ISSN 10681620, Russian Journal of Bioorganic Chemistry, 2012, Vol. 38, No. 5, pp. 533–538. © Pleiades Publishing, Ltd., 2012.
GreenSynthesis, Characterization, Photostability and Polarity Studies of Novel Schiff Base Dyes Using Spectroscopic Methods1 Hadi M. Marwania, b, Abdullah M. Asiria, b, and Salman A. Khana, 2 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 salicylalde hyde/2hydroxylnaphthaldehyde with aminophenazone under microwave irradiation. The spectroscopic (FTIR, 1H NMR, 13C NMR, Mass) studies and elemental analyses were in good agreement with chemical structure of synthesized compounds. In addition, UVVis 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 4[(2hydroxybenzylidene)amino]1,5dimemyl2phe nyl1,2dihydropyrazol3one (D1) (6.14%) and 4[(2hydroxynaphthalenlylmethylene)amino]1,5 dimethyl2phenyl1,2dihydropyrazol3one (D2) (2.95%) was observed with an increase in the exposure time using timebased fluorescence steadystate 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 1 to the polarity of the microenvironment provided by different solvents based on the results of fluo rescence polarity studies. Keywords: Schiff bases, pyrazol3one, florescent, photostability DOI: 10.1134/S1068162012050056 21 INTRODUCTION
The application of donor accepter azomethane (HC=N) dyes in science and technology is well known and welldocumented [1, 2]. Azomethane derivatives are coloring magnets and have excellent thermal and optical properties. In addition, these mol ecules have numerous applications such as the optical data storage [3], photoswitching [4], nonlinear optics [5], photochromic materials [1], dyes [6], and chemi cal analysis [7]. On the other hand, wide spectrum of biological activities are associated with these mole cules, such as antimicrobial [8], antifungal [9], antitu mor [10], herbicide [11], inhibition of DNA, RNA, and protein synthesis, nitrogen fixation, and carcino genesis [12]. Furthermore, in the past decade the highdensity 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 DVDR (Digital Ver satile DiscRecordable) 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 1 The article is published in the original. 2 Corresponding author: fax: +966
[email protected].
2
6952292;
email:
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]. Heterocyclic azomethane compounds are exten sively used as metal complexing ligands in spectropho tometry, chromatography and electrophoresis studies since they can advantageously form highly sensitive metal complexes and are easily synthesized and puri fied [15]. 2Hydroxy 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 enolimine and ketoenamine forms (Scheme). In addition, several 2hydroxy Schiff bases, being rela tively simple in structure and exhibiting intramolecu lar proton transfer, have attracted considerable atten tion from both experimental and theoretical points of view [16–20]. The quantum yield of these 2hydroxy 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 pho tobleaching on the photostability of these Schiff bases was investigated by use of timebased fluorescence steadystate measurements. The sensitivity of new
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1.4 Absorbance
1.2 1.0 0.8 0.6 0.4 0.2 0 250
350 400 Wavelength, nm
300
450
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Fig. 1. UVVis absorption spectra of 10 µM D1 and D2 in ACN.
synthesized Schiff bases toward the polarity of the microenvironment provided by different solvents was also examined by fluorescence polarity studies. OH H2N OH + O
N
N
N
2 min MW
CHO
O
N
N
The synthetic route is outlined in Scheme. The FTIR spectra of Schiff bases of pyrazol3one (D1 and D2) showed absorption bands at 2935 and 2956 cm–1 for aromatic C–H and at 1448 and 1479 cm–1 for azome thine group (–CH=N–). The absence of the absorp tion band at 1700–1750 cm–1 also confirms the con version of –CHO group to –CH=N– group. The 1H NMR spectra of hydrazones, as presented in experi 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 azome thine (–CH=N–) proton. The sharp singlet at δ 3.24 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 carbon. The appearance of multiplets at δ 6.96–8.26 was due to aromatic protons. Moreover, 13C NMR spectra showed the signals in the range of δ 119.10 and 116.20 ppm and at δ 134.0 and 134.25 ppm due to aryl carbon and azomethine carbon, respectively. In the EI mass spectrum, a peak appeared at m/z 309 (M +1, 100%), for Dye 1 (D1) having molecular formula (C18H17N3O2). In the mass spectrum of Dye 2 (D2), a peak was observed at m/z 359 (M +1, 100%), which is in consistency with its molecular formula C22H19N3O2. FTIR, 1H 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 synthe sis procedures of the experimental section.
D1
Spectroscopic Evaluation of Dyes H2N HO
CHO + O OH
N
N
N
2 min MW
O
N
N
D2 Scheme. Synthetic route of dyes (D1 and D2).
RESULTS AND DISCUSSION Chemistry Schiff base derivatives (D1 and D2) were prepared by the reaction of 4aminophenazone with the corre sponding active aldehydes by the microwave irradia tion method described previously in the literature [21].
UVVis absorption study. UVVis absorption mea surements of dyes were performed at the same experi 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 UVVis 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. Steadystate fluorescence spectroscopic study. All dyes synthesized in this study fluoresced in the aceto 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 (Fig. 2). However, it can be noticed that there is a blue shift in the emission spectrum of D2 as compared to that of D1, displayed in Figs. 2a and 2b). In addition, Fig. 2b indicates that D2 is slightly dimmer than D1.
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These results are in good agreement with those obtained from UVVis absorption study. Normalized intensity
D1 D2
420 440 460 480 500 520 540 560 580 600 620 Wavelength, nm (b) Relative intensity, a.u.
Polarity study. Polarity plays a major role in many chemical, physical, biochemical and biological phe nomena. In this study, 10 uM standard solutions of each dye were prepared individually in different sol 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 redshift of the emis sion spectrum. The observed red (bathochromic) shift with increasing solvent polarity relates to a positive solvatochromism and indicates that a relaxed 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 pro vided by these solvents
(а)
D1 before photobleaching D1 after photobleaching D2 before photobleaching D2 after photobleaching
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 µM D1 and D2 in ACN, excited at 360 nm.
Relative intensity, a.u.
Photostability study. The photostability study of all dyes was investigated using timebased 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 con 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
0
EXPERIMENTAL Chemicals and Reagents Aminophenazone, salicylaldehyde and 2hydroxy 1naphthaldehyde were obtained from Acros organic and used without further purification. All solvents including, dimethyl sulfoxide (DMSO), dimethylfor mamide (DMF), acetonitrile (ACN), acetone, chlo roform and octane, used were of high purity and of analytical reagent grade. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY
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Fig. 3. Timebased fluorescence steadystate measure ments of 10 µM D1 and D2 in ACN, excited at 360 nm and monitored at 505 nm with excitation and emission band pass set at 15 and 5 nm, respectively.
4[(2Hydroxybenzylidene)amino] 1,5dimethyl 2phenyl1,2dihydropyrazol3one (D1). A mixture of 4aminophenazone, (0.5 g, 2.6 mmol), salicylalde hyde (2.6 mmol) and few drops of piperidine was dis Vol. 38
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Normalized intensity
D1 Octane D1 Chloroform D1 Acetone D1 ACN D1 DMF D1 DMSO
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Normalized intensity
D1 Octane D1 Chloroform D1 Acetone D1 ACN D1 DMF D1 DMSO
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Fig. 4. Normalized fluorescence emission spectra of 10 µM (a) D1 and (b) D2 in different solvents (DMSO, DMF, ACN, acetone, chloroform, octane), excited at 360 nm.
solved in DMF (3 mL) using a flask. Reaction mixture was irradiated in MW oven for 2 min. After completion of reaction (by TLC), the mixture was poured into ice cold water. The separated solid was filtered, washed with excess of cold water and dried at room tempera ture, a good yield (85%) of Dye 1 (D1) was obtained and recrystallized from chloroform and ethanol (8 : 2), resulting in light yellow crystals. Yield: 85%; Mp 205°C; 1H NMR (600 MHz CDCl3) δ: 9.84 (s, 1 H, CHolefinic), 6.96 (d, J = 8.4 Hz), 6.00 (dd, J = 8.4 Hz), 7.38 (dd, J = 7.8 Hz), 7.51 (d, J = 7.8 Hz), 3.24 (s, N–CH3), 2.42 (s, C–CH3); 13C NMR (125 MHz, CDCl3) δ: 160.62, 149.90, 134.0, 132.02, 131.98, 129.31, 127.33, 124.63, 120.20, 119.10, 35.64, 10.30. IR (KBr) νmax cm–1: 2935 (C– H), 1648 (C=O), 1590 (C=C), 1448 (C=N), 1136
(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. 4[(2Hydroxynaphthalen1ylmethylene)amino] 1,5dimethyl2phenyl1,2dihydropyrazol3one (D2). A mixture of 4aminophenazone, (0.5 g, 2.6 mmol), 2hydroxylnaphthaldehyde (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 icecold water. The separated solid was filtered, washed with excess of cold water and dried at room temperature, a good yield (89%) of Dye 2 (D2) was obtained and recrystallized from chloroform and ethanol (9 : 1), giving orange yellow crystals. Yield: 89%; Mp 215°C; 1H NMR (600 MHz, CDCl3) δ: 15.26 (s, OH), 10.85 (s, 1H, CHolefinic), 8.26–7.60 (m, 11 Haromatic), 3.20 (s, N–CH3), 2.46 (s,
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C–CH3). 13C NMR (125 MHz, CDCl3): 162.12, 160.50, 156.80, 149.80, 149.06, 134.25, 133.70, 133.59, 132.17, 13.35, 120.62, 120.53, 119.46, 119.26, 116.36, 110.65, 35.31, 10.37. IR (KBr) νmax cm–1: 2956 (C–H), 1636 (C=O), 1588 (C=C), 1479 (C=N), 1144 (C–N); Anal. calcd. for C22H19N3O2: C, 73.93, H, 5.36, N, 11.76, Found: C, 73.86, H, 5.31, N, 11.71. Sample Preparation Stock solutions of each dye were individually pre pared in different solvents (DMSO, DMF, ACN, ace tone, chloroform, octane) and stored in the dark at 4°C. For both UVVis spectroscopic and fluorescence measurements, standard solutions of 10 μM dye were also separately prepared in different solvents by adding appropriate amounts of the dye stock solutions. 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 spec trometers, respectively, using tetramethyl silane (TMS) as an internal standard. Microanalyses were carried out using a PerkinElmer 240B analyzer. The UVVis absorption measurements were acquired by use of a PerkinElmer UVVis scanning spectrophotom eter. Absorption spectra were collected using a 10 mm quartz cuvet. Fluorescence measurements were per formed using a PerkinElmer luminescence spectro fluorometer equipped with a 20KW for 8 μs duration xenon lamp and gated photomultiplier tube (PMT) and redsensitive R928 PMT detectors. All fluores cence measurements were collected at room tempera ture. The emission spectra of dyes were recorded in a 10 mm quartz fluorescence cuvette and excited at 360 nm excitation wavelength with slit widths set for entrance and exit bandwidths of 2 and 4 nm on both excitation and emission monochromators, respectively. All fluo rescence spectra were blank subtracted before pro ceeding in data analyses. For the photostability study of dyes, timebased fluorescence steadystate mea surements were acquired with excitation and emission bandpass set at 15 and 5 nm, respectively, in order to induce the photobleaching. The excitation and emis sion wavelengths were set at 360 and 505 nm for all dyes included in this study, respectively. The fluence level of the excitation source was open for a period of 30 min. CONCLUSIONS In this study, novel Schiff base dyes were synthe sized via a straightforward route and found to be good RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY
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absorbent and fluorescent. Results of the photostabil ity study displayed that these Schiff base dyes have a high photostability against photobleaching. Fluores cence polarity study data of the dyes displayed that D2 is more sensitive than D1 to the polarity of the microenvironment provided by different solvents. 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 eval uation of these Schiff base dyes may show consider able promise in a range of different applications, including analytical, biological and environmental. Schiff base dyes can exhibit a broad range of biological activities, including antifungal, antibacterial, antima larial, antiproliferative, antiinflammatory, antiviral, and antipyretic properties. The azomethane group present in such compounds has been shown to be crit ical to their biological activities. In addition, interest in luminescent dyes has mainly focused on analytical applications in biological sciences. ACKNOWLEDGMENTS Authors are thankful to the Center of Excellence for Advanced Materials Research and Chemistry Department at King Abdulaziz University for provid ing the research facilities. REFERENCES 1. Ito, Y., Amimoto, K., and Kawato, T., Dyes Pigments, 2011, vol. 89, pp. 319–323. 2. Subik, P., Bialonska, A., and Wolowiec, S., Polyhedron, 2011, vol. 30, pp. 873–879. 3. Liu, C.G., Qiu, Y.Q., Sun, S.L., Chen, H.L.N., and Su, Z.M., Chem. Phys. Lett., 2006, vol. 9, pp. 570–574. 4. Peng, B.H., Liu, L., Liu, D.Z., Jia, K.B., and Yu, J., Photochem. Photobiol. A Chem., 2005, vol. 171, pp. 243–249. 5. Bhat, K., Chang, K.J., Aggarwal, M.D., Wang, W.S., Penn, B.G., and Frazier, D.O., Mater. Chem. Phys., 1996, vol. 44, pp. 261–266. 6. Nejati, K., Rezvani, Z., and Massoumi, B., Dyes Pig ments, 2007, vol. 75, pp. 653–657. 7. Fernandez, G.J.M., Portilla, F.D.R., Garcia, B.Q., Toscano, R.A., and Salcedo, R.J., Mol. Struct., 2001, vol. 561, pp. 197–207. 8. Asiri, A.M. and Khan, S.A., Molecules, 2010, vol. 15, pp. 6850–6858. 9. Chohan, Z.H., Sumrra, S.H., Youssoufi, M.H., and Hadda, T.B., Eur. J. Med. Chem., 2010, vol. 45, pp. 2739–2747. 10. Sun, T., Zhu, Y., Xie, J., and Yin, X., Bioorg. Med. Chem. Lett., 2011, vol. 21, pp. 798–800. 11. Akelah, A., Kenawy, E.R., and Sherringto, D.C., Eur., Polym. J., 1993, vol. 29, pp. 1041–1045. Vol. 38
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18. Popovic, Z., Roje, V., Pavlovic, G., MatkovicCal ogovic, D., and Giester, G., J. Mol. Struct., 2001, vol. 597, pp. 39–47. 19. Joshi, H., Kamounah, F.S., Gooijer, C., Vander, Z.G., and Antonov, L.J., Photochem. Photobiol. A Chem., 2002, vol. 152, pp. 183–191. 20. Herzfeld, R. and Nagy, P., Curr. Org. Chem., 2001, vol. 5, pp. 373–394. 21. Naqvi, A., Shahnawaaz, M., Rao, A.V., Seth, D.S., and Sharma, N.K., El. J. Chem., 2009, vol. S6, pp. 75–S78. 22. Snyder, L.R., J. Chromatogr. Sci., 1978, vol. 16, pp. 223–234.
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