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

Two C₆₀-(antenna)_x analogous compounds having branched hybrid triad C₆₀(>DPAF-C₁₈)(>CPAF-C_2M) and tetrad C₆₀(>DPAF-C₁₈)(>CPAF-C_2M)₂ nanostructures were synthesized and characterized. The structural design was intended to facilitate the ultrafast fs intramolecular energy-transfer from photoexcited C₆₀[>¹(DPAF)*-C₁₈](>CPAF-C_2M)_1or2 or C₆₀(>DPAF-C₁₈)[>¹(CPAF)*-C_2M]_1or2 to the C₆₀> 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 photo-responses at 980 nm showing 2PA cross-section (<i>σ</i>₂) values of 995-1100 GM for the hybrid tetrad. These <i>σ</i>₂ values were correlated to the observed good efficiency in reducing fs light-transmittance down to 35% at the light intensity of 110 GW/cm². 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).