Photo-Switchable Boronic Acid Derived Salicylidenehydrazone Enabled by Photochromic Spirooxazine and Fulgide Moieties: Multiple Responses of Optical Absorption, Fluorescence Emission, and Quadratic Nonlinear Optics

A novel protocol of the boronic acid derived salicylidenehydrazone (BASHY) core being sandwiched by photochromic spirooxazine and fulgide moieties was proposed here to design multistate fluorescent photoswitches with variable nonlinear optical (NLO) responses. Systematic investigations of their optical absorption, fluorescence emission, and static first hyperpolarizabilities (β) were performed using density functional theory (DFT). It was found that the BASHY-based sandwiched series exhibited significant differences of absorption and emission properties among three photoisomers, which were essentially ascribed to the massive changes of corresponding electron transition characteristics quantified by hole–electron descriptors and visualized by electron density difference (EDD) plots. However, the isomerization of fulgide parts in the merocyanine (MC) form of spirooxazine failed to greatly shift maximum absorption/emission wavelengths, due to their high similarity of intrinsic transition features. Furthermor...