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Synthesis, characterization and fluorescence studies of novel bi-phenyl based acrylate and methacrylate
Spectrochimica Acta Part A 79 (2011) 1992–1997
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy journal homepage: www.elsevier.com/locate/saa
Synthesis, characterization and fluorescence studies of novel bi-phenyl based acrylate and methacrylate R. Baskar, K. Subramanian ∗ Department of Chemistry, Anna University, Chennai, India
a r t i c l e
i n f o
Article history: Received 28 March 2011 Received in revised form 26 May 2011 Accepted 30 May 2011 Keywords: Chalcone 2D NMR Fluorescence
a b s t r a c t 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenyl prop-2-enoate (ACH) and 4-[(1E)-3-(biphenyl-4yl)buta-1,3-dien-1-yl]phenyl 2-methylprop-2-enoate (MCH) was synthesized from biphenyl in three steps and their structures were confirmed by elemental analysis, IR, NMR (1 H, 13 C, DEPT135, 1 H–1 H COSY, 1 H–13 C HSQC and 1 H–13 C HMBC) spectroscopic techniques. In this present study, various physicochemical characteristics we demonstrate solubility, color, absorbance and fluorescence property of novel biphenyl based acrylate and methacrylate measured in different solvents like benzene, dichloromethane, tetrahydrofuran, acetonitrile, dimethylsulfoxide and ethanol. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Fluorescent compounds are widely useful in chemical sensors, fluorescent labelling, dyes and biological detectors. Biphenyl is an excellent chromosphore and its metal complexes show strong light emitting properties and long fluorescence life times. Further biphenyl based compounds are useful for redox and fluorescent sensors [1–3]. Most of the chalcones and their derivatives find useful in medical therapy, optical materials and polymeric UVabsorption filters [4]. These are precursors of various naturally occurring pigments [5]. Chalcones separated by bichromophoric moieties such as vinyl chains and carbonyl group were found to be effective photosensitive materials [6,7]. Several synthetic chalcones were reported as antineoplastic agents [8–10] as well as active against malaria, cardiovascular diseases and tuberculosis [11–14]. In this present study, we report the synthesis of novel
biphenyl based acrylate and methacrylate, which has excellent fluorescent property. Their structures were characterized using modern NMR spectroscopy 2D techniques like 1 H–1 H COSY, 1 H–13 C HSQC and 1 H–13 C HMBC. 2. Experimental 2.1. Materials and methods Bi-phenyl, 4-hydroxy benzaldehyde, acetyl chloride, aluminium trichloride, nitrobenzene, potassium hydroxide, triethylamine, ethylmethylketone, acryloyl chloride and methacryloyl chloride were purchased from Merck, and used without further purification. Solvents were purified and dried in accordance with the standard procedure [15]. 2.2. Physical measurements
General structure of compounds ACH (R = H) and MCH (R = CH3) (Numbering is given for better understanding in discussions)
∗ Corresponding author. Tel.: +91 44 22358660. E-mail address: [email protected] (K. Subramanian). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.05.105
The infrared spectra were recorded using Perkin Elmer spectrum one instrument in the frequency range 4000–450 cm−1 , using KBr pellet method. NMR spectra were recorded using BRUKER 500 MHz AVANCE III instrument using CDCl3 as solvent, with TMS as an internal standard. The DEPT135 spectrum was recorded in standard manner = 135 pulse program, 2D techniques 1 H–1 H COSY, geHSQC and ge-HMBC spectra were recorded by using the standard Bruker pulse programs. The electronic spectra was recorded by UV1601 Shimadzu UV-Visible spectrophotometer in different solvents in the range of electronic absorbance between 200 and 800 nm. The fluorescence emission spectra were recorded using Perkin Elmer LS55 fluorescence spectrophotometer, using the excitation wavelength of the respective absorption maxima for different solvents.
R. Baskar, K. Subramanian / Spectrochimica Acta Part A 79 (2011) 1992–1997
2.3. Synthesis 2.3.1. 4-Acetyl biphenyl (AB) Acetyl biphenyl was prepared as described in the literature [16]. Anhydrous aluminium trichloride (3.24 mmol) is added with 60 ml of nitrobenzene at ambient temperature under nitrogen atmosphere. To the above mixture, biphenyl (3.24 mmol) was added slowly with constant stirring followed by drop wise addition of acetyl chloride (3.24 mmol) at 0 ◦ C and the stirring was continued for 4 h. The reaction mixture was neutralized with sodium bicarbonate solution and extracted with ethyl acetate. The organic phase was washed with brine solution, and dried over anhydrous sodium sulphate. Volatiles were removed through vaccum and nitro benzene was removed by vaccum distillation. The residue was recrystalised using ethanol. Compound obtained as gray color solid Yield: 70%. m.p.: 118 ◦ C. 1 H NMR (500 MHz, CDCl3 ) ı ppm 2.66 (s, 3H), 7.43 (t, J = 7.55 Hz, 1H), 7.50 (t, J = 7.33 Hz, 2H), 7.66 (d, J = 8.20 Hz, 2H), 7.71 (d, J = 8.37 Hz, 2H), 8.06 (d, J = 8.50 Hz, 2H). 13 C NMR (126 MHz, CDCl3 ) ı ppm 26.65, 127.23, 128.23, 128.96, 135.89, 139.90, 145.84, 197.76. IR (KBr, cm−1 ) 1670, 2915, 2999.
2.3.2. 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenol (HCH) 4-Acetyl biphenyl (10.2 mmol) in methanol (30 ml) with potassium hydroxide (0.0408 mol). To the above reaction mixture, 4-hydroxy benzaldehyde (10.2 mmol) in 10 ml of methanol was added drop wise with constant stirring at 60 ◦ C. The reaction mixture was refluxed for 24 h; it was neutralized with dilute hydrochloric acid and extracted using ethyl acetate. The organic layer was washed with brine solution, dried over anhydrous sodium sulphate. Volatiles were removed through vaccum and purified by column chromatography. Compound obtained as yellow solid Yield: 72%. m.p.: 203 ◦ C. 1 H NMR (500 MHz, CDCl3 ) ı ppm 6.92 (d, J = 8.50 Hz, 2H), 7.41 (t, J = 7.25 Hz, 1H), 7.48 (t, J = 7.57 Hz, 2H), 7.54 (d, J = 15.76 Hz, 1H) 7.64 (d, J = 7.26 Hz, 2H), 7.67–7.71 (d, J = 8.51 Hz, 2H), 7.73 (d, J = 8.51 Hz, 2H), 7.79–7.87 (d, J = 15.45 Hz, 1H), 8.10 (d, J = 8.51 Hz, 2H). 13 C NMR (126 MHz, CDCl3 ) ı ppm 116.33, 119.04, 127.38, 127.47, 128.79, 129.56, 131.30, 131.50, 137.30, 139.49, 144.69, 144.93, 160.65, 188.93. IR (KBr, cm−1 ) 1639, 1511, 2986, 3312.
2.3.3. 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenyl prop-2-enoate (ACH) 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenol (3.3 mmol) in 20 ml of ethyl methyl ketone with triethylamine (3.6 mmol). To the above mixture, acryloylchloride (3.3 mmol) was added drop wise at 0 ◦ C. The mixture was stirred for 24 h at room temperature and is washed with excess of water and extracted with dichloromethane. The organic layer was washed with brine solution and dried over anhydrous sodium sulphate. Volatiles were removed through vaccum and purified by column chromatography. Compound obtained as pale yellow solid Yield: 79%. m.p.: 124 ◦ C. 1 H NMR (500 MHz, CDCl3 ) ı ppm 6.06 (t, J = 10.5 Hz, 1H unsaturated proton), 6.36 (dd, J = 17.5 Hz, 10.5 Hz, 1H unsaturated proton), 6.66 (dd, J = 17.5 Hz, 5 Hz, 1H unsaturated proton), 7.24 (d, J = 8.74 Hz, 2H), 7.43 (t, J = 7.43 Hz, 1H), 7.50 (t, J = 7.21 Hz, 2H), 7.58 (d, J = 15.73 Hz,1H), 7.67 (d, J = 7.43 Hz, 2H), 7.68 (d, J = 8.56 Hz, 2H), 7.75 (d, J = 8.03 Hz, 2H), 7.84 (d, J = 15.69 Hz, 1H), 8.12 (d, J = 8.38 Hz, 2H). 13 C NMR (126 MHz, CDCl3 ) ı ppm 122.18, 122.33, 127.32, 127.36, 127.44, 128.24, 128.97, 129.14, 129.62, 131.23, 132.72, 136.84, 139.93, 143.65, 145.65, 152.25, 164.21, 189.86. IR (KBr, cm−1 ) 1504, 1284, 1700, 1754, 2926, 3045, 3060. Anal. Calcd for C24 H18 O3 (MW 354.13): C, 81.34; H, 5.12; O, 13.54. Found: C, 81.26; H, 5.17; O, 13.72.
1993
Table 1 Infrared spectral data (cm−1 ) for ACH and MCH. Vibrations
ACH
MCH
C O (˛-ˇ-unsaturated) C O (aromatic ester) C–O (stretching) C C (˛-ˇ-unsaturated) C C (stretching) C–H (aliphatic methyl) stretching C–H (aromatic) C C (bending vibration) C–H (aliphatic methyl) bending
1700(s) 1754(s) 1284(s) 3045(w) 3060(w)
1659(s) 1726(s) 1318(s) 3042(s) 3058(w) 2853(w) 2926(w) 1504(w) 1416(w)
2926(w) 1504(w)
(s) – Strong; (w) – weak.
2.3.4. 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenyl 2-methylprop-2-enoate (MCH) 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenol (3.3 mmol) in 20 ml of ethylmethylketone with triethylamine (3.6 mmol). To the above mixture, methacryloylchloride (3.3 mmol) was added drop wise at 0 ◦ C. The mixture was stirred 24 h at room temperature, washed with excess of water and extracted using dichloromethane. The organic layer was washed with brine solution dried over anhydrous sodium sulphate. Volatiles were removed through vaccum and purified by column chromatography. Compound obtained as pale yellow solid Yield: 78%. m.p.: 124 ◦ C. 1 H NMR (500 MHz, CDCl3 ) ı ppm 2.08 (s, 3H) 5.79 (s, 1H unsaturated proton), 6.37 (s, 1H unsaturated proton), 7.21 (d, J = 8.51 Hz, 2H), 7.41 (t, J = 7.25 Hz, 1H), 7.48 (t, J = 7.57 Hz, 2H), 7.54 (d, J = 15.76 Hz,1H), 7.64 (d, J = 7.26 Hz, 2H), 7.67–7.71 (d, J = 8.51 Hz, 2H), 7.73 (d, J = 8.51 Hz, 2H), 7.79–7.87 (d, J = 15.45 Hz, 1H), 8.10 (d, J = 8.51 Hz, 2H); 13 C NMR 126 MHz, CDCl3 ) ı ppm 13.37, 122.08, 122.29, 127.31, 127.33, 127.75, 128.25, 128.99, 129.16, 129.64, 132.58, 135.66, 136.84, 139.93, 143.49, 145.63, 152.63, 165.56, 189.90. IR (KBr, cm−1 ) 1318, 1416, 1504, 1659, 1726, 2853, 2926, 3042, 3058. Anal. Calcd for C25 H20 O3 (MW 368.14): C, 81.50; H, 5.47; O, 13.03. Found: C, 81.46; H, 5.54; O, 13.17. 3. Results and discussion The compounds of ACH and MCH were pale yellow powder; the analytical data for the complexes were in good agreement with the above molecular formula. The compound HCH having hydroxyl group was confirmed by spectral data. The preparation of compound HCH was achieved by Aldol condensation reaction of compound AB and 4-hydroxy benzaldehyde in the presence of a strong base like KOH as catalyst. Compounds ACH and MCH were synthesized by esterification reaction of compound HCH and corresponding acid chlorides in the presence of triethylamine. 3.1. Solubility Compounds ACH and MCH were found to be soluble in polar aprotic solvents like dimethyl sulfoxide, dimethylformamide, acetonitrile, dichloromethane, tetrahydrofuron, ethyl acetate, acetone and in non-polar solvent like chloroform. But the compounds were sparingly soluble in polar protic solvents like ethanol, methanol and in non-polar solvents like benzene. Compounds were completely insoluble in water. 3.2. IR spectra Generally ˛-ˇ-unsaturated esters show carbonyl stretching frequency at 1659 cm−1 but the compound MCH showed stretching vibration at 1700 cm−1 due to inductive effect of the methyl group. Compounds ACH and MCH showed aromatic stretching at 2926 cm−1 . The aliphatic methyl C–H stretching of compound
1994
R. Baskar, K. Subramanian / Spectrochimica Acta Part A 79 (2011) 1992–1997
Table 2 1 H and 13 C NMR data, 1 H–1 H COSY, 1 H–13 C HSQC and 1 H–13 C HMBC correlations of MCH. Carbon number
C1 C2 C2 C3 C4 C5,C5 C6,C6 C7 C8 C9 C10 C11 C12,12 C13,C13 C14 C15 C16,C16 C17,C17 C18
1
Chemical shift (ppm) ıH
ıC
Ha 5.83 (1H, s) Hb 6.84 (1H, s) – 2.03(3H, s) – – 7.21 (d, J = 8.51 Hz, 2H) 7.67–7.71 (d, J = 8.51 Hz, 2H) – 7.79–7.87 (d, J = 15.45 Hz, 1H) 7.54 (d, J = 15.76 Hz,1H) – – 8.10 (d, J = 8.51 Hz, 2H) 7.73 (d, J = 8.51 Hz, 2H) – – 7.64 (d, J = 7.26 Hz, 2H) 7.49 (2 H, t, J = 7.09 Hz) 7.41 (t, J = 7.25 Hz, 1H)
127.75 135.66 18.37 165.56 152.63 122.29 129.64 132.58 143.49 122.08 189.90 136.84 129.16 127.33 145.63 139.93 127.31 128.99 128.25
H–1 H COSY
H–13 C HSQC
1
1
H–13 C HMBC
( J)
( J)
(3 J)
H2
127.75
135.66(C2)
165.56(C3) 18.37(C2 )
– Ha , Hb
– 18.37 – – 122.29 129.64 – 143.49 122.08 – – 129.16 127.33 – – 127.31 128.99 128.25
135.66(C2)
165.56(C3) 127.75(C1)
152.63(C4) 132.58(C7)
132.58(C7) 152.63(C4) 143.49(C8)
132.58(C7) 122.08(C9) 189.90(C10)
129.64(C6) 189.90(C10) 132.58(C7)
127.33(13) 129.16(C12)
145.63(C14) 189.90(C10) 136.84(C11) 139.93(C15)
128.99(C17) 127.31(C16)128.28(C18) 128.99(C17)
145.63(C14)128.25(C18) 139.93(C15) 127.31(C16)
H6 H5 – H9 H8 – H13 H12
H17 H16
MCH appeared at 2853 cm−1 . The vibrational stretching frequency appeared at 1318 cm−1 was due to the presence of C–O–C linkage. The vinylic carbon shows vibration at 3050 cm−1 in compounds ACH and MCH. The vibration patterns are given in Table 1. The bands observed at region between 1000 and 800 cm−1 were the characteristic bands of C–H out of plane bending or vagging vibration of hydrogen atom attached to unsaturated carbons [20], relatively weaker absorption band at 1504 cm−1 is due to bending modes of ˛-ˇ-unsaturated carbons. Alkyl C–H bending vibration was observed at 1416 cm−1 in compound MCH, where as this vibration was not observed with ACH. 3.3. 1D and 2D NMR spectra In 1 H NMR spectrum of compounds ACH and MCH two doublets were observed at 7.54 (J = 15.76 Hz) and 7.81 (J = 15.45 Hz) which has been assigned to H8 and H9, the J value of these protons confirmed the product as a trans isomer (Figs. 3 and 4). All the compounds were exhibiting two triplets at 7.49 ppm and 7.41 ppm and were assigned to H17 and H18 respectively. The remaining 5
Fig. 1. Fluorescence spectra of ACH.
1
2
doublets were observed at 7.21 ppm, 7.69 ppm, 8.10 ppm, 7.73 ppm, 7.64 ppm, which had been assigned to H5, H6, H12, H13 and H16 respectively. The compound MCH showed one singlet at 2.03 ppm with three protons which corresponds to H2 methyl proton and two singlets were observed at 5.83 ppm and 6.84 ppm that corresponds to Ha and Hb. The singlet Hb is cis to carbonyl group which appeared in the down field region due to the presence of rich electron density around carbonyl oxygen when compared to Ha singlet. In the 13 C NMR spectra of the compound MCH, methyl (C2 ) carbon and olefinic (C1) carbon resonance were observed at 18.37 and 127.75 ppm respectively. 1 H–1 H COSY spectrum (Fig. 5) displayed scalar couplings for adjacent protons like H5 ↔ H6, H8 ↔ H9, H12 ↔ H13 and H16 ↔ H17. Further, the connection between these fourteen protons and its parent carbons namely C5 (122.29), C8 (143.49), C12 (129.16), C16 (127.31), C6 (129.64), C9 (122.08), C13 (127.33) and C17 (128.99), were confirmed by direct couplings in HSQC spectrum (Fig. 6). One triplet observed at ıH = 7.41 ppm is very closer to H17 its 1 H–1 H COSY scalar coupling correlation was very difficult, the 1 H–13 C correlation 1 H–13 C HSQC spectrum gives direct correlation to C18 (128.25). It was interesting to note that the
Fig. 2. Fluorescence spectra of MCH.
R. Baskar, K. Subramanian / Spectrochimica Acta Part A 79 (2011) 1992–1997
Fig. 3.
1
H NMR spectrum of ACH.
13 C NMR resonances for C2, C7 and C11 quaternary carbons were observed at 135.66 ppm, 132.58 ppm and 136.84 ppm respectively were obtained only in 1 H–13 C HMBC spectrum and not obtained in COSY and HSQC. The DEPT135 spectrum showed the disappearance of 13 C resonance at 135.66 ppm, 165.56 ppm, 152.63 ppm, 132.58 ppm, 189.90 ppm, 136.84 ppm, 145.63 ppm, 139.93 ppm, indicating that they were directly attached to proton bearing carbons. The higher chemical shift value observed at 189.90 ppm was due to C10 carbonyl carbon, and the next highest chemical shift was observed at 165.56 ppm was due to C3 carbonyl carbon, remaining were quaternary carbons, which was observed at stack plot of 13 C and DEPT spectrum. The HMBC spectrum was very useful for the assignment of six quaternary carbons. In HMBC correlation spectrum, the two olefinic protons (Ha and Hb ) showed the strong three bond coupling with C2 carbon, the H9 (7.54 ppm) and H13 (7.73) protons showed the three bond coupling with C7 (132.58) and C11 (136.84) respectively. The quaternary carbons C4 (152.63), C14 (145.63) and C15 (139.93) were well understood from HMBC
Fig. 4.
1
1995
correlation spectrum. 1 H, 13 C NMR data, 1 H–1 H COSY, 1 H–13 C HSQC and 1 H–13 C HMBC correlations are given in Table 2 (Fig. 7). 3.4. UV–vis spectra The absorption bands around 270–320 nm is characteristic peaks of chalcone moiety, the absorption maximum and extinction coefficient values are given in Table 3. The effect of solvent polarity is termed as solvatochromism [17]. The absorption maximum values (max ) for both compounds increase with increase in the solvent polarity. The compounds show bathochromic (red) shift at high by polar solvents. As a result, the compounds show → * transition in polar solvents. The compound ACH shows max at 330 nm and 338 nm in the solvents DMSO and ethanol respectively. The compound MCH shows max at 319 nm and 323 nm in DMSO and ethanol respectively. Because, the excited state is more dipolar than the ground state and the electronic transition energy decreases with increase in the polar solvent [18].
H NMR spectrum of MCH.
1996
R. Baskar, K. Subramanian / Spectrochimica Acta Part A 79 (2011) 1992–1997
Table 3 Electronic absorption and emission spectral data (bands) of ACH and MCH. Solvents
ACH
Ethanol DMSO Acetonitrile THF Dichloromethane Benzene
MCH
max (nm)
A
εmax (M−1 cm−1 )
em (nm)
F
max (nm)
A
εmax (M−1 cm−1 )
em (nm)
F
338 330 316 291 271 270
1.98 0.220 1.445 2.027 0.648 0.495
19,800 2,200 14,450 20,270 6,480 4,950
410 403 381 382 374 380
0.124 0.241 0.932 0.299 0.307 0.087
323 319 321 284 281 278
1.608 0.187 2.083 1.175 0.960 0,653
16,050 1,870 20,830 11,750 9,600 6,530
382 384 381 382 380 373
0.797 0.903 0.150 0.549 0.535 0.296
Fig. 5.
1
Fig. 7.
H–1 H COSY NMR spectrum of MCH.
1
H–13 C HMBC NMR spectrum of MCH.
3.5. Fluorescence spectra The emission maxima and its intensity in different solvents for compounds ACH and MCH are given in Table 3. em emission of compound ACH showed in polar solvents DMSO and ethanol were very high (403 nm, 410 nm) when compared to the non-polar solvent benzene(380 nm). The difference between the emission maxima and excitation maxima (Stokes shift) was higher in the polar solvents like DMSO and ethanol where as lesser in benzene Stokes shift [19]. Compound MCH also showed maximum intense emission and emission maxima in solvents DMSO and ethanol. Its emission maxima (em ) were 382 nm and 384 nm respectively. The emission spectra showed gradual red shift when the solvent polarity was changed from lower to higher. This is due to the fact that the excited state of the compounds is more stable than the ground state of high polar solvents when compared to that of the low polar solvents. The fluorescence emission spectra of compounds ACH and MCH are given in Figs. 1 and 2. 4. Conclusion
Fig. 6.
1
H–13 C HSQC NMR spectrum of MCH.
In this present study, we have synthesized a novel biphenyl based fluorescent compound, and their structure has been confirmed by different 1D and 2D NMR techniques. The compound ACH showed the em emission maximum in ethanol and DMSO, and the compound MCH also showed the maximum emission in ethanol and DMSO. The absorbance, emission, color, intensity of
R. Baskar, K. Subramanian / Spectrochimica Acta Part A 79 (2011) 1992–1997
fluorescence and solubility of both the compounds were investigated in different organic solvents.
[9]
Acknowledgements [10]
The authors are grateful to acknowledge SAIF, IIT-Madras for supporting in all the spectroscopic studies. We thank Dr. V. Kesavan, Department of Bio-technology, IIT-Madras for his support in this work.
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Synthesis, characterization and fluorescence studies of novel bi-phenyl based acrylate and methacrylate R. Baskar, K. Subramanian ∗ Department of Chemistry, Anna University, Chennai, India
a r t i c l e
i n f o
Article history: Received 28 March 2011 Received in revised form 26 May 2011 Accepted 30 May 2011 Keywords: Chalcone 2D NMR Fluorescence
a b s t r a c t 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenyl prop-2-enoate (ACH) and 4-[(1E)-3-(biphenyl-4yl)buta-1,3-dien-1-yl]phenyl 2-methylprop-2-enoate (MCH) was synthesized from biphenyl in three steps and their structures were confirmed by elemental analysis, IR, NMR (1 H, 13 C, DEPT135, 1 H–1 H COSY, 1 H–13 C HSQC and 1 H–13 C HMBC) spectroscopic techniques. In this present study, various physicochemical characteristics we demonstrate solubility, color, absorbance and fluorescence property of novel biphenyl based acrylate and methacrylate measured in different solvents like benzene, dichloromethane, tetrahydrofuran, acetonitrile, dimethylsulfoxide and ethanol. © 2011 Elsevier B.V. All rights reserved.
1. Introduction Fluorescent compounds are widely useful in chemical sensors, fluorescent labelling, dyes and biological detectors. Biphenyl is an excellent chromosphore and its metal complexes show strong light emitting properties and long fluorescence life times. Further biphenyl based compounds are useful for redox and fluorescent sensors [1–3]. Most of the chalcones and their derivatives find useful in medical therapy, optical materials and polymeric UVabsorption filters [4]. These are precursors of various naturally occurring pigments [5]. Chalcones separated by bichromophoric moieties such as vinyl chains and carbonyl group were found to be effective photosensitive materials [6,7]. Several synthetic chalcones were reported as antineoplastic agents [8–10] as well as active against malaria, cardiovascular diseases and tuberculosis [11–14]. In this present study, we report the synthesis of novel
biphenyl based acrylate and methacrylate, which has excellent fluorescent property. Their structures were characterized using modern NMR spectroscopy 2D techniques like 1 H–1 H COSY, 1 H–13 C HSQC and 1 H–13 C HMBC. 2. Experimental 2.1. Materials and methods Bi-phenyl, 4-hydroxy benzaldehyde, acetyl chloride, aluminium trichloride, nitrobenzene, potassium hydroxide, triethylamine, ethylmethylketone, acryloyl chloride and methacryloyl chloride were purchased from Merck, and used without further purification. Solvents were purified and dried in accordance with the standard procedure [15]. 2.2. Physical measurements
General structure of compounds ACH (R = H) and MCH (R = CH3) (Numbering is given for better understanding in discussions)
∗ Corresponding author. Tel.: +91 44 22358660. E-mail address: [email protected] (K. Subramanian). 1386-1425/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.saa.2011.05.105
The infrared spectra were recorded using Perkin Elmer spectrum one instrument in the frequency range 4000–450 cm−1 , using KBr pellet method. NMR spectra were recorded using BRUKER 500 MHz AVANCE III instrument using CDCl3 as solvent, with TMS as an internal standard. The DEPT135 spectrum was recorded in standard manner = 135 pulse program, 2D techniques 1 H–1 H COSY, geHSQC and ge-HMBC spectra were recorded by using the standard Bruker pulse programs. The electronic spectra was recorded by UV1601 Shimadzu UV-Visible spectrophotometer in different solvents in the range of electronic absorbance between 200 and 800 nm. The fluorescence emission spectra were recorded using Perkin Elmer LS55 fluorescence spectrophotometer, using the excitation wavelength of the respective absorption maxima for different solvents.
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2.3. Synthesis 2.3.1. 4-Acetyl biphenyl (AB) Acetyl biphenyl was prepared as described in the literature [16]. Anhydrous aluminium trichloride (3.24 mmol) is added with 60 ml of nitrobenzene at ambient temperature under nitrogen atmosphere. To the above mixture, biphenyl (3.24 mmol) was added slowly with constant stirring followed by drop wise addition of acetyl chloride (3.24 mmol) at 0 ◦ C and the stirring was continued for 4 h. The reaction mixture was neutralized with sodium bicarbonate solution and extracted with ethyl acetate. The organic phase was washed with brine solution, and dried over anhydrous sodium sulphate. Volatiles were removed through vaccum and nitro benzene was removed by vaccum distillation. The residue was recrystalised using ethanol. Compound obtained as gray color solid Yield: 70%. m.p.: 118 ◦ C. 1 H NMR (500 MHz, CDCl3 ) ı ppm 2.66 (s, 3H), 7.43 (t, J = 7.55 Hz, 1H), 7.50 (t, J = 7.33 Hz, 2H), 7.66 (d, J = 8.20 Hz, 2H), 7.71 (d, J = 8.37 Hz, 2H), 8.06 (d, J = 8.50 Hz, 2H). 13 C NMR (126 MHz, CDCl3 ) ı ppm 26.65, 127.23, 128.23, 128.96, 135.89, 139.90, 145.84, 197.76. IR (KBr, cm−1 ) 1670, 2915, 2999.
2.3.2. 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenol (HCH) 4-Acetyl biphenyl (10.2 mmol) in methanol (30 ml) with potassium hydroxide (0.0408 mol). To the above reaction mixture, 4-hydroxy benzaldehyde (10.2 mmol) in 10 ml of methanol was added drop wise with constant stirring at 60 ◦ C. The reaction mixture was refluxed for 24 h; it was neutralized with dilute hydrochloric acid and extracted using ethyl acetate. The organic layer was washed with brine solution, dried over anhydrous sodium sulphate. Volatiles were removed through vaccum and purified by column chromatography. Compound obtained as yellow solid Yield: 72%. m.p.: 203 ◦ C. 1 H NMR (500 MHz, CDCl3 ) ı ppm 6.92 (d, J = 8.50 Hz, 2H), 7.41 (t, J = 7.25 Hz, 1H), 7.48 (t, J = 7.57 Hz, 2H), 7.54 (d, J = 15.76 Hz, 1H) 7.64 (d, J = 7.26 Hz, 2H), 7.67–7.71 (d, J = 8.51 Hz, 2H), 7.73 (d, J = 8.51 Hz, 2H), 7.79–7.87 (d, J = 15.45 Hz, 1H), 8.10 (d, J = 8.51 Hz, 2H). 13 C NMR (126 MHz, CDCl3 ) ı ppm 116.33, 119.04, 127.38, 127.47, 128.79, 129.56, 131.30, 131.50, 137.30, 139.49, 144.69, 144.93, 160.65, 188.93. IR (KBr, cm−1 ) 1639, 1511, 2986, 3312.
2.3.3. 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenyl prop-2-enoate (ACH) 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenol (3.3 mmol) in 20 ml of ethyl methyl ketone with triethylamine (3.6 mmol). To the above mixture, acryloylchloride (3.3 mmol) was added drop wise at 0 ◦ C. The mixture was stirred for 24 h at room temperature and is washed with excess of water and extracted with dichloromethane. The organic layer was washed with brine solution and dried over anhydrous sodium sulphate. Volatiles were removed through vaccum and purified by column chromatography. Compound obtained as pale yellow solid Yield: 79%. m.p.: 124 ◦ C. 1 H NMR (500 MHz, CDCl3 ) ı ppm 6.06 (t, J = 10.5 Hz, 1H unsaturated proton), 6.36 (dd, J = 17.5 Hz, 10.5 Hz, 1H unsaturated proton), 6.66 (dd, J = 17.5 Hz, 5 Hz, 1H unsaturated proton), 7.24 (d, J = 8.74 Hz, 2H), 7.43 (t, J = 7.43 Hz, 1H), 7.50 (t, J = 7.21 Hz, 2H), 7.58 (d, J = 15.73 Hz,1H), 7.67 (d, J = 7.43 Hz, 2H), 7.68 (d, J = 8.56 Hz, 2H), 7.75 (d, J = 8.03 Hz, 2H), 7.84 (d, J = 15.69 Hz, 1H), 8.12 (d, J = 8.38 Hz, 2H). 13 C NMR (126 MHz, CDCl3 ) ı ppm 122.18, 122.33, 127.32, 127.36, 127.44, 128.24, 128.97, 129.14, 129.62, 131.23, 132.72, 136.84, 139.93, 143.65, 145.65, 152.25, 164.21, 189.86. IR (KBr, cm−1 ) 1504, 1284, 1700, 1754, 2926, 3045, 3060. Anal. Calcd for C24 H18 O3 (MW 354.13): C, 81.34; H, 5.12; O, 13.54. Found: C, 81.26; H, 5.17; O, 13.72.
1993
Table 1 Infrared spectral data (cm−1 ) for ACH and MCH. Vibrations
ACH
MCH
C O (˛-ˇ-unsaturated) C O (aromatic ester) C–O (stretching) C C (˛-ˇ-unsaturated) C C (stretching) C–H (aliphatic methyl) stretching C–H (aromatic) C C (bending vibration) C–H (aliphatic methyl) bending
1700(s) 1754(s) 1284(s) 3045(w) 3060(w)
1659(s) 1726(s) 1318(s) 3042(s) 3058(w) 2853(w) 2926(w) 1504(w) 1416(w)
2926(w) 1504(w)
(s) – Strong; (w) – weak.
2.3.4. 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenyl 2-methylprop-2-enoate (MCH) 4-[(1E)-3-(biphenyl-4-yl)buta-1,3-dien-1-yl]phenol (3.3 mmol) in 20 ml of ethylmethylketone with triethylamine (3.6 mmol). To the above mixture, methacryloylchloride (3.3 mmol) was added drop wise at 0 ◦ C. The mixture was stirred 24 h at room temperature, washed with excess of water and extracted using dichloromethane. The organic layer was washed with brine solution dried over anhydrous sodium sulphate. Volatiles were removed through vaccum and purified by column chromatography. Compound obtained as pale yellow solid Yield: 78%. m.p.: 124 ◦ C. 1 H NMR (500 MHz, CDCl3 ) ı ppm 2.08 (s, 3H) 5.79 (s, 1H unsaturated proton), 6.37 (s, 1H unsaturated proton), 7.21 (d, J = 8.51 Hz, 2H), 7.41 (t, J = 7.25 Hz, 1H), 7.48 (t, J = 7.57 Hz, 2H), 7.54 (d, J = 15.76 Hz,1H), 7.64 (d, J = 7.26 Hz, 2H), 7.67–7.71 (d, J = 8.51 Hz, 2H), 7.73 (d, J = 8.51 Hz, 2H), 7.79–7.87 (d, J = 15.45 Hz, 1H), 8.10 (d, J = 8.51 Hz, 2H); 13 C NMR 126 MHz, CDCl3 ) ı ppm 13.37, 122.08, 122.29, 127.31, 127.33, 127.75, 128.25, 128.99, 129.16, 129.64, 132.58, 135.66, 136.84, 139.93, 143.49, 145.63, 152.63, 165.56, 189.90. IR (KBr, cm−1 ) 1318, 1416, 1504, 1659, 1726, 2853, 2926, 3042, 3058. Anal. Calcd for C25 H20 O3 (MW 368.14): C, 81.50; H, 5.47; O, 13.03. Found: C, 81.46; H, 5.54; O, 13.17. 3. Results and discussion The compounds of ACH and MCH were pale yellow powder; the analytical data for the complexes were in good agreement with the above molecular formula. The compound HCH having hydroxyl group was confirmed by spectral data. The preparation of compound HCH was achieved by Aldol condensation reaction of compound AB and 4-hydroxy benzaldehyde in the presence of a strong base like KOH as catalyst. Compounds ACH and MCH were synthesized by esterification reaction of compound HCH and corresponding acid chlorides in the presence of triethylamine. 3.1. Solubility Compounds ACH and MCH were found to be soluble in polar aprotic solvents like dimethyl sulfoxide, dimethylformamide, acetonitrile, dichloromethane, tetrahydrofuron, ethyl acetate, acetone and in non-polar solvent like chloroform. But the compounds were sparingly soluble in polar protic solvents like ethanol, methanol and in non-polar solvents like benzene. Compounds were completely insoluble in water. 3.2. IR spectra Generally ˛-ˇ-unsaturated esters show carbonyl stretching frequency at 1659 cm−1 but the compound MCH showed stretching vibration at 1700 cm−1 due to inductive effect of the methyl group. Compounds ACH and MCH showed aromatic stretching at 2926 cm−1 . The aliphatic methyl C–H stretching of compound
1994
R. Baskar, K. Subramanian / Spectrochimica Acta Part A 79 (2011) 1992–1997
Table 2 1 H and 13 C NMR data, 1 H–1 H COSY, 1 H–13 C HSQC and 1 H–13 C HMBC correlations of MCH. Carbon number
C1 C2 C2 C3 C4 C5,C5 C6,C6 C7 C8 C9 C10 C11 C12,12 C13,C13 C14 C15 C16,C16 C17,C17 C18
1
Chemical shift (ppm) ıH
ıC
Ha 5.83 (1H, s) Hb 6.84 (1H, s) – 2.03(3H, s) – – 7.21 (d, J = 8.51 Hz, 2H) 7.67–7.71 (d, J = 8.51 Hz, 2H) – 7.79–7.87 (d, J = 15.45 Hz, 1H) 7.54 (d, J = 15.76 Hz,1H) – – 8.10 (d, J = 8.51 Hz, 2H) 7.73 (d, J = 8.51 Hz, 2H) – – 7.64 (d, J = 7.26 Hz, 2H) 7.49 (2 H, t, J = 7.09 Hz) 7.41 (t, J = 7.25 Hz, 1H)
127.75 135.66 18.37 165.56 152.63 122.29 129.64 132.58 143.49 122.08 189.90 136.84 129.16 127.33 145.63 139.93 127.31 128.99 128.25
H–1 H COSY
H–13 C HSQC
1
1
H–13 C HMBC
( J)
( J)
(3 J)
H2
127.75
135.66(C2)
165.56(C3) 18.37(C2 )
– Ha , Hb
– 18.37 – – 122.29 129.64 – 143.49 122.08 – – 129.16 127.33 – – 127.31 128.99 128.25
135.66(C2)
165.56(C3) 127.75(C1)
152.63(C4) 132.58(C7)
132.58(C7) 152.63(C4) 143.49(C8)
132.58(C7) 122.08(C9) 189.90(C10)
129.64(C6) 189.90(C10) 132.58(C7)
127.33(13) 129.16(C12)
145.63(C14) 189.90(C10) 136.84(C11) 139.93(C15)
128.99(C17) 127.31(C16)128.28(C18) 128.99(C17)
145.63(C14)128.25(C18) 139.93(C15) 127.31(C16)
H6 H5 – H9 H8 – H13 H12
H17 H16
MCH appeared at 2853 cm−1 . The vibrational stretching frequency appeared at 1318 cm−1 was due to the presence of C–O–C linkage. The vinylic carbon shows vibration at 3050 cm−1 in compounds ACH and MCH. The vibration patterns are given in Table 1. The bands observed at region between 1000 and 800 cm−1 were the characteristic bands of C–H out of plane bending or vagging vibration of hydrogen atom attached to unsaturated carbons [20], relatively weaker absorption band at 1504 cm−1 is due to bending modes of ˛-ˇ-unsaturated carbons. Alkyl C–H bending vibration was observed at 1416 cm−1 in compound MCH, where as this vibration was not observed with ACH. 3.3. 1D and 2D NMR spectra In 1 H NMR spectrum of compounds ACH and MCH two doublets were observed at 7.54 (J = 15.76 Hz) and 7.81 (J = 15.45 Hz) which has been assigned to H8 and H9, the J value of these protons confirmed the product as a trans isomer (Figs. 3 and 4). All the compounds were exhibiting two triplets at 7.49 ppm and 7.41 ppm and were assigned to H17 and H18 respectively. The remaining 5
Fig. 1. Fluorescence spectra of ACH.
1
2
doublets were observed at 7.21 ppm, 7.69 ppm, 8.10 ppm, 7.73 ppm, 7.64 ppm, which had been assigned to H5, H6, H12, H13 and H16 respectively. The compound MCH showed one singlet at 2.03 ppm with three protons which corresponds to H2 methyl proton and two singlets were observed at 5.83 ppm and 6.84 ppm that corresponds to Ha and Hb. The singlet Hb is cis to carbonyl group which appeared in the down field region due to the presence of rich electron density around carbonyl oxygen when compared to Ha singlet. In the 13 C NMR spectra of the compound MCH, methyl (C2 ) carbon and olefinic (C1) carbon resonance were observed at 18.37 and 127.75 ppm respectively. 1 H–1 H COSY spectrum (Fig. 5) displayed scalar couplings for adjacent protons like H5 ↔ H6, H8 ↔ H9, H12 ↔ H13 and H16 ↔ H17. Further, the connection between these fourteen protons and its parent carbons namely C5 (122.29), C8 (143.49), C12 (129.16), C16 (127.31), C6 (129.64), C9 (122.08), C13 (127.33) and C17 (128.99), were confirmed by direct couplings in HSQC spectrum (Fig. 6). One triplet observed at ıH = 7.41 ppm is very closer to H17 its 1 H–1 H COSY scalar coupling correlation was very difficult, the 1 H–13 C correlation 1 H–13 C HSQC spectrum gives direct correlation to C18 (128.25). It was interesting to note that the
Fig. 2. Fluorescence spectra of MCH.
R. Baskar, K. Subramanian / Spectrochimica Acta Part A 79 (2011) 1992–1997
Fig. 3.
1
H NMR spectrum of ACH.
13 C NMR resonances for C2, C7 and C11 quaternary carbons were observed at 135.66 ppm, 132.58 ppm and 136.84 ppm respectively were obtained only in 1 H–13 C HMBC spectrum and not obtained in COSY and HSQC. The DEPT135 spectrum showed the disappearance of 13 C resonance at 135.66 ppm, 165.56 ppm, 152.63 ppm, 132.58 ppm, 189.90 ppm, 136.84 ppm, 145.63 ppm, 139.93 ppm, indicating that they were directly attached to proton bearing carbons. The higher chemical shift value observed at 189.90 ppm was due to C10 carbonyl carbon, and the next highest chemical shift was observed at 165.56 ppm was due to C3 carbonyl carbon, remaining were quaternary carbons, which was observed at stack plot of 13 C and DEPT spectrum. The HMBC spectrum was very useful for the assignment of six quaternary carbons. In HMBC correlation spectrum, the two olefinic protons (Ha and Hb ) showed the strong three bond coupling with C2 carbon, the H9 (7.54 ppm) and H13 (7.73) protons showed the three bond coupling with C7 (132.58) and C11 (136.84) respectively. The quaternary carbons C4 (152.63), C14 (145.63) and C15 (139.93) were well understood from HMBC
Fig. 4.
1
1995
correlation spectrum. 1 H, 13 C NMR data, 1 H–1 H COSY, 1 H–13 C HSQC and 1 H–13 C HMBC correlations are given in Table 2 (Fig. 7). 3.4. UV–vis spectra The absorption bands around 270–320 nm is characteristic peaks of chalcone moiety, the absorption maximum and extinction coefficient values are given in Table 3. The effect of solvent polarity is termed as solvatochromism [17]. The absorption maximum values (max ) for both compounds increase with increase in the solvent polarity. The compounds show bathochromic (red) shift at high by polar solvents. As a result, the compounds show → * transition in polar solvents. The compound ACH shows max at 330 nm and 338 nm in the solvents DMSO and ethanol respectively. The compound MCH shows max at 319 nm and 323 nm in DMSO and ethanol respectively. Because, the excited state is more dipolar than the ground state and the electronic transition energy decreases with increase in the polar solvent [18].
H NMR spectrum of MCH.
1996
R. Baskar, K. Subramanian / Spectrochimica Acta Part A 79 (2011) 1992–1997
Table 3 Electronic absorption and emission spectral data (bands) of ACH and MCH. Solvents
ACH
Ethanol DMSO Acetonitrile THF Dichloromethane Benzene
MCH
max (nm)
A
εmax (M−1 cm−1 )
em (nm)
F
max (nm)
A
εmax (M−1 cm−1 )
em (nm)
F
338 330 316 291 271 270
1.98 0.220 1.445 2.027 0.648 0.495
19,800 2,200 14,450 20,270 6,480 4,950
410 403 381 382 374 380
0.124 0.241 0.932 0.299 0.307 0.087
323 319 321 284 281 278
1.608 0.187 2.083 1.175 0.960 0,653
16,050 1,870 20,830 11,750 9,600 6,530
382 384 381 382 380 373
0.797 0.903 0.150 0.549 0.535 0.296
Fig. 5.
1
Fig. 7.
H–1 H COSY NMR spectrum of MCH.
1
H–13 C HMBC NMR spectrum of MCH.
3.5. Fluorescence spectra The emission maxima and its intensity in different solvents for compounds ACH and MCH are given in Table 3. em emission of compound ACH showed in polar solvents DMSO and ethanol were very high (403 nm, 410 nm) when compared to the non-polar solvent benzene(380 nm). The difference between the emission maxima and excitation maxima (Stokes shift) was higher in the polar solvents like DMSO and ethanol where as lesser in benzene Stokes shift [19]. Compound MCH also showed maximum intense emission and emission maxima in solvents DMSO and ethanol. Its emission maxima (em ) were 382 nm and 384 nm respectively. The emission spectra showed gradual red shift when the solvent polarity was changed from lower to higher. This is due to the fact that the excited state of the compounds is more stable than the ground state of high polar solvents when compared to that of the low polar solvents. The fluorescence emission spectra of compounds ACH and MCH are given in Figs. 1 and 2. 4. Conclusion
Fig. 6.
1
H–13 C HSQC NMR spectrum of MCH.
In this present study, we have synthesized a novel biphenyl based fluorescent compound, and their structure has been confirmed by different 1D and 2D NMR techniques. The compound ACH showed the em emission maximum in ethanol and DMSO, and the compound MCH also showed the maximum emission in ethanol and DMSO. The absorbance, emission, color, intensity of
R. Baskar, K. Subramanian / Spectrochimica Acta Part A 79 (2011) 1992–1997
fluorescence and solubility of both the compounds were investigated in different organic solvents.
[9]
Acknowledgements [10]
The authors are grateful to acknowledge SAIF, IIT-Madras for supporting in all the spectroscopic studies. We thank Dr. V. Kesavan, Department of Bio-technology, IIT-Madras for his support in this work.
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