Linear and Nonlinear Optical Properties of Photoresponsive [60]Fullerene Hybrid Triads and Tetrads with Dual NIR Two-Photon Absorption Characteristics.

Two C-60-(antenna)(x) analogous compounds having branched hybrid triad C-60(>DPAF-C-18)(>CPAF-C-2M) and tetrad C-60(>DPAF-C-18) (>CPAF-C-2M)(2) nanostructures were synthesized and characterized. The structural design was intended to facilitate the ultrafast femtosecond intramolecular energy transfer from photoexcited C-60[>(1)(DPAF)*-C-18](>CPAF-C-2M)(1 or 2) or C-60(>DPAF-C-18)[>(1)(CPAF)*-C-2M](1 or 2) to the C-60> cage moiety upon two-photon pumping at either 780 or 980 nm, respectively. The latter nanostructure showed approximately equal extinction coefficients of optical absorption over 400-550 nm that corresponds to near-IR two-photon-based excitation wavelengths at 780-1100 nm for broadband nonlinear optical (NLO) applications. Aside from their enhanced two-photon absorption (2PA) activity at 780 nm, we also demonstrated ultrafast photoresponses at 980 nm showing 2PA cross-section (sigma(2)) values of 995-1100 GM for the hybrid tetrad. These sigma(2) values were correlated to the observed good efficiency in reducing femtosecond light-transmittance down to 3596 at the light intensity of 110 GW/cm(2). Accordingly, 2PA characteristics of these nanostructures at multiple NIR wavelengths provided support for their suitability in uses as broadband NLO nanomaterials at 600-1100 nm that includes the 2PA ability of two antenna, DPAF (700-850 nm) and CPAF (850-1100 nm), and the fullerene cage at shorter wavelengths (600-700 nm).