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(CH 2 ) 2 OSi i Pr 3 , 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 C 6 F 5 end-groups, [10PFV-3PV]F 2 , 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 (C 6 F 5 vs C 6 H 5 ). Timeresolved of fluorescence signals for [10PFV-3PV]F 2 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. ■ INTRODUCTIONConjugated polymers are of continuing interest as organic electronics due to their promising applications in optoelectronic and electrochemical devices, 1−5 such as photovoltaic cells, 3b light-emitting diodes, 5c,6 sensors, 5d,7 electrochromics, 8 and field-effect transistors. 5a,b,9 The synthesis of structurally regular, chemically pure polymers by development of new synthetic methods attracts notable attention 1 because their device performances are governed by the structural regularity, chemical purity, and supramolecular order. 2,3 Emerging applications of conjugated polymers require the patterning of materials on the nanometers length scale, and block copolymers made of covalently linked polymers represent an ideal route to control the self-assembly of the nanosized morphologies. Formation of regular one-dimensional conjugated structures on the nanoscale should be thus expected by exploiting the specific assembling properties of rod−coil block copolymers. 10−13 End-group modification of conjugated polymers has also been considered as an attractive topic of investigation because the important properties that have been demonstrated for end-functional conjugated polymers and the significant effect end-groups can have on electronic properties. For example, simple end-capping of conjugated polymers via postpolymerization reactions showed improvement in the performance of bulk heterojunction photovoltaic devices by eliminating traps for charge carriers. 14 Many reports concerning poly(fluorene)s (PFs) containing discrete end-groups (such as triarylamines, perylene mon...

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The singlet-singlet energy transfer rate in a new zinc(II) porphyrin-free base porphyrin dimer, having a m-bis(phenylethynyl)phenylene bridge, was found to be slower than that in the corresponding p-bis(phenylethynyl)phenylene-bridged dimer, despite the shorter donor-acceptor distance and pathway. The slower rate is interpreted as evidence for a major contribution of the superexchange mechanism.