AYDINER/Turk J Chem
catalyst and also AcOH and concentrated HCl as decarboxylating agents. The second step was the formylation
of compound 1 at the 3-position of coumarin using Vilsmeier Haack reagent (POCl3 and DMF) in an inert
1
atmosphere. Yield: 82%; mp: 164 ◦ C (lit.: 168–170 ◦ C); H NMR (300 MHz, CDCl3)δ 9.90 (s, 1H), 7.64 (d,
J = 9.1, 1H), 6.85 (dd, J = 9.19 and 2.4 Hz, 1H), 6.61 (d, J = 2.3, 1H), 3.51 (q, J = 7.1, 4H), 1.17 (d, J =
7.0, 6H).
2.3. Synthesis of benzilmonohydrazone (3)
Compound 3 was synthesized by simple condensation between benzil (C) and hydrazine hydrate in ethanol
utilizing a reported method [21]. Yield: 95%; mp: 151 ◦ C (lit.: 151 ◦ C)
2.4. Synthesis of 7-(diethylamino)-3-((E)-(((E)-2-oxo-1,2-diphenylethylidene)hydrazono)methyl)-
2H-chromen-2-one (4)
Compound 4 was synthesized by mixing 7-(diethylamino)coumarin-3-aldehyde (2) (1 mmol, 245 mg) with
benzilmonohydrazone (3) (1 mmol, 224 mg) in 20 mL of ethanol and three drops of acetic acid. The mixture
was refluxed for 4 h, then cooled and filtered, and the dark orange solid was washed with ethanol. It was used
without any purification process. Yield: 65%; mp: 225–226 ◦ C. FT-IR (ATR, νmax , cm−1): 3063 (Ar-H);
1
2972 (R-H); 1713 (C=O); 1673 (C=O); 1615 (C=N). H-NMR (300 MHz, CDCl3) δ 8.79 (s, 1H), 7.95 (dd,
J = 8.9 and 2.4 Hz, 2H), 7.86 (s, 1H), 7.83 (dd, J = 8.3 and 1.7 Hz, 2H), 7.63–7.34 (m, 6H), 7.15 (d, J = 8.9
Hz, 1H), 6.53 (dd, J = 8.9 and 2.4 Hz, 1H), 6.43 (d, J = 2.3 Hz, 1H), 3.42 (q, J = 7.1 Hz, 4H), 1.24 (t, J =
13
7.2 Hz, 6H) (Figure 1).
C-APT (75 MHz, CDCl3): δ 197.9; 166.3; 161.5; 157.6; 157.3; 151.9; 141.4; 135.6;
133.8; 132.7; 131.3; 130.8; 129.2; 128.9; 128.8; 127.7; 112.8; 109.4; 108.6; 97.1; 45.0; 12.4 (Figure 2). HR-MS
+
(m/e) (M-H) : C28 H26 N3 O3 , calc.: 452.1974 ; found: 452.1983, [δm/m (ppm) = 1.99].
3. Results and discussion
3.1. Synthesis
Compound 4 was synthesized by the stepwise procedure demonstrated in Scheme 1. The reaction of 7-
(diethylamino)coumarin-3-aldehyde (2) with benzilmonohydrazone (3) in the presence of piperidine gave 7-
(diethylamino)-3-((E)-(((E)-2-oxo-1,2-diphenylethylidene)hydrazono)methyl)-2H-chromen-2-one (4). The struc-
1
13
ture of the compound was confirmed by FT-IR, H NMR,
C-APT NMR, and HR-MS techniques. The
compound was obtained with moderate yield (65%).
3.2. Photophysical properties
The UV-Vis spectral data of dye 4 were measured in different solvents with various polarities at room tem-
perature. Compound 4 is soluble in tetrahydrofuran (THF), dichloromethane (DCM), chloroform (Chl), and
dimethyl sulfoxide (DMSO), while it is sparingly soluble in protic polar solvents such as acetic acid (AcOH),
methanol (MeOH), and ethanol (EtOH) at 10 µM. Effects of solvent polarity on absorption and emission spectra
of the chemosensor were investigated and photographs of the color changes were taken under daylight and UV
light. The absorption coefficients (ε) were calculated according to the Beer–Lambert law and values are given
in Table 1. In Figure 3, normalized absorption and emission spectra of 4 in four selected solvents (THF, DCM,
Chl, and DMSO) can be seen. Chemosensor 4 showed red-shifted absorption with an increase in solvent polarity
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