Intermolecular excited state double proton transfer in dipyridocarbazole:alcohol complexes

Addition of alcohols to solutions of dipyrido[2,3-a:3',2'-i]carbazole leads to fluorescence quenching and to the appearance of a new, strongly red-shifted fluorescence band. This new band is interpreted in terms of excited state double proton transfer in dipyridocarbazole:alcohol complexes. This conclusion is supported by the results of transient picosecond absorption studies and the calculations performed for the intitial and tautomeric forms. Two different precursors of the tautomer are identified: in one of them, the reaction occurs through a barrier, while in the other, phototautomerization proceeds even at low temperatures.