Synthesis and photoinduced electron-transfer process of a novel triphenylamine-substituted polyfluorene-C₆₀ triad

The photoinduced electron-transfer process of a newly prepared, soluble, π-conjugated poly[9,9-bis(4-diphenylaminophenyl)-2,7-fluorene] (PDPAF), covalently bridged, C₆₀ triad (C₆₀-PDPAF-C₆₀) is described. The molecular orbital calculations revealed that the majority of the highest occupied molecular orbital (HOMO) is located on the polyfluorene entity, while the lowest unoccupied molecular orbitals (LUMO) are found to be entirely n the C₆₀ entity. The excited-state electron-transfer processes were monitored by both steady-state and time-resolved emission as well as by transient absorption techniques in toluene and benzonitrile. By excitation of the polyfluorene moiety, fluorescence quench- ng of the singlet excited state of poly-fluorene moiety was observed. The nanosecond transient spectra in near-IR region revealed the charge-separation process from the polyfluorene moieties to the C₆₀ moiety through the excited singlet states of polyfluorene. The lifetimes of the charge separated states were evaluated to be 20-50 ns, depending on the solvent polarity.