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.