Self-quenching in the stepwise photocyclization of 1,4-bis(diphenylamino)butane to 1,4-dicarbazolylbutane

The quantum yields of stepwise cyclization of the first and second diphenylamino groups in 1,4-bis(diphenylamino)butane are 0.3 and 0.02, respectively, which indicates quenching of the excited diphenylamino group by a carbazole unit in the asymmetric semicyclized compound.