Photoinduced double proton transfer in water complexes of 1H-pyrrolo[3,2-h]quinoline and dipyrido[2,3-a:3′,2′-i]carbazole

Dual fluorescence is observed in water and water-containing solutions of 1H-pyrrolo[3,2-h]quinoline and dipyrido[2,3-a:3′,2′-i]carbazole. The low energy band is assigned to a product of excited state double proton transfer reaction, occurring in cyclic 1:1 complexes with water. Such complexes constitute only a small fraction of the ground state population. The majority of water complexes are not prone to phototautomerization, but are deactivated via a process that is not efficient in a non-hydrogen-bonded chromophore.