Optical Properties of Oligo(fluorene-vinylene) Functionalized Anthracene Linear Oligomers: Effect of π-extension

The photo-physical properties of oligo(fluorene-vinylene) functionalized anthracene linear oligomers (An-OFV_n (n=1-4)) have been systemically investigated through experimental and theoretical methods. The steady-state spectral measurement shows that the increas-ing 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 con-stant 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.