Photophysical Properties and Excited‐State Dynamics of Luminescent N , O ‐Chelated Benzimidazole‐Based Boron Complexes

Luminescent N , O ‐chelated boron complexes are promising fluorescent materials owing to their rigid molecular structures and favorable photophysical properties. In this study, a series of luminescent N , O ‐chelated benzimidazole‐based boron complexes were synthesized, and their photophysical properties and excited‐state dynamics were systematically investigated by steady‐state and time‐resolved spectroscopic studies, supported by theoretical calculations. The complexes exhibited bright blue fluorescence with photoluminescence quantum yields of up to 0.76, whereas their absorption and emission properties were only slightly affected by the electronic nature of the boron‐bound aryl substituents. The calculations revealed that the lowest‐energy absorption originates predominantly from the HOMO→LUMO transition, while transient absorption spectroscopy provided insight into the excited‐state relaxation pathway. Representative complex 2a exhibited low cytotoxicity and preferential mitochondrial localization, suggesting its potential as a fluorescent probe for mitochondrial imaging.