ОПТИКА И СПЕКТРОСКОПИЯ, 2015, том 118, № 1, с. 70-75
СПЕКТРОСКОПИЯ КОНДЕНСИРОВАННОГО СОСТОЯНИЯ
y%K 543.42
FLUORESCENCE PROPERTIES OF DIENONE DERIVATIVES AND SOLVENT EFFECTS ON THEIR FLUORESCENCE ABSORPTION AND EMISSION
© 2015 r. P. Ruanwas*, S. Chantrapromma*, C. Karalai*, C. S. Chidan Kumar**
* Department of Chemistry and Center of Excellence for Innovation in Chemistry, Faculty of Science, Prince of Songkla University, Hat-Yai, Songkhla 90112, Thailand ** Department of Engineering Chemistry, Alva's Institute of Engineering and Technology, Mijar,
Moodbidri 574225, Karnataka, India E-mail: suchada.c@psu.ac.th Received May 20, 2014
Five dienone derivatives, (1E,4E)-1,5-bis(4-R-phenyl)penta-1,4-dien-3-one (1-5), R = OH (1), OCH3 (2), OCH2CH3 (3), N(CH3)2 (4) and N(CH2CH3)2 (5) have been synthesized and characterized by 1H- and 13C-NMR, UV-Vis and FT-IR spectroscopy and investigated for their fluorescence properties. The compounds under test possess fluorescence properties. The fluorescence absorption and emission maxima of 1-5 were found in the range 421-431 nm and 514-555 nm, respectively, leading to Stokes shifts ranging from 4099 to 5735 cm-1. Further, the effects of solvents on labs (absorption) and lem (emission) of 4 and 5 were determined and noticed that the absorption spectra of these compounds were not significantly altered. While, the emission peak of 4 was shifted in CHCl3 (red shift) and 5 was shifted in EtOH (red shift) and hexane (blue shift). Analysis revealed that the compounds 4 and 5 are promising fluorescent probes with good fluorescence properties.
DOI: 10.7868/S0030403415010213
INTRODUCTION
Curcumin (1,7-bis(4-hydroxy-3-methoxyphenyl)-1,6-heptadiene-3,5-dione) (Fig. 1a) is a yellow-orange pigment isolated from Curcuma longa, popularly known as turmeric. It is used as a dietary pigment, spice, and traditional medicine in India and China from decades. Curcumin and its derivatives are proven as fluorescent probes, with their emission properties highly dependent on the polarity of its environment [1]. It has wide applications in the field of pharmaceuticals as preventer of skin from sun burns and any ailments like leucoderma etc. [2, 3]. In addition, it is also well known as a potent antioxidant [4-6], antibacterial [6, 7] and anticancer [8, 9] material, including pho-tobiological and photosensitizing activities [10, 11]. Though curcumin is a fascinating molecule which exhibits wide applications, it lacks for bioavailability and instability at neutral to basic conditions. To overcome the lack of bioavailability, many a, p-unsaturated ke-tone were modified and investigated their biological [12, 13] and photo-physical properties [14, 15]. Many researchers studied and reported some closely related dienone derivatives (Fig. 1b) investigating their potency towards biological activities [16-19] and fluorescence properties [20]. Some dienone derivatives in this work were reported on utilizing as probes for p-amy-loid plaques [21], fluoroionophores for various cations [22] and two photon absorbers for polymer initiators
[23]. However, there are only few reports explaining their ability to fluorescence.
The above findings led us to synthesize a series of mono-carbonyl analogues of curcumin by removing the p-diketone moiety. The synthesized compounds are examined for their ability for fluorescence properties and to study the solvent effects on the fluorescence. In the present study, five dienone derivatives (Fig. 2) namely (1E,4E)-1,5-bis(4-hydroxyphe-nyl)penta-1,4-dien-3-one (1), (1E,4E)-1,5-bis(4-methoxyphenyl-penta-1,4-dien-3-one (2), (1E,4E)-1, 5 -bis(4 - ethoxyphenyl) -penta-1,4- dien- 3 - one (3),
(a)
H3CO
HO
OCH3 OH
(b) O
R
R
Fig. 1. Molecular structures of (a) curcumin and (b) dienone derivatives.
FLUORESCENCE PROPERTIES OF DIENONE DERIVATIVES CHO O
NaOH (aq) p^^2331^ pp-----------------—^s^551^ jj"—
O
+ 2
stirred at RT
R
R
Fig. 2. Synthesis of (1E,4E)-1,5-bis(4-R-phenyl)penta-1,4-dien-3-one (1-5): (1) R=OH, (2) R=OCH3, (3) R=OCH2CH3, (4) R=N(CH3)2, (5) R=N(CH2CH3)2.
(1E,4E)-1,5-bis(4-dimethylaminophenyl)penta-1,4-dien-3-one (4), (1E,4E)-1,5-bis(4-diethylaminophe-nyl)-penta-1,4-dien-3-one (5) have been synthesized and investigated for their fluorescence. In addition, the effects of solvents on the fluorescence properties were also carried out.
RESULTS AND DISCUSSION
Absorption and Emission Spectra
The absorption and emission spectra of compounds (1-5) with the concentration 10-5 M, were measured in DMSO at room temperature (RT). Spectroscopic data such as absorption emission maxima, fluorescence quantum yields, Stokes shifts are listed in Table 1. The absorption and fluorescence emission occurs in the region of 324-458 and 443-568 nm, respectively, which are depicted in Fig. 3. The UV-Vis absorption spectra indicated that the compounds (1-5) under test exhibit absorption bands at 353, 324, 324, 383 and 458 nm, which were assigned to n-n* electronic transition. Among the tested compounds (1-5), the absorption band of compound 5 showed red shift, at a longer wavelength. This is attributed due to the presence of electron donating diethylamino substituent, N(CH2CH3)2, leading to the electron delocaliza-tion within the molecule. The fluorescence emission studies (Table 1 and Fig. 3), showed emission bands in the range of 443-568 nm. Interestingly, the fluorescence emission maxima of the compounds 4 and 5 upon excitation at 390 nm were noticed at 483 (O^ = 0.18) and 568 (O^ = 0.16) nm, respectively. This interesting
Table 1. UV-Vis absorption (labs) and emission (lem) maxima of the compounds (1-5) in DMSO
Compounds R ^abs> nm ^em, nma Stokes shift of
1 OH 353 443 90 0.0015
2 OCH3 324 452 128 0.0004
3 OCH2CH3 324 447 123 0.0007
4 N(CH3)2 383 483 100 0.1825
5 N(CH2CH3)2 458 568 110 0.1602
a Excited at 390 nm. b
Fluorescence quantum yield which use coumarin-7 as standard.
phenomenon is mainly due to strong electron donating substituent N(CH3)2 and N(CH2CH3)2 in compounds 4 and 5, respectively, that has influenced on the red shift with higher intensity in the emission peak. Comparatively, the weaker emission intensities were observed for the compounds (1—3) bearing OH in 1, OCH3 in 2 and OCH2CH3 in 3 which are considered as weaker electron donating groups than the N(CH3)2 in 4 and N(CH2CH3)2 in 5 substituent. Hence, the compounds 4 and 5 were chosen and subjected for further studies to explore the effect of solvents (DMSO, acetone, EtOH and hexane) on their fluorescence properties.
Solvent Effects on the Absorption and Emission Fluorescence Spectra of 4 and 5
Compounds 4 and 5 were further studied for the solvent effects due to their highest quantum yield (Fig. 3 and Table 1). The general properties of the solvents used for the study were given in Table 2. The observed absorption (^abs) and emission (^em) spectra of the compounds 4 and 5 in different solvents are depicted in Fig. 4 and the normalized absorption and emission intensities of compounds 4 and 5 in various solvents were given in Table 3. The absorption spectra of 4 and 5 in various solvents (DMSO, acetone, EtOH and hexane) were not altered and appeared in the same range of 356—383 nm for 4 (Fig. 4a), and 410—468 nm for 5 (Fig. 4b), indicating that there is no significant change in the transition state. The emission results revealed that, the emission peak of compound 4 (Fig. 4c) in hexane (430 nm) was slightly shifted to the shorter wavelength compared to DMSO, acetone, and EtOH (461—486 nm). A similar observation was found for the compound 5 (Fig. 4d) in hexane, DMSO and acetone (Table 3). Whereas the emission peak in EtOH was shifted to the longer wavelength (610 nm) (Fig. 4d). Notably, the emission peaks were observed at different wavelengths. In general, the increment of solvent polarity contributes the molecule to reduce the energy level of the excited state, while the decrease in solvent polarity reduces the solvent effect on the excited state energy level [24]. Furthermore, in case of compound 5, the shift in emission wavelengths subjecting to various solvents may also occurred due to hydrogen bonding interactions between fluorophore and the solvent. From Fig. 5, it is clearly seen that compound 5 exhibits
three different fluorescence colors in nine different solvents under UV light, producing the red fluorescence in polar protic solvents (MeOH and EtOH), and yellow fluorescence in polar aprotic solvents (DMSO, acetronitrile, CHCl3, acetone and EtOAc), and green fluorescence in non-polar solvents (toluene and hexane).
EXPERIMENTAL
Instrumentation
All the chemical reagents and solvents were of analytical grade, purchased commercially, and used without further purification. Melting point (mp) was recorded using an Electrothermal melting point apparatus. Infrared spectra were recorded by using FTS 165 FT-IR spectrophotometer. Ultraviolet-Visible (UV-Vis) absorption spectra were recorded using a Shimad-zu UV-2450 UV-Visible spectrophotometer. The 1H-and 13C—NMR spectra were recorded from 300 MHz Bruker FTNMR Ultra Shield™ spectrometer in CDCl3 with TMS as internal standard. Chemical shifts reported in ppm and are expressed in Hertz. Fluorescence excitation and emission spectra were recorded on a Perkin-Elmer LS 55 luminescence spectrometer in different solvents at the ambient temperature.
2.0 1.6 1.2
a
-S3
S0.4 -q
(a)
/ k / /
I--/X'' \ f \y V \ JJl
/ 7 V-\
5
ö s
43
a
230
40
30
20
o
E
10
0 400
280
i v
330
380
430
480 530 Wavelength, nm
(b)
v !
v h I \
500 600 700 800 Wavelength, nm
Fig. 3. Absorption (a) and emission (b) spectra of the compounds (1—5).
2
3
5
Synthesis
Compounds 1—5 were synthesized by reacting the corresponding benzaldehyde [4-hydroxybenzalde-hyde for (1), 4-methoxybenzaldehyde for (2), 4-ethoxybenzaldehyde for (3), 4-dimethylaminobenzal-dehyde for (4) and 4-diethylaminobenzaldehyde for (5)] (6 mmol) and acetone (3 mmol) in ethanol (30 mL)
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