Exploring 4-Amino-1,8-Naphthalimides: Lifetime-Based Sensing of Chemical Micro-Environments.

Fluorescence lifetime offers a powerful approach to probe chemical microenvironments in biological systems, yet suitable fluorophores remain limited. Here, we report the synthesis and photophysical characterisation of a library of fifteen 4-amino-substituted 1,8-naphthalimides, incorporating diverse aliphatic and aromatic amines. These compounds exhibit strong solvatochromism and varied fluorescence lifetimes in response to polarity and viscosity. Notably, compound 13 demonstrates high brightness and pronounced fluorescence lifetime sensitivity to polarity, while compound 17 shows strong viscosity-dependent lifetime changes. We apply compound 13 to rat serum samples, revealing significant differences in fluorescence lifetime between healthy and acute pancreatitis conditions, consistent with polarity changes. In contrast, compound 17 showed no lifetime variation, suggesting limited viscosity changes in serum. These findings highlight the potential of 4-amino-1,8-naphthalimides as environment-sensitive probes, particularly for polarity sensing in complex biological samples. More generally, this work expands the photophysical understanding of naphthalimide derivatives and supports their application in fluorescence lifetime-based sensing of disease-related microenvironmental changes.