The photo-physical properties of oligo（fluorene-vinylene） functionalized anthracene linear oligomers （An-OFVn （n=1-4）） have been systemically investigated through experimental and theoretical methods. The steady-state spectral measurement shows that the increasing of fluorene-vinylene （FV） group could lead to the red shift of absorption spectra and restrain the excimer formation between oligomers. Quantum chemical calculations exhibit that the energy levels of HOMO, LUMO, and the band gap gradually converge to a constant in accompany with the increasing of FV unit. Meanwhile, the electronic cloud which distributes on the branch arms, also gradually enhances and makes the absorption spectral shape of oligomers become similar to that of branch arms step by step. The time-resolved fluorescence tests exhibits that the lifetime of excimer emission would be almost invariable after the number of FV group in oligomer is ≥2. In nonlinear optical test, the two-photon photoluminescence efficiency and two-photon absorption cross-section will both gradually enhance and be close to an extremum after the number of FV unit is equal to 4. These results will provide a guideline for the design of novel photo-electronic materials.
The excited state photophysics of low bandgap polymer APFO3 has been investigated in detail. The chemical calculations confirm that the intrachain charge transfer （ICT） may occur after photo-excitation and is mainly responsible for the first absorption band. The transient absorption results confirm that ICT indeed exists and competes with the vibra-tional relaxation at the same time, when APFO3 is in a monodisperse system. This ICT process would disappear due to the influence of interchain interaction when APFO3 is in the condensed phase, where the exciton decay would be dominant in the relaxation process after photoexcitation. The photoexcitation dynamics of APFO3 film blending with PC61BM are presented, which shows that the exciton may be dissociated completely as the percentage of PC61BM reaches ～50%. Meanwhile, the photovoltaic performance based on blend het-erojunction shows that the increase of photocurrent is little if the percentage of PC61BM exceeds ～50%. Overall, the present study has covered several fundamental processes taking place in the APFO3 polymer.
The photo-physical characteristics of semiconductor polymer are systematically stud- ied through comparing poly （9,9-dioctylfluorene） （PFO） and poly （9,9-dioctylfluorene-co- benzothiadiazole） （F8BT）. The quantum chemical calculation shows that the introduction of benzothiadiazole unit facilitates the intrachain charge transfer （ICT） and modulates the electronic transition mechanism of polymer. The transient absorption measurement exhibits that intrachain exciton relaxation is dominant in the decay of excited PFO in a monodis- perse system and intrachain exciton interaction could appear at high excitation intensity. In F8BT solution, the ICT state exists and participates in the relaxation of excited state. The relaxation processes of PFO and F8BT in the condensed phase both accelerate and show obvious exciton-exciton annihilation behavior at high excitation intensity. At the same excitation intensity, the mean lifetime of F8BT is longer than that of PFO, which may be assigned to the excellent delocalization of charge.
