive research. In general, azomethane dyes,
phthalocyanine dyes, and metal–azo complex dyes
are used in the recording layer of DVDꢀR (Digital Verꢀ
satile DiscꢀRecordable) discs [13]. They are usually
synthesized by the coupling reaction of an aldehyde
with primary amine. Metal complexes derived from
Schiff bases, have played an important part in the
Heterocyclic azomethane compounds are extenꢀ
sively used as metal complexing ligands in spectrophoꢀ
tometry, chromatography and electrophoresis studies
since they can advantageously form highly sensitive
metal complexes and are easily synthesized and puriꢀ
fied [15]. 2ꢀHydroxy Schiff base ligands are of interest
mainly due to the existence of (O–H···N and N–
H···O) type hydrogen bonds and tautomerism between
enolꢀimine and ketoꢀenamine forms (Scheme). In
addition, several 2ꢀhydroxy Schiff bases, being relaꢀ
tively simple in structure and exhibiting intramolecuꢀ
lar proton transfer, have attracted considerable attenꢀ
tion from both experimental and theoretical points of
view [16–20]. The quantum yield of these 2ꢀhydroxy
Schiff bases is also found to increase with an increase
in the solvent viscosity. In accordance, this study
reports the synthesis of novel Schiff bases and their
spectroscopic properties. Moreover, the effect of phoꢀ
tobleaching on the photostability of these Schiff bases
was investigated by use of timeꢀbased fluorescence
steadyꢀstate measurements. The sensitivity of new
1
The article is published in the original.
Corresponding author: fax: +966
sahmad_phd@yahoo.co.in.
2
2 6952292; eꢀmail:
533

534
MARWANI et al.
The synthetic route is outlined in Scheme. The FTIR
spectra of Schiff bases of pyrazolꢀ3ꢀone (D1 and D2
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
)
D1
D2
showed absorption bands at 2935 and 2956 cm–1 for
aromatic C–H and at 1448 and 1479 cm–1 for azomeꢀ
thine group (–CH=N–). The absence of the absorpꢀ
tion band at 1700–1750 cm–1 also confirms the conꢀ
version of –CHO group to –CH=N– group. The 1H
NMR spectra of hydrazones, as presented in experiꢀ
mental section, showed peaks of aromatic, methyl, and
olefinic (–N=CH–) proton as singlets. The 1H NMR
spectra of Dyes (D1 and D2) showed sharp singlet at
δ
9.84 and 10.85, confirming the presence of azomeꢀ
thine (–CH=N–) proton. The sharp singlet at 3.24
δ
250
300
350 400
Wavelength, nm
450
500
and 3.20 corresponds to the presence of –CH3 group
attached to the nitrogen, and the sharp singlet at 2.42
and 2.46 indicates the –CH3 group attached to the
Fig. 1. UVꢀVis absorption spectra of 10 µM D1 and D2 in
ACN.
carbon. The appearance of multiplets at
was due to aromatic protons.
δ
6.96–8.26
Moreover, 13C NMR spectra showed the signals in
the range of 119.10 and 116.20 ppm and at 134.0
and 134.25 ppm due to aryl carbon and azomethine
carbon, respectively. In the EI mass spectrum, a peak
synthesized Schiff bases toward the polarity of the
microenvironment provided by different solvents was
also examined by fluorescence polarity studies.
δ
δ
appeared at
having molecular formula (C18H17N3O2). In the mass
spectrum of Dye D2 , a peak was observed at
359 ( +1, 100%), which is in consistency with its
molecular formula C22H19N3O2. FTꢀIR, H NMR,
13C NMR spectral data and elemental analysis results
are in agreement with the chemical structures of the
dyes synthesized in this study. In addition, synthesized
D1 and D2 are found to be pure from data obtained by
the elemental analysis, previously given in the syntheꢀ
sis procedures of the experimental section.
m/z 309 (M +1, 100%), for Dye 1 (D1)
OH
H2N
2
(
)
m/z
M
1
OH
N
N
2 min
MW
O
N
+
N
CHO
O
N
D1
Spectroscopic Evaluation of Dyes
UVꢀVis absorption study. UVꢀVis absorption meaꢀ
surements of dyes were performed at the same experiꢀ
mental and instrumental conditions. In general, broad
absorption spectra of D1 and D2 were noticed (Fig. 1).
Figure 1, however, shows different spectral profiles of
D1 and D2. Three characteristic broad bands were
observed in the UVꢀVis absorption spectrum of D2 in
comparison to single broad band of D1, as shown in
Fig. 1. These three broad bands of D2 are centered at
310, 360, and 390 nm. From Fig. 1, it also appears that
D2 is slightly dimmer than D1. This may be attributed
to the distinctive structural composition of the dyes.
H2N
O
HO
N
N
2 min
MW
CHO
N
+
O
N
OH
N
D2
Scheme. Synthetic route of dyes (D1 and D2).
Steadyꢀstate fluorescence spectroscopic study. All
dyes synthesized in this study fluoresced in the acetoꢀ
nitrile and were excited at 360 nm. In general, high
background fluorescence and similar spectral profiles
were observed in the emission spectra of D1 and D2
RESULTS AND DISCUSSION
Chemistry
Schiff base derivatives (D1 and D2) were prepared (Fig. 2). However, it can be noticed that there is a blue
by the reaction of 4ꢀaminophenazone with the correꢀ shift in the emission spectrum of D2 as compared to
sponding active aldehydes by the microwave irradiaꢀ that of D1, displayed in Figs. 2a and 2b). In addition,
tion method described previously in the literature [21]. Fig. 2b indicates that D2 is slightly dimmer than D1
.
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GREENꢀSYNTHESIS, CHARACTERIZATION, PHOTOSTABILITY AND POLARITY STUDIES
535
These results are in good agreement with those
obtained from UVꢀVis absorption study.
(а)
Photostability study. The photostability study of all
dyes was investigated using timeꢀbased fluorescence
measurements. The excitation and emission bandpass
set was at 15 and 5 nm, respectively, and both dyes have
been exposed to the maximum amount of radiation for
30 min in order to induce the photobleaching. Figures 2b
and 3 clearly show the behavior of these two dyes in
terms of their susceptibility to photobleaching. The
progress of photobleaching for D1 and D2 over a
30 min time span is illustrated in Fig. 3. It can be conꢀ
ducted that the intensities of D1 and D2 show minimal
to no loss with an increase in the exposure time. The
intensity of D1, however, decreased by approximately
6.14% after exposure to radiation as compared to that
of D2 (2.95%). These results suggest that these dyes
have very high stability against photobleaching.
D1
D2
420 440 460 480 500 520 540 560 580 600 620
Wavelength, nm
(b)
D1 before photobleaching
D1 after photobleaching
D2 before photobleaching
D2 after photobleaching
Polarity study. Polarity plays a major role in many
chemical, physical, biochemical and biological pheꢀ
nomena. In this study, 10 uM standard solutions of
each dye were prepared individually in different solꢀ
vents (DMSO, DMF, ACN, acetone, chloroform,
octane). According to the polarity index, DMSO is the
most polar, while octane is the least polar [22]. Figure 4
displays the effect of polarity of different solvents in
the emission spectra of D1 and D2 included in this
study. As shown in Fig. 4a, minimal to no shift can be
noted in the D1 emission spectra with an increase in
the solvent polarity. It is interesting, in contrast, to
note that a more pronounced red shift with an increase
in the solvent polarity was observed in D2 emission
spectra than that of D1 (Fig. 4b). Shifts in emission
bands caused by a change in solvent polarity are called
solvatochromic shifts and are experimental evidence
of changes in solvation energy. In fact, the higher is the
polarity of the solvent, the lower is the energy of the
relaxed state and the larger is the redꢀshift of the emisꢀ
sion spectrum. The observed red (bathochromic) shift
with increasing solvent polarity relates to a positive
420 440 460 480 500 520 540 560 580 600 620
Wavelength, nm
Fig. 2. (a) Normalized fluorescence emission spectra
before photobleaching and (b) Fluorescence emission
spectra before and after photobleaching of 10
D2 in ACN, excited at 360 nm.
µ
M
D1 and
solvatochromism and indicates that
a relaxed
D1
D2
intramolecular charge transfer state in D2 is reached.
The above results suggested that D2 is more sensitive
than D1 to the polarity of the microenvironment proꢀ
vided by these solvents
0
200 400 600 800 1000 1200 1400 1600 1800
Time, s
EXPERIMENTAL
Fig. 3. Timeꢀbased fluorescence steadyꢀstate measureꢀ
ments of 10 D1 and D2 in ACN, excited at 360 nm and
monitored at 505 nm with excitation and emission bandꢀ
Chemicals and Reagents
µ
M
Aminophenazone, salicylaldehyde and 2ꢀhydroxyꢀ
1ꢀnaphthaldehyde were obtained from Acros organic
and used without further purification. All solvents
including, dimethyl sulfoxide (DMSO), dimethylforꢀ
mamide (DMF), acetonitrile (ACN), acetone, chloꢀ
roform and octane, used were of high purity and of
analytical reagent grade.
pass set at 15 and 5 nm, respectively.
4ꢀ[(2ꢀHydroxyꢀbenzylidene)ꢀamino] 1,5ꢀdimethylꢀ
2ꢀphenylꢀ1,2ꢀdihydroꢀpyrazolꢀ3ꢀone (D1). A mixture
of 4ꢀaminophenazone, (0.5 g, 2.6 mmol), salicylaldeꢀ
hyde (2.6 mmol) and few drops of piperidine was disꢀ
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536
MARWANI et al.
(а)
D1 Octane
D1 Chloroform
D1 Acetone
D1 ACN
D1 DMF
D1 DMSO
420 440 460 480 500 520 540 560 580 600 620
Wavelength, nm
(b)
D1 Octane
D1 Chloroform
D1 Acetone
D1 ACN
D1 DMF
D1 DMSO
420 440 460 480 500 520 540 560 580 600 620
Wavelength, nm
Fig. 4. Normalized fluorescence emission spectra of 10
chloroform, octane), excited at 360 nm.
µ
M (a) D1 and (b) D2 in different solvents (DMSO, DMF, ACN, acetone,
solved in DMF (3 mL) using a flask. Reaction mixture (C–N); Anal. calcd. for C18H17N3O2: C, 70.34, H,
5.58, N, 13.67, Found: C, 70.28, H, 5.54, N, 13.62.
was irradiated in MW oven for 2 min. After completion
of reaction (by TLC), the mixture was poured into iceꢀ
cold water. The separated solid was filtered, washed
with excess of cold water and dried at room temperaꢀ
4ꢀ[(2ꢀHydroxyꢀnaphthalenꢀ1ꢀylmethylene)ꢀamino]ꢀ
1,5ꢀdimethylꢀ2ꢀphenylꢀ1,2ꢀdihydroꢀpyrazolꢀ3ꢀone (D2)
A mixture of 4ꢀaminophenazone, (0.5 g, 2.6 mmol),
2ꢀhydroxyꢀlꢀnaphthaldehyde (2.6 mmol) and one
drop of piperidine was dissolved in DMF (3 mL) using
a round bottom flask. Reaction mixture was irradiated
in MW oven for 2 min. After completion of reaction
(by TLC), the mixture was poured into iceꢀcold water.
The separated solid was filtered, washed with excess of
cold water and dried at room temperature, a good yield
.
ture, a good yield (85%) of Dye
1 (D1) was obtained
and recrystallized from chloroform and ethanol (8 : 2),
resulting in light yellow crystals.
1
Yield: 85%; Mp 205°C; H NMR (600 MHz
CDCl3)
6.00 (dd,
= 7.8 Hz), 3.24 (s, N–CH3), 2.42 (s, C–CH3); 13
NMR (125 MHz, CDCl3) : 160.62, 149.90, 134.0,
δ: 9.84 (s, 1 H, CHolefinic), 6.96 (d,
J = 8.4 Hz),
J
= 8.4 Hz), 7.38 (dd, = 7.8 Hz), 7.51 (d,
J
J
C
(89%) of Dye
2 (D2) was obtained and recrystallized
δ
from chloroform and ethanol (9 : 1), giving orange yellow
1
132.02, 131.98, 129.31, 127.33, 124.63, 120.20,
crystals. Yield: 89%; Mp 215
°
C; H NMR (600 MHz,
119.10, 35.64, 10.30. IR (KBr) νmax cm–1: 2935 (C–
CDCl3) : 15.26 (s, OH), 10.85 (s, 1H, CHolefinic),
δ
H), 1648 (C=O), 1590 (C=C), 1448 (C=N), 1136 8.26–7.60 (m, 11 Haromatic), 3.20 (s, N–CH3), 2.46 (s,
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GREENꢀSYNTHESIS, CHARACTERIZATION, PHOTOSTABILITY AND POLARITY STUDIES
537
C–CH3)
.
13C NMR (125 MHz, CDCl3): 162.12
,
absorbent and fluorescent. Results of the photostabilꢀ
160.50, 156.80, 149.80, 149.06, 134.25, 133.70, ity study displayed that these Schiff base dyes have a
133.59, 132.17, 13.35, 120.62, 120.53, 119.46, 119.26, high photostability against photobleaching. Fluoresꢀ
116.36, 110.65, 35.31, 10.37. IR (KBr) νmax cm–1: 2956 cence polarity study data of the dyes displayed that D2
(C–H), 1636 (C=O), 1588 (C=C), 1479 (C=N), 1144 is more sensitive than D1 to the polarity of the
(C–N); Anal. calcd. for C22H19N3O2: C, 73.93, H, microenvironment provided by different solvents.
5.36, N, 11.76, Found: C, 73.86, H, 5.31, N, 11.71.
Moreover, solvatochromic shifts were observed in D2
emission spectra upon the change in solvent polarities,
indicating that D2 can be used as solvatochromic
probe. Finally, the preparation and spectroscopic evalꢀ
Sample Preparation
Stock solutions of each dye were individually preꢀ uation of these Schiff base dyes may show considerꢀ
pared in different solvents (DMSO, DMF, ACN, aceꢀ able promise in a range of different applications,
tone, chloroform, octane) and stored in the dark at including analytical, biological and environmental.
4°
C
. For both UVꢀVis spectroscopic and fluorescence Schiff base dyes can exhibit a broad range of biological
measurements, standard solutions of 10 dye were activities, including antifungal, antibacterial, antimaꢀ
also separately prepared in different solvents by adding larial, antiproliferative, antiꢀinflammatory, antiviral,
μM
appropriate amounts of the dye stock solutions.
and antipyretic properties. The azomethane group
present in such compounds has been shown to be critꢀ
ical to their biological activities. In addition, interest
in luminescent dyes has mainly focused on analytical
applications in biological sciences.
Instrumental Methods
Melting points were recorded on a Thomas Hoover
capillary melting apparatus without correction. FTIR
measurements were performed on KBr disks on a
Nicolet Magna 520 FTIR spectrometer. 1H NMR and
13C NMR spectroscopic experiments were recorded in
CDCl3 on a Brucker DPX 600 and 125 MHz specꢀ
trometers, respectively, using tetramethyl silane
(TMS) as an internal standard. Microanalyses were
carried out using a PerkinꢀElmer 240B analyzer. The
UVꢀVis absorption measurements were acquired by
use of a PerkinꢀElmer UVꢀVis scanning spectrophotomꢀ
eter. Absorption spectra were collected using a 10 mm
quartz cuvet. Fluorescence measurements were perꢀ
formed using a PerkinꢀElmer luminescence spectroꢀ
ACKNOWLEDGMENTS
Authors are thankful to the Center of Excellence
for Advanced Materials Research and Chemistry
Department at King Abdulaziz University for providꢀ
ing the research facilities.
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