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 need to be carefully unveiled to controllably tailor the optoelectronic properties. We have synthesized two D-A conjugated organic fluorophores, TPA-SO and TPA-CO, with similar molecular skeletons based on sulfone- or carbonyl-containing polycyclic aromatic acceptors. Both TPA-SO and TPA-CO display obvious solvent polarity-dependent photophysical properties and large Stokes shift of over 100 nm for strong intramolecular charge transfer processes. Experimental evidence indicates that the sulfone group in TPA-SO merely serves as a strong electron-withdrawing unit. TPA-SO shows yellowish-green emission with a peak at 542 nm and an absolute photoluminescence quantum yield (PLQY) of 98 % in solution, whereas the carbonyl group in TPA-CO can act as both an electron-withdrawing unit and spin transition convertor, so TPA-CO displays red emission with a low absolute PLQY of 0.32 % in solution. Impressively, upon going from solution to aggregate state, TPA-SO nanoparticles keep a high PLQY of 9.5 % and moderate biocompatibility, thus they are good nano-agents for cellular fluorescence imaging. The results reveal that the inherent acceptor characteristic acts as a crucial effect in the photophysical properties and applications of the organic fluorophores. Sulfone or carbonyl-based acceptor units were used to construct donor-acceptor conjugate organic fluorophores. Both TPA-SO and TPA-CO have solvent polarity-dependent photophysical properties for strong intramolecular charge transfer. As sulfone has weak intersystem crossing ability, TPA-SO has high fluorescence efficiency in solution and nanoparticles, and is a promising fluorescence dye.+image

Automated summary

In this study, two D-A conjugated organic fluorophores based on sulfone or carbonyl-based acceptor units were synthesized. These fluorophores showed solvent polarity-dependent photophysical properties, with high fluorescence efficiency suitable for cellular fluorescence imaging.