Photophysical and excited-state intramolecular proton transfer of 2-(1-(3,5-dimethylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenol: DFT analysis

•Non-viability of ground state electron transfer was explained by HOMO–LUMO analysis.•The strong IMHB interaction is substantiated under the provision of NBO and AIM analysis.•The results of AIM calculation reinforce the presence of strong IMHB.

Fluorescent phenenthrimidazole derivatives have been synthesized and characterized by 1H, 13C NMR and mass spectral analyses. Synthesized compounds have been. The solvent effect on the absorption and fluorescence bands has been analyzed and supplement by computational studies. Phenenthrimidazole containing hydroxy group shows a single prominent absorption and emission in polar solvents and dual emission in non-polar solvents due to excited state intramolecular proton transfer (ESIPT). The ESIPT of 2-(1-(3,5-dimethylphenyl)-1H-phenanthro[9,10-d]imidazol-2-yl)phenol was cross validated by the analysis of optimized geometry parameters, potential energy surface (PES), mulliken’s charge distribution on the heavy atoms and molecular orbitals of its tautomers. Nonviability of ground state electron transfer was explained by HOMO–LUMO analysis. The intramolecular hydrogen bonding (IMHB) interaction has been explored by the calculation of electron density ρ(r) and the Laplacian Δ2ρ(r) at the bond critical point (BCP) using atoms-in-molecule (AIM) method and by calculation of hyper conjugative interaction between N17 lone pair and σ*(O53⋯H54) using natural bond orbital (NBO) analysis.

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