Optical properties of organic nonlinear optical crystal—A combined experimental and theoretical study

The optical properties of the synthesized imidazole derivative, 1-(4-methoxyphenyl)-4,5-diphenyl-2-styryl-1H-imidazole, has been studied both experimentally and theoretically. Fluorescence enhancement have been found in the presence of transition metal ions and this may result from the suppression of radiationless transitions from the n-π* state in the chemosensors. Quantum chemical calculations of heat of formation, optimized geometry, NLO, HOMO–LUMO, MEP and NBO analysis of 1-(4-methoxyphenyl)-4,5-diphenyl-2-styryl-1H-imidazole (mpdsi) have been carried out by using density functional theory (DFT/B3LYP) method with 6-31G(d,p) as basis set. This chromophore possess more appropriate ratio of off-diagonal versus diagonal β tensorial component (r = βxyy/βxxx = −0.002) which reflects the inplane non-linearity anisotropy. Since they have largest μβ0 value, the reported imidazole can be used as potential NLO material. The solvent effect on the absorption and fluorescence has been analyzed simultaneously.

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► Chemosensor: the enhancement of fluorescence during exposure to metal ions.
► Octupolar components: steric interaction must be reduced to obtain larger β0 values.
► NBO: intramolecular, hybridization and delocalization within the molecule.
► HOMO–LUMO: probable charge transfer (CD) taking place inside the chromophore.
► Bar diagram: the charge distribution was calculated by NBO and Mulliken methods.