Architecting ultra-bright silanized carbon dots by alleviating the spin-orbit coupling effect: a specific fluorescent nanoprobe to label dead cells.

Through high temperature dehalogenation/polymerization process, a new class of green-emitting silanized carbon dots (Si-CDs) featuring ultrahigh photoluminescence quantum yield (PLQY) is developed. The mechanism of improving the PLQY of Si-CDs mainly includes two steps. Firstly, the dehalogenation process can alleviate the spin–orbit coupling (SOC) effect of heavy-atom-rich organic fluorophores with severe intersystem crossing through high temperature hydrothermal reaction, meanwhile the possibility of transition from excited state (S 1) to triplet state (T 1) in the Si-CDs is significantly reduced, thus enhancing the fluorescence intensity and prolong fluorescence lifetime of Si-CDs. Besides, multiple fluorescent emitters can be integrated into one nano dot to effectively enhance the emission intensity in a single nano dot level by cross-linking polymerization. Moreover, Si-CDs can be used as fluorescent nanoprobes, which can rapidly and universally label dead cells, thus fast discriminate live/dead cells. [Display omitted] • Ultrabright green Si-CDs with small size and robust photostability was obtained. • Enhanced the fluorescence intensity by alleviates the spin–orbit coupling effect. • Enhanced the emission intensity by integrating multiple emitters into one nanodot. • Si-CDs can be applied in fast discriminating live/dead cells. Developing high-performance carbon dots (CDs) with high photoluminescence quantum yield, excellent stability, and good biocompatibility as well as explore the related luminescence mechanism is still an urgent problem to be solved at present. Herein, we develop a new class of green-emitting silanized carbon dots (Si-CDs) featuring average size of ~ 2.8 nm, ultrahigh photoluminescence quantum yield of ~ 93%, robust photostability, and low cytotoxicity by high-temperature dehalogenation/polymerization process. Our experiments verify the dehalogenation process can alleviate the spin–orbit coupling (SOC) effect of heavy-atom-rich organic fluorophores with severe intersystem crossing through high-temperature hydrothermal reaction, meanwhile, the possibility of transition from the excited state (S 1) to triplet state (T 1) in the Si-CDs is significantly reduced, thus enhancing the fluorescence intensity and prolong fluorescent lifetime of Si-CDs. Besides, multiple fluorescent emitters can be integrated into one nanodot to effectively enhance the emission intensity by cross-linking polymerization. Owing to good optical properties of the obtained Si-CDs, when used as fluorescent nanoprobes, Si-CDs can rapidly and universally label dead bacteria, fungi, and mammalian cells, which can meet the needs of green fluorescent nanoprobes for specific imaging of dead cells, so as to fast discriminate live/dead cells. We believe that Si-CDs with excellent optical performance, ultrasmall particle size, and low cytotoxicity can be applied to the fields of biological imaging, optical devices, and anti-counterfeiting. [ABSTRACT FROM AUTHOR]