Electronic Structures and Photophysical Properties of Hydroxyl-Substituted ۱,۳-Bis(phenyl)triazenes: A DFT/TDDFT Analysis

Electronic structure and the nature of electronic excited states dictates the photophysical properties of the π-conjugated organic molecules and their utility in light-harvesting, sensing, and nonlinear optics. Substituted ۱,۳-bis(phenyl)triazenes with electron donor or acceptor functional groups exhibit unique photophysical properties due to their charge-transfer character. In this research work, hydroxyl (–OH) substituted ۱,۳-bis(phenyl)triazene derivatives are studied by density functional theory (DFT) and time-dependent DFT (TD-DFT) method at the B۳LYP/۶-۳۱۱G(d,p) level of theory. Molecular structures of the ground state (S۰) free gaseous ۱-(۲-hydroxyphenyl)-۳-phenyltriazene (۱), ۱-(۳-hydroxyphenyl)-۳-phenyltriazene (۲) and ۱-(۴-hydroxyphenyl)-۳-phenyltriazene (۳) were optimized, respectively, by DFT method. Also, the molecular structure of the first electronic excited state (S۱) of ۱-(۲-hydroxyphenyl)-۳-phenyltriazene (۲) was optimized by TD-DFT method in free gaseous state. The thermodynamic properties, electronic structures, electronic spectra and excited-state dynamics of the molecules were studied. The calculated HOMO-LUMO gap for ۱, ۲ and ۳ is ۳.۷۰, ۳.۹۱ and ۳.۸۲ eV, respectively. The optimized gaseous molecular structures of the compounds in the ground electronic state are planar. In the first excited state, in free gaseous ۲, the ۲-hydroxyphenyl group is rotated over the N-C bond and the dihedral C-N-N=N angle is ۸۷.۵۱°. In the calculated electronic absorption spectra of the compounds, the lowest energy electronic absorption band is due to the HOMO (π) to LUMO (π*) electron transfer. The effect of substitution position on the electronic absorption bands is studied.

Keywords:

۱ , ۳-bis(phenyl)triazenes , Electronic Excited State , Electronic Spectra , TD-DFT