Observation of tunable two-photon induced excited-state and three-photon absorption phenomena by structure in oligomerfluorene derivatives

The nonlinear optical properties, including two-, three-photon and excited-state absorption phenomena, were observed in three oligomerfluorene derivatives (abbreviated as OF3, OF5 and OF7) by femtosecond (450 fs) laser pulses. Their two-, three-photon and, excited-state absorption properties were studied by open Z-scan and pump-probe measurements. Interestingly, when the numbers of fluorene units increased from 3 to 5, and to 7, the corresponding absorption phenomena changed from three-photon to two-photon induced excited-state phenomena, showed strong structure dependence in these derivatives. The results offer a method to design and synthesize organic molecules for multiphoton materials. It was noted that the three-photon cross-section value (delta (3)) of OF3 was up to 1.36x10(-76) cm(6) s(2). Correspondingly, the two-photon (delta (2)) and excited-state cross-section (delta (e) ) values of OF5 and OF7 also were obtained, and they were 1230 GM and 0.91x10(-18) cm(2) for OF5, and 1780 GM and 1.18x10(-18) cm(2) for OF7, respectively.