Structure-property investigation of aminonaphthalene-based hemicyanine dyes for high-performance mitochondrial...

A series of aminonaphthalene-based hemicyanine probes (NI1-NI7) was developed through systematic modulation of amino substituents and the push-pull electronic framework to establish structure-property relationships for mitochondrial imaging. The structural variations effectively regulate intramolecular charge transfer processes, enabling tunable optical properties with absorption/emission maxima ranging from 560 to 690 nm and 647-742 nm, respectively. These probes exhibit large Stokes shifts (up to 120 nm), high molar absorptivity (up to 2.17 × 10⁴ M^-1 cm^-1), and high fluorescence quantum yields (up to 55.3%). Although the calculated HOMO-LUMO energy gaps remain relatively similar, molecular rigidification and electronic modulation significantly influence viscosity responsiveness, chemical stability, and cytocompatibility. Confocal laser scanning microscopy experiments demonstrate that all investigated probes possess efficient mitochondrial localization, with Pearson correlation coefficients of 0.89-0.94 from co-localization with MitoTracker Green. Among them, NI7 exhibits the most favorable balance of long-wavelength emission, viscosity responsiveness, mitochondrial targeting capability (PC = 0.94), and low cytotoxicity, enabling effective mitochondrial imaging at low concentration of 1 μM. This work establishes a clear structure-property-function relationship within aminonaphthalene-based hemicyanine fluorophores and provides a rational strategy for developing organelle-targeted fluorescent probes with tunable optical properties and biological imaging potential.