Synthesis, characterization, DFT, and TD-DFT studies of (E)-5-((4,6-dichloro-1,3,5-triazin-2-yl)amino)-4-hydroxy-3-(phenyldiazenyl)naphthalene-2,7-diylbis(hydrogen sulfite)

In this study, (E)-5-((4,6-dichloro-1,3,5-triazin-2-yl)amino)-4-hydroxy-3-(phenyldiazenyl)naphthalene-2,7-diylbis(hydrogen sulfite), a cyanurated H-acid (CHA) azo dye, was synthesized and characterized using FT-IR spectrophotometer and GC-MS spectroscopy. A density functional theory (DFT) based B3LYP and CAM-B3LYP method with 6-311 + G (d,p) basis set analysis was computed for HOMO-LUMO, natural bonding orbitals (NBO), UV-Vis absorptions and excitation interactions, in order to understand its molecular orbital excitation properties. A low Energy gap (Eg) of 2.947 eV was obtained from the molecular orbital analysis, which showed that HOMO to LUMO transition is highly feasible; hence CHA is adequate for diverse electronic and optic applications. Studies of the first five excitations (S-0 -> S-1/S-2/S-3/S-4/S-5) of CHA revealed that S-0 -> S-1 and S-0 -> S-3 are pi -> pi* type local excitations distributed around the -N=N- group; S-0 -> S-2, a Rydberg type local excitation; S-0 -> S-4, a highly localized pi -> pi* excitation; while S-0 -> S-5 is an n -> pi* charge transfer from a benzene ring to -N=N- group. From NBO analysis, we obtained the various donor-acceptor orbital interactions contributing to the stabilization of the studied compound. Most significantly, some strong hyper-conjugations (n -> n*) within fragments, and non-bondingand anti-bonding intermolecular (n -> n*/pi* and pi -> n*/pi*) interactions were observed to contribute appreciable energies. This study is valuable for understanding the molecular properties of the azo dyes compounds and for synthesizing new ones in the future.