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The effects of π-spacer and electron donor groups on the photophysical behaviors of fluorenone-based linear conjugated oligomers have been systemically investigated. Solvent-dependent steady-state measurements exhibit that the fluorene vinylene ( FV) spacer and the electron-donating ability of donor group are able to modulate the spectral features of oligomers and the fluorescence quantum yield could decrease with the increasing of the solvent polarity. Meanwhile, quantum chemical calculation simulates their absorption spectra, and analyzes their electron transition components simultaneously. The transient absorption measurements focus on the photoexcitation dynamics of these oligomers in the toluene solution, which show that an intramolecular charge transfer state exists in the relaxation process of excited states, and its generation process could accelerate with the introduction of FV spacer and the enhancement of donor strength. [ABSTRACT FROM AUTHOR]

Highlights: [•] Two fluorine (F) based oligomers are synthesized and investigated in detail. [•] F units modulate the steady-state spectra of oligomers. [•] DFT calculations analyze molecular structure and the electronic transition. [•] F units increase the TPF efficiency and the TPA cross-section of oligomers. [•] F units shorten the lifetime of excited oligomers. [Copyright &y& Elsevier]

Highlights: [•] The simulated absorption spectra of oligomers are achieved. [•] The lowest energy band of experimental absorption spectra is assigned. [•] TA measurements give the relaxation process of polymer in CB solution and solid film. [ABSTRACT FROM AUTHOR]

Highlights: [•] π-Spacer dependent optical properties of fluorenone-based oligomers are studied. [•] Fluorene–ethylene (FE) spacer could modulate the steady-state spectra of oligomers. [•] DFT calculations confirm the ICT nature in the HOMO–LUMO transition. [•] FE spacer could increase the TPPL efficiency and TPA cross-section of oligomers. [•] TA measurement confirms the ICT state exists in the relaxation of excited oligomer. [Copyright &y& Elsevier]

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]

Abstract: Experimental and theoretical studies on the donor-dependent optical characteristics of two D–π–A–π–D type linear fluorenone-based conjugated oligomers are presented, where fluorene and triphenylamine act as the donors, respectively. Because of the strong electron-donating ability, the triphenylamine chromophores lead to red-shifts of spectral features, shorten the excited state lifetime, and enhance the two-photon fluorescence efficiency and two-photon absorption cross-section in comparison with fluorene groups. Quantum chemical calculations provide complementary information regarding the molecular structures and the frontier orbitals, which can provide a deep insight into the electronic structure and properties of oligomers. [Copyright &y& Elsevier]