First step toward a universal fluorescent probe: unravelling the photodynamics of an amino-maleimide fluorophore

Continuous advancements in biophysics and medicine at the molecular level make the requirements to image structure–function processes in living cells ever more acute. While fluorophores such as the green fluorescent protein have proven instrumental toward such efforts, the advent of nondiffraction limited microscopy limits the utility of such fluorescent tags. Monoaminomaleimides are small, single molecule fluorophores that have been shown to possess stark variations in their emission spectra in different solvent environments, making them a potentially powerful tool for a myriad of applications. The ability to “autotune” fluorescence according to different media allows for a probe capable of working in all regions of a cell, or accurately characterizing the purity of an environment. In this work, we present ultrafast pump–probe studies of a model monoaminomaleimide, 1-methyl-3-(methylamino)-1H-pyrrole-2,5-dione, and demonstrate how fluorescence quenching in polar protic solvents is caused by electron driven proton transfer from the solvent to the fluorophore. Armed with this knowledge, the present study acts as a first step for the rational design of future maleimides, potentially moving toward creating a universal fluorophore with tunable efficiency, dependent on environment.