Structural Effects on the Low Cubic Hyperpolarizability of C_(60): A Scaling of Conjugation in Three-dimensional Curvature of #pi#-Conjugation Systems

摘要

The semiempirical AM1-calculated cubic hyperpolarizability is found to be surprisingly low in C_(60), which is in agreement with recent experimental results. (In the past, 10 orders of magnitude discrepancy has existed in the literature for the cubic hyperpolarizabilities of C_(60)). Comparing some selected groups of polyaromatic hydrocarbons, we show that linearity and planarity are tow dominating factors in the second hyperpolarizability in polyaromatic rings. Therefore, the observations that aromatic rings on C_(60) lose their linearity and planarity account for the low second hyperpolarizability. Furthermore, the planarity defined mathematically can be served as a scale of conjugation in #pi#-conjugation systems. By using biphenyl as a reference, the cubic hyperpolarizability of C_(60) can be estimated by the scaling of conjugation.