Photophysical and computational studies of novel heterocyclic imidazole derivatives containing trifluoromethyl group substituent

Phenanthrimidazole ligands with potential electron withdrawing trifluoromethyl substituent have been synthesized and characterized using IR, mass and NMR spectral studies. The effect of solvent on their absorption and emission have been analysed in detail by Kamlet–Taft Catalan approach. The introduction of trifluoromethyl substituent results in a significant blue shift in emission when compared to its parent compound. This is due to the presence of the electron withdrawing trifluoromethyl moiety which changes the π–π conjugation of the cyclometalated ligand and lowers the triplet energy level, thus lowering the lowest unoccupied molecular orbital (LUMO) level. The optimized bond lengths, bond angles and dihedral angles calculated by DFT/B3LYP/6–31G (d,p) method are found to be slightly higher than that of XRD values of its parent compound. NBO, NLO, MEP and HOMO–LUMO energy analysis have been carried out by DFT method. This shows that the synthesized imidazole derivatives possess non-linear optical (NLO) behavior. In addition to these, calculations regarding the chemical potential, hardness and electrophilicity index have also been done.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Effect of trifluoromethyl group substituent in UV–vis and emission studies. ► A multi-component linear regression analysis to correlate UV and emission results. ► DFT calculation of dipole moment, hyperpolarizability, donor–acceptor interactions. ► PES diagram, MEP and electronic properties studied using Gaussian-03. ► Bar diagram: the charge distribution calculated by NLO and NBO analysis.