Sulfone/Carbonyl-Based Donor-Acceptor Fluorescent Dyes: Synthesis, Structures, Photophysical Properties and Cell Imaging.

Electron-accepting units play vital roles in constructing donor-acceptor (D-A) conjugated organic optoelectronic materials, the electronic structures and functions of the acceptors are needed to carefully unveil to controllably tailor the optoelectronic properties. Herein, we synthesized two D-A conjugated organic fluorophores (named TPA-SO and TPA-CO) with similar molecular skeletons based on sulfone or carbonyl contained polycyclic aromatic acceptors. For strong intramolecular charge transfer processes, both TPA-SO and TPA-CO display obvious solvent polarity-dependent photophysical properties and large Stokes shift of over 100 nm. The experimental evidences indicate sulfone group in TPA-SO merely serves as a strong electron-withdrawing unit, and TPA-SO shows yellowish-green emission with an emission peak at 542 nm and absolute photoluminescence quantum yield (PLQY) of 98% in solution, while the carbonyl group in TPA-CO can act as both electron-withdrawing unit and spin transition convertor, so TPA-CO displays red emission with a low absolute PLQY of 0.32% in solution. Impressively, from solution to aggregate state, TPA-SO nanoparticles keep high PLQY of 9.5% and good biocompatibility, which are good nanoprobes for cellular fluorescence imaging. The results reveal that the inherent characteristic of acceptors acts as a crucial effect in the photophysical properties and applications of the organic fluorophores.