Time-Resolved Fluorescence Spectra in the End-Functionalized Conjugated Triblock Copolymers Consisting of Poly(fluorene vinylene) and Oligo(phenylene vinylene): Proposal of Dynamical Distortion in the Excited State

Time-resolved fluorescence study has been explored for end-functionalized conjugated triblock copolymers consisting of poly­(9,9-di-n-octylfluorene-2,7-vinylene)­s (PFVs, FV repeat units ca. 10 or 20) and oligo­(2,5-dialkoxy-1,4-phenylene­vinylene)­s [OPV, alkoxy = O­(CH₂)₂OSiⁱPr₃, 3 or 7 PV repeat unit] as the middle segment. Unit (FV and PV) length dependence of each block on fluorescence was examined. The polymer sample having three PV repeat units as the middle segment with C₆F₅ end-groups, [10PFV-3PV]­F₂, showed time-dependent fluorescence spectra, in which relative intensities of the vibronic bands increase in later delay time, whereas similar observations were not seen in the other polymer samples containing 7PV as the middle segment even by varying the PFV chain lengths (ca. 20) or the end-group (C₆F₅ vs C₆H₅). Time-resolved of fluorescence signals for [10PFV-3PV]­F₂ can be analyzed by assuming two components: one is a faster decay component and the other is a slower red component, which rises with the time constant of the former one. On the other hand, the other three polymer samples showed single-exponential decays without significant wavelength dependence. Dynamical structural relaxation in the excited state is proposed as the origin of time dependence of the fluorescence spectra in the polymer having 3PV repeat unit on the basis of analysis of time-resolved fluorescence signals as well as viscosity dependence.