Photoluminescence and Structure-property Relationships in Alkynyl-functionalized Ni(II) and Zn(II) Salicylaldimine Complexes.

Abstract

A series of alkynyl-functionalized salicylaldimine ligands bearing H, NO₂, and OCH₃ substituents and their corresponding complexes [Ni(L_1-3)] (1a-c) and Zn(L_1-3)] (2a-c) were synthesized and characterized by spectroscopic, thermal, electrochemical, and photophysical techniques. Metal coordination produced red-shifted absorption and emission bands and enhanced fluorescence relative to the free ligands. Among the investigated derivatives, the OCH₃-substituted complexes showed the highest emission intensity, lifetime, and quantum yield, consistent with the electron-donating nature of the substituent and the extended π-conjugated framework. The Ni(II) complexes exhibited substituent-dependent quasi-reversible redox behavior. All complexes showed moderate SHG activity, with only small variations among the different substituents. Overall, the results demonstrate systematic but relatively modest structure-property relationships, arising from the combined effects of metal coordination, π-conjugation, and ligand substituents on the photophysical, electrochemical, and nonlinear optical properties of the complexes, highlighting their promising their photonic and optoelectronic applications.