The Raman, SERS and computational studies of 3,5-dimethoxy-4-hydroxycinnamic acid and its silver complex.

Optimized chemical structure, Raman and SERS spectra of 3,5-dimethoxy-4-hydroxycinnamic acid (35D4HCA) molecule and its silver (Ag) complex were calculated using time-dependent density functional theory in conjunction with B3LYP functional and LANL2DZ/6-311 + G(d,p) basis sets. Moreover, excitation and HOMO-LUMO energies were computed by the same level of theory. Because of the fact that energy of excitation electronic transition depends on infinite lifetime approximation, Raman activities were calculated under this approximation. Normal Raman spectra and SERS spectra of 35D4HCA and its silver complex were obtained with different excitation laser frequencies such as 532 nm and 785 nm and so interaction between metal surface and 35D4HCA was examined using SERS spectra. Moreover, theoretical and experimental UV-VIS spectra in the water of 35D4HCA and its silver complex were obtained and transitions, wavelengths and energy values of samples were shown. H NMR experiment of 35D4HCA and its silver complex were performed and it was determined interaction between Ag atoms and 35D4HCA. In order to determine thermal properties of 35D4HCA and its silver complex, TG and DTA analysis were carried out. HOMO and LUMO energy levels corresponding to these energy values were determined and transitions between these levels were determined.