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Abstract: We compare the effects of fluorene–ethylene (FE) spacers on the photo-physical properties of fluorenone-based conjugated oligomers. The introduction of FE spacer could modulate the steady-state spectra and weaken the difference between donor-dependent spectral features. Meanwhile, the quantum chemical calculations exhibit that the electron transition mechanism modulated by FE unit is variable with the donor of oligomers. The FE π-spacer mainly rises the HOMO and facilitates the electron delocalization in the fluorene end-capped oligomer, while it lowers the LUMO and enhances the donor effect in the triphenylamine end-capped one. The time-resolved fluorescence measurement exhibits that the difference between donor-dependent excited state lifetimes of oligomers becomes less obvious after the introduction of FE units. Moreover, the nonlinear optical measurements show that the FE spacer is able to improve the two-photon fluorescence efficiency and enhance the two-photon absorption cross-section of oligomers simultaneously, but the difference in two-photon characteristics between oligomers with different donors is also decreased. [Copyright &y& Elsevier]

Abstract: We systemically investigate the photophysical properties of two star-shaped truxene based oligomers with different oligo(fluorene-vinylene) arms (Tr-OFV1 and Tr-OFV3) in solution system. The chemical quantum calculation exhibits that the electronic transition depends on the number of fluorene-vinylene (FV) groups in oligomers. The transient absorption (TA) data exhibits that increasing of FV groups in branch arms could accelerate the relaxation of excited oligomers, and the intensity-dependent exciton–exciton annihilation behavior could appear in the relaxation process of excited Tr-OFV3 and disappear in that of Tr-OFV1, indicating that their photophysical behavior is also closed to the number of FV unit. [Copyright &y& Elsevier]