Anomalously short fluorescence lifetimes in jet cooled 4-hydroxyindole. Evidence for excited state tautomerism and proton transfer in clusters

Jet cooled fluorescence lifetimes following excitation of S-1 origins have been measured for 4-hydroxyindole. The subnanosecond values obtained are anomalous compared to other substituted indoles, in particular 5-hydroxyindole. The short lifetimes are most likely related to excited state tautomerism in the bare 4-hydroxyindole. It was further found that one solvent molecule addition of triethylamine to 4-hydroxyindole is sufficient to induce excited state proton transfer, to a significantly greater extent than with 5-hydroxyindole.