Synthesis, photophysical characterization, CASSCF/CASPT2 calculations and CT-DNA interaction study of amino and azido benzazole analogues

Abstract

This work describes the synthesis and photophysical investigation of amino and azido benzazoles. The amino derivatives were obtained by condensation reaction between ortho-substituted anilines and p-aminobenzoic in polyphosphoric acid. The respective azides were synthesized by reaction of diazonium salts from the previously prepared amines with sodium azide. These compounds present absorption maxima in the UV-A region, nm ascribed to fully spin and symmetry electronic transitions. All compounds presented a main fluorescence emission in the UV-A to the violet region with a relatively large Stokes shift. The latter related to a solvent dependence. The amino derivatives presented higher values to the fluorescence quantum yields in despite of the azido analogues. DFT, TD-DFT and multiconfigurational calculations (SA-CASSCF and MS-CASPT2) were performed in order to investigate the photophysical features of these molecules, mainly on the azide derivatives, where the main interest was the investigation of the intrinsic fluorescence quenching present in these compounds. In this sense, it was observed that the weak fluorescence emission observed in the azide compounds could be related to the dissociative character of the S1 state, which reaches a conical intersection point between S1/S0 states, and through this point, goes back to the ground state by a nonradioactive decay. In addition, the DNA binding assays by UV–Vis absorption and fluorescence emission methodologies indicated that the benzazoles presented strong interaction with CT-DNA, which could be attributed to π-stacking and/or intermolecular hydrogen-bonding. Docking was also performed to better understand the observed interaction.