Résumé
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 P-chromophores compared to the N-analogues.
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•Push-pull dyes with a λ3σ3 diphenylphosphino electro-donor group were studied (P-dyes).•The weaker electro-donor character of P compared to N cause a blue-shift in the optical properties.•P-dyes showed solid-state emission with much larger Stokes shift than N-dyes.•P-centers adopt a trigonal pyramidal geometry whereas the N-centers are strictly trigonal planar.•The larger Stokes shift is due to bigger geometrical change of the donor P-atom between ground and first excited state.