Synthesis, strong two-photon absorption, and optical limiting properties of novel C(70)/C(60) derivatives containing various carbazole units.

An approach was demonstrated toward the design and synthesis of a series of novel C(70) and C(60) derivatives for large two-photon absorption (TPA). The molecular structures of fullerene derivatives were confirmed by MALDI-MS, (1)H NMR, and FT-IR. With femtosecond open-aperture Z-scans and frequency-degenerate pump-probe measurements at 780 nm, the TPA cross sections of up to 3.47 x 10(-46), 1.64 x 10(-46), 1.1 x 10(-46), and 7.82 x 10(-47) cm(4) s photon(-1) molecule(-1) were determined for C(70)-TCTA, C(60)-TCTA, C(70)-BCzMB, and C(70)-MQEtCz in toluene with concentrations of 10(-4) M, respectively. The normalized light transmittances of solutions of these molecules were attenuated to the range between 33% and 50% for C(70)-TCTA, C(60)-TCTA, C(60)-BCzMB, and C(70)-MQEtCz as the input irradiance was increased to about 150 GW/cm(2), showing that they are effective optical limiters. Both intensity-dependent Z-scans and pump-probe experiments confirmed that the reduction in the light transmittance results mainly from the TPA process. In addition, the molecule concentration dependence of the TPA cross sections was also investigated. It was found that the TPA cross sections are extremely sensitive to the concentration with the greatest TPA cross-section of 1.0 x 10(-45) cm(4) s photon(-1) molecule(-1) for C(70)-TCTA measured in the low concentration regime ( approximately 10(-5) M).