Structural isomerism engineering regulates molecular AIE behavior and application in visualizing endogenous hydrogen sulfide

Abstract

Hydrogen sulfide (H₂S) is a critical bioregulator implicated in numerous physiological and pathological processes, including cancer and neurodegenerative diseases. Overcoming the shortcomings of traditional analysis, fluorescent detection technology based on small molecules in real-time and in situ sensing H₂S has attracted attention. In this investigation, we developed a system of coumarin-based fluorophores tying aminopyridine via a dipolar imino-double bond. Their aggregation-induced emission (AIE) behaviors were further regulated through structural isomerism engineering. Thanks to restricting intramolecular motions and high molecular dipole moment, 2-amino-pyridyl substituted coumarin (CMR-o-Py) forms stable AIE nanoaggregates with higher bright fluorescence than the others. The CMR-o-Py nanoaggregates serve as probe sensing H₂S with a detection limit of 18.1 μM in the hydrophilic environment through Michael addition between imino-bond and sulfide ions. The 1:1 stoichiometrical binding energy constant between the probe and H2S is 5.68×10⁸ M^-1, and its half-time of the first-order binding reaction is estimated as 4.85 min. Moreover, CMR-o-Py, with excellent biocompatibility, makes it ideal as a sensor for endogenous H₂S in living cells and onion tissues, further highlighting its potential application in biological regions.