Variation of the Emission Efficiency and Wavelength from Fluorescent Zinc Salen Complexes upon Systematic Structural Modifications.

Understanding the photophysical properties of metal salen complexes is not straightforward because the emission efficiency is altered irregularly upon structural modifications. The present study prepared zinc salen complexes with systematic structural variations to pinpoint critical factors to determine the emission efficiency. One of the important experimental observations is the regiochemistry of a phenolate substituent affecting emission efficiency from a salicylidene fluorophore, which is nicely assigned as arising from the photoexcited electronic structure of metal salen complexes. Another significant finding is the thermal fluctuation of a salen ligand arising from the mismatched ligand-metal interaction, which has a significant impact on fluorescence lifetime. The present study sheds light on hidden factors that alter photophysical properties of a metal salen complex, which provide valuable insights into designing new photoactive salen ligands.