Bent Benzocoumarin Dyes that Fluoresce in Solution and in Solid State and Their Application to Bioimaging

Organic fluorophores are essential in microscopic imaging of biological systems. New fluorophores with distinct features are in demand for bioimaging. Herein we report new bent benzocoumarin dyes that are fluorescent both in solution and in the solid state. The latter property enables us to form fluorescent nanoparticles with a mean size of 120–157 nm or larger depending on conditions. Some of the new dyes provide bright fluorescent images in cell, with formation of particulate spots that persist even after several washout procedures, and, furthermore, in tissue under two‐photon excitation at 900 nm. Such dyes have potential for the development of fluorescent probes for enhanced cellular fluorescence. Twist and shout: A class of bent benzocoumarin dyes have been developed which emit in the solid state as well as in solution. Exploiting the fact that these dyes can form emissive particles in cells, further confocal and two‐photon microscopy studies have been conducted for selected cell and tissue samples that proved that the dyes are good tools for bioimaging applications.