Discovery of a size-record breaking green-emissive fluorophore: small, smaller, HINA

Abstract

Astonishingly, 3-hydroxyisonicotinealdehyde (HINA) is despite its small size a green-emitting push-pull fluorophore in water (QY of 15%) and shows ratiometric emission response to biological relevant pH differences (p<i>K</i> _a2 ∼ 7.1). Moreover, HINA is the first small-molecule fluorophore reported that possesses three distinctly emissive protonation states. This fluorophore can be used in combination with metal complexes for fluorescent-based cysteine detection in aqueous media, and is readily taken up by cells. The theoretical description of HINA's photophysics remains challenging, even when computing Franck-Condon profiles <i>via</i> coupled-cluster calculations, making HINA an interesting model for future method development.