Synthesis and fluorescence properties of unsymmetrical 1,4-dihydropyrrolo[3,2-b]pyrrole dyes

Despite being regioisomers, unsymmetrical 1,4-dihydropyrrolo[3,2- b ]pyrroles 5 and 6 showed significantly different absorption and fluorescence properties due to the difference of the resonance structure between 5 and 6.