Excitation and emission properties of Zn(II) Schiff base complex by combined crystallographic, spectroscopic and DFT studies

The structure and photophysical properties of the Zn(II) complex with the novel fluorescent Schiff base ligand L: (E)-N′-((2-hydroxynaphthalen-1-yl) ethylene)acetohydrazide have been investigated. X-ray crystallography has proved the neutral, mononuclear complex: [ZnL₂]·H₂O·DMF, ZnL. The crystal packing proves intramolecular-interactions between the alternating naphthalene rings. Photophysical measurements of the complex in solvents of varying polarity (DCM, THF and DMSO) provide evidence for the formation of molecular aggregates in non-polar solvents that enhance the energy of the S₀-S₁ level. In the solid states, the complex exhibits unusual blue-shifted emission with respect to the ligand, due to excited state intermolecular proton transfer (ESIPT) within the ZnL molecules in the lattice. The experimental measurements are also complimented by DFT and TD-DFT calculations in the gas-phase and solution states.