Three-photon absorption of a new series of halogenated fluorene derivatives

In this Letter, we report the characterization of the pure three-photon absorption and the measurement of the three-photon absorption cross-section (σ₃^′) of a new series of halogenated fluorene derivatives. The three-photon absorption of these compounds corresponds to the S₀ → S₁ electronic transition. All four compounds presented here have potential application as photosensitizers in deep photodynamic therapy induced via high order nonlinear absorption. The measurements were done using a tunable OPG pumped by a 25 ps Nd-YAG laser, and performing transmittance vs. input intensity as well as open aperture Z-scan at different wavelengths to determine the highest value of σ₃^′.