Phosphine-based push-pull AIE fluorophores: Synthesis, photophysical properties, and TD-DFT studies

Herein, we report the design and characterization of a novel series of four push-pull fluorophores using diphenylphosphino as an electron-donating terminal group (P-chromophores). The spectroscopic properties in solution, the aggregation-induced emission (AIE) properties, as well as the emission properties in the solid state were studied and compared with those of the diphenylamino-analogues (N-chromophores). Comparative analysis of the crystalline structures coupled with density functional theory calculations revealed that the diphenylphosphino group adopts a pyramidal geometry, whereas a trigonal planar configuration around the N-center is observed for the diphenylamino group. Consequently, the phosphorous lone pair is localized on the upper side of the average chromophore plan and considerable geometrical change of the P-center can occur between the ground state and the first excited state, explaining the much larger Stokes shift observed (10 000 cm-1) for the Pchromophores compared to the N-analogues.