Effects of terthiophene as the end-groups in triblock copolymers consisting of poly(fluorene vinylene) and oligo(phenylene vinylene): Time-resolved fluorescence and its anisotropy

Abstract

Effects of terthiophene (3T) as the end-groups in poly(9,9-di-n-octyl-fluorene-2,7-vinylene)s (PFVs) were studied by means of time-resolved fluorescence and anisotropy techniques. In a terthiophene end-modified triblock copolymer consisting PFV and oligo(phenylene vinylene) (PV, as the middle segment), [(10PFV)2-7PV](3T)2, steady-state fluorescence spectrum shows much intense vibronic bands compared to those of the reference copolymer without terthiophene groups. In contrast, the absorption spectrum of [(10PFV)2-7PV](3T)2 was almost identical to that of the reference copolymer. Fluorescence quantum yield of the 3T end-modified polymer is significantly lower than that of the reference copolymer: ϕf = 0.62 vs 0.83. It was found that fluorescence spectral profile of [(10PFV)2-7PV](3T)2 is time-dependent: As the delay time increases, relative intensities of the higher vibronic bands increase. Time-resolved signals were analyzed by two decay components, 430 ps (shorter wavelength region) and 630 ps (longer wavelength region). On the other hand, fluorescence anisotropy ratios decrease as the monitored wavelength becomes longer. It is highly likely that the terthiophene end-modified copolymer undergoes structural change in the excited state. The longer decay component can be ascribed to a species of which π-system of the excited PFV part is expanded over the end-group after coplanarization of the terthiophene unit upon the excitation.