Optical limiting properties and ultrafast response of three oligomers based on 1,3,5-triazine

Three tri-branched oligomers based on 1,3,5-triazine with large two-photon absorption cross-sections and good optical limiting properties were investigated by UV-Visible, femtosecond Z-scan and one/two-color pump-probe measurements. The two-photon absorption cross-section results measured at a wavelength of 800 nm were found decreasing with the number of fluorene groups in each branches. The optical limiting properties were also investigated and a two-photon absorption mechanism was proposed. One/two-color pump-probe measurements were also used to further investigate the ultrafast responses of these tri-branched oligomers. The ultrafast response results indicated that after excitation, the tri-branched oligomers will first undergo a fast process to form an intramolecular charge transfer state followed by relaxation of the intramolecular charger transfer state of approximately several hundred ps.