R. Kang, L. Talamini, E. D'Este, B. Martins Estevao, L. De Cola, W. Klopper, F. Biedermann, Chem. Sci. 2021, 12, 1392-1397.

DOI: 10.1039/D0SC05557C


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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 (pKa2 ? 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 via coupled-cluster calculations, making HINA an interesting model for future method development.