Examinations directed to characterization within the framework of spectroscopic and DFT approach on the structural isomer of the pyridine substituted thiazole

• Characterization of pyridine substituted thiazole by XRD, FT-IR, NMR techniques. • Photophysical properties with UV-Vis and fluorescence spectra. • Global and local reactivity descriptors based on the DFT approach. In the present paper, we reported the synthesis of two structural isomers of pyridine-substituted thiazole having heterocyclic moieties, characterized by XRD, FT-IR, NMR, UV-Vis and fluorescence techniques. Their molecular geometries and presence of hydrogen bond interactions were determined with single-crystal X-ray diffraction (XRD) analysis. The process steps of analyses performed with the theoretical approach were carried out with density functional theory (DFT), B3LYP functional and 6-311G(d,p) basis set. The parameters of molecular geometry, spectral vibrational modes base on potential energy distribution (PED) and 1 H and 13 C-NMR chemical shifts for the structures were evaluated comparatively with DFT results. To determine photophysical properties, absorption bands with the time-dependent DFT (TD-DFT) approach and spectral emission bands were examined. Frontier molecular orbitals (FMOs), global and local reactivity descriptors, atomic charge distributions based on Mulliken and Natural Population analysis (MPA and NPA) were utilized to specify the reactivity properties of the structures. Further, nonlinear optical (NLO) properties and some thermodynamic parameters were investigated at the same theoretical level. The results of these analyses show that most of the spectral parameters examined are sensitive to the position of the substituent and the pyridine substitution 4-position to thiazole structure exhibit chemically more reactive a profile than at 2-position.