Rational design of a diaminomaleonitrile-based mitochondria – targeted two-photon fluorescent probe for hypochlorite in vivo: Solvent-independent and high selectivity over Cu2+

Abstract

For the rational design of a solvent-independent diaminomaleonitrile (DAMN)-based fluorescent probe for monitoring ClO− selectively without the interference from Cu2+, a feasible strategy is to introduce the DAMN group into a sterically crowded π-conjugated framework. The addition of ClO− will recover the planarity of the molecule, change the D-π-A structure, and influence intramolecular charge transfer (ICT) efficiency in the sensing system. Inspired by this strategy, a DAMN-based Schiff base derivative (HCCN) was designed and synthesized to detect ClO− with a rapid response, a large Stokes shift and moderate two-photon excitation action cross-section. HCCN was highly selective for ClO− detection with no analyte interference (especially from Cu2+) in CH3CN/PBS and other mixed solvent systems. Density functional theory (DFT)/TDDFT calculations supported that the enhanced fluorescence signal of HCCN to ClO− was arisen mainly from the recovery of the planar structure and the accompanying enhancement of ICT efficiency in 4. A co-staining experiment of HCCN showed its high affinity towards intracellular mitochondria; subsequently, HCCN was successfully applied for two-photon bio-imaging of exogenous ClO− in fresh tissues and endogenous ClO−in vivo.