Intermolecular interaction effects on second hyperpolarizabilities of clusters including charged species

Article type: Research Article

Authors: Nakano, Masayoshi^{; *} | Kishi, Ryohei | Nakagawa, Nozomi | Ohta, Suguru | Takahashi, Hideaki | Furukawa, Shin-ichi

Affiliations: Division of Chemical Engineering, Department of Materials Engineering Science, Graduate School of Engineering Science, Osaka University, Toyonaka, Osaka 560-8531, Japan

Correspondence: [*] Corresponding author. E-mail: mnaka@cheng.es.osaka-u.ac.jp.

Abstract: We investigate the intermolecular-interaction effects on the longitudinal second hyperpolarizabilities (γ) for two types of π-π stacking clusters: C5H7+ dimer and π-conjugated main chains (CnHn+2, 6⩽n⩽16) interacting in both end regions with two allyl cations (C3H5+). The γ values are calculated by the finite-field approach using several ab initio molecular orbital and density functional methods. It is found that in the first model the π-π interaction between the upper and lower π-orbitals significantly reduces the magnitude of effective γ per monomer, while the second model exhibits a remarkable enhancement of γ values as compared to those of isolated main chains. The analysis using the hyperpolarizability density and orbital interaction elucidates that the reduction of longitudinal γ value in the first model originates in the reduction of longitudinal π-conjugated electron distributions due to the perpendicular π-π orbital interactions, whereas the enhancement of longitudinal γ in the second model is caused by the intermolecular charge transfer between both end perturbing molecules via the main chain. On the basis of these results, we discuss a novel guideline of controlling third-order nonlinear optical properties of clusters.

DOI: 10.3233/JCM-2006-61-417

Journal: Journal of Computational Methods in Sciences and Engineering, vol. 6, no. 1-4, pp. 211-222, 2006