Photophysics of aminophenyl substituted pyrrolopyrrole cyanines.

A series of novel pyrrolopyrrole cyanines (PPCys) bearing various aminophenyl substituents at the diketopyrrolopyrrole (DPP) core are presented. Compared to their alkoxyphenyl substituted analogues, these dyes feature additional intense electronic transitions of charge-transfer character which give detailed insight into the optical properties of PPCys. The energetic mixing of the involved orbitals has pronounced effects on the absorption and fluorescence behavior. Protonation of the amino function suppresses these effects and leads to a pronounced increase in fluorescence quantum yield. The photophysics of the dyes can be rationalized by means of a simple energy scheme.