Substituent effects on the ultraviolet absorption properties of stilbene compounds-Models for molecular cores of absorbents

Abstract

The effects of substituent X and Y on ultraviolet (UV) absorption properties of stilbene compounds XPhCHCHPhY (XSBY) were studied both experimentally and computationally from the viewpoint of UV maximum absorption wavelength (λ_max) and the corresponding energy (υ_max). In the studies, the contribution of substituents on υ_max shift was explored. The results show that with increase of electron withdrawing or electron donating ability of X or Y, there is an enhanced electron delocalization of XSBY that leads to bathochromic shift. Computational analyses based on density functional theory were conducted to elucidate the phenomena. It is disclosed that the υ_max values are significantly affected by the excited state, though the electronic effect of ground state cannot be ignored. Finally, on the basis of the respective influences of X and Y, a quantitative model, which was proved reliable by the leave-one-out method, was developed to scale the effects of terminal substituents on υ_max. According to the model, the effects of substituents X or Y exhibit almost the same action on υ_max owing to the symmetric skeleton of the XSBY compounds. The findings provide deep insight into the effects of terminal substituents on UV absorption properties of stilbene compounds, and the derived model enables practical expression of the relationship between substituents and UV absorption.

Keywords: Absorption spectra; Stilbene compounds; Substituent effects; Ultraviolet absorbents.