A novel hetarylazoindole dye, 1,2-dimethyl-3-(pyridin-3-yldiazenyl)-1H-indole (DMPI) was synthesized by coupling 1,2-dimethylindole with diazotized 3-aminopyridine. The dye was characterized by FT-IR. FT-Raman, UV vis, H-1 NMR, C-13 NMR and X-ray diffraction techniques. The structure of the dye was determined by X-ray single crystal diffraction method. The molecular geometry, Gauge including atomic orbital (CIAO) H-1- and C-13 NMR chemical shift values and vibrational frequencies of DMPI molecule in the ground state were calculated by using the density functional theory (DFT). The theoretical electronic absorption spectra were calculated using time-dependent density functional theory (TD-DFT). The total energy distributions (TED) of the vibrational modes were calculated by using scaled quantum mechanical (SQM) analysis. (C) 2011 Elsevier B.V. All rights reserved.