Study of fluorescence properties of several 4-acyl pyrazolone derivatives and their Zn (II) complexes

Fluorescence properties of four 4-acyl pyrazolone derivatives (H2L1 = N-(1,3-diphenyl-4-propylene-5-pyrazolone)-salicylidene hydrazone (1), H2L2 = N-(1,3-diphenyl-4-ethylene-5-pyrazolone)-salicylidene hydrazone (2), H2L3 = N-(1,3-diphenyl-4-benzylidene-5-pyrazolone)-salicylidene hydrazone (3), H2L4 = N-(1,3-diphenyl-4-phenylethylene-5-pyrazolone)-salicylidene hydrazone (4), and their Zn (II) complexes: (Zn(H2L1)2 (5), Zn(H2L2)2·3CH3OH (6), Zn(H2L3)2·2CH3OH (7), and Zn4(H2L4)4 (8)) were studied at room temperature. It was revealed that these compounds show different fluorescence properties both in the solid state and in solution. Density functional theory (DFT) calculations on ligands 1–4 were also performed to further understand their emission properties. The calculation results indicate that the energy gaps between the highest occupied molecular orbitals (HOMOs) and the lowest unoccupied molecular orbitals (LUMOs) of these ligands are in the following order 1 > 2 > 3, which is consistent with the redshift of the emission spectra.