Photophysical studies of mixed furan, pyrrole, and thiophene-containing oligomers with three and five rings

The photophysics of several oligomers containing mixed furan, pyrrole, and thiophene heterocyclic systems is reported. The mixed systems contain three rings and five rings of the heterocycles. Comprehensive spectroscopic and photophysical data were obtained and all of the rate constants kF, kIC, and kISC were evaluated. The lowest singlet excited state is of (1)B-like origin in any solvent. It is possible to have a reasonable understanding of the photophysics of the mixed ring systems compared to all the thiophene analogs if it is considered that some π–electron decoupling occurs at the site of the pyrrole or furan substitution, although this cannot be the total answer, as is discussed.