The Institute for Lasers, Photonics and Biophotonics, State University of New York at Buffalo, Buffalo, New York 14260, USA.
J Am Chem Soc. 2011 May 4;133(17):6675-80. doi: 10.1021/ja1113112. Epub 2011 Apr 7.
Molecular chromophores with twisted π-electron systems have been shown to possess unprecedented values of the quadratic hyperpolarizability, β, with very large real parts and much smaller imaginary parts. We report here an experimental and theoretical study which shows that these twisted chromophores also possess very large values of the real part of the cubic hyperpolarizability, γ, which is responsible for nonlinear refraction. Thus, for the two-ring twisted chromophore TMC-2 at 775 nm, relatively close to one-photon resonance, n(2) extrapolated to neat substance is large and positive (1.87 × 10(-13) cm(2)/W), leading to self-focusing. Furthermore, the third-order response includes a remarkably low two-photon absorption coefficient, which means minimal nonlinear optical losses: the T factor, α(2)λ/n(2), is 0.308. These characteristics are attributed to closely spaced singlet biradical and zwitterionic states and offer promise for applications in all-optical switching.
具有扭曲π电子体系的分子生色团被证明具有前所未有的二次超极化率β值，其实部很大，虚部很小。我们在这里报告了一项实验和理论研究，表明这些扭曲生色团还具有非常大的三阶超极化率γ的实部，γ是非线性折射的原因。因此，对于在 775nm 处相对接近单光子共振的双环扭曲生色团 TMC-2，在纯净物质中 n(2)的外推值较大且为正（1.87×10(-13)cm(2)/W），导致自聚焦。此外，三阶响应包括一个显著低的双光子吸收系数，这意味着最小的非线性光学损耗：T 因子，α(2)λ/n(2)，为 0.308。这些特性归因于紧密间隔的单线态双自由基和两性离子态，并为全光开关应用提供了希望。
