We report a newly synthesized polymer of a star-shaped porphyrin compound(TPA-FxP) with four oligofluorene arms at its meso positions with the pronounced enhancement of the two-photon properties and the generation of singlet oxygen by utilizing the two-photon excited fluorescence resonance energy transfer.The steady-state spectra and transient triplet-triplet absorption spectra give evidence that the enhanced two-photon absorption cross section results from not only the through-space energy transfer(Frster) but also the through-bond energy transfer between conjugated peripheral oligofluorene arms and the porphyrin core.The two-photon absorption cross section at 780 nm up to 3360 GM(1 GM = 10-50 cm4·s/photon) of TPA-FxP was obtained,which is comparable to the highest values reported from other similar chemically modified porphyrin core compounds.Furthermore,the enhanced production of singlet oxygen under two-photon absorption conditions is also reported.
The rapid internal conversion dynamics at room temperature is determined by using the femtosecond time-resolved fluorescence depletion measurements of a complex solvated molecule of LD 700 （rhodamine 700） combined with steadystate absorption and fluorescence spectroscopy, as well as quantum chemical calculation. The molecule is excited by a 50 fs laser pulse at 400 nm which directly populated the highly excited singlet state, the rapid internal conversions （ICs） are observed, which leads to the directional changes of the emission transition moment following photoexcitation to the highly excited singlet state S5 of LD 700.
