Two-Photon Absorption Properties of Soluble Fluorene-based Conjugated Polymers

摘要

Soluble fluorene-based conjugated polymers are known for high chemical purity, high photoluminescence quantum yield, and small inhomogeneous broadening in the optical spectra. We have used two-photon absorption at room temperature of laser pulses at 804 nm of 200 fs duration with a repetition rate of 249 kHz to characterize two typical representatives of fluorene-based conjugated polymers. Poly(9,9-bis(2-ethylhexyl)fluorene-2,7-diyl) (PF), a material with an exceptionally high high photoluminescence quantum yield, is known for very defined optical spectra in emission and absorption. We detected strong blue emission as a result of two-photon absorption, which is remarkable for the polyfluorene since the onset of the optical absorption is at 400 nm. The material shows a strongly nonlinear behavior of the transmitted light intensity when plotted versus the pulse energy, and a clear quadratic intensity dependence of the PL emission on the same parameter.