Subtle Structural Changes of Dyes Lead to Distinctly Different Fluorescent Behaviors in Cellular Context: The Role of G-Quadruplex DNA Interaction Using Coumarin-Quinazolinone Conjugates as a Case Study.

Fluorogenic organic materials have gained tremendous attention due to their unique properties. However, only a few of them are suitable for bioimaging. Their different behaviors in organic and cellular environments hinder their application in bioimaging. Thus understanding the photoluminescent behaviors of organic materials in a cellular context is particularly important for their rational design. Herein, we describe two coumarin-quinazolinone conjugates: and . The high structure similarity makes them possess similar physical and photophysical properties, including bright fluorescence ascribed to the monomer forms in organic solvents and aggregation-caused quenching (ACQ) effect due to self-assembly aggregation in aqueous solution. However, they behave quite differently in cellular context: that is, exhibits bright fluorescence in living cells, while the fluorescence of is almost undetectable. The different performance between and in living cells is attributed to their different scenario in G-quadruplex (G4) DNA interaction. selectively binds with G4 DNA to recover its fluorescence aggregation-disaggregation switching in living cells, while remained in the aggregate form due to its poor interplay with G4 DNA. Furthermore, is applied as a two-photon fluorescent dye, and its photoswitchable fluorescence capability is exploited for super-resolution imaging of the specific mitochondrial structure in living cells the STORM technique.