Two-dimensional charge-transfer molecular design for control of optical anisotropy

Abstract

A possibility to control anisotropy of refractive index due to poling through molecular geometry is investigated. As model compounds, 3,6-di(dicyanovinyl)-N-ethylcarbazole with two dimensional Charge Transfer (CT) character and its one dimensional CT counterpart, 3-dicyanovinyl-N-ethylcarbazole, were analyzed. In the molecular orbital calculations, the molecular geometries were optimized at the Austin model 1 level. To obtain photoexcited states, the INDO-SCI (Intermediate Neglect of Differential Overlap-Single Configuration Interaction) technique was applied. The components of the molecular polarizability tensors were obtained by means of the sum over states method. The tensors were transformed into a Cartesian coordinates system in which the molecular ground state dipole moment vector is z axis, and they were averaged over rotation around z axis. Finally, macroscopic molecular polarizability tensors were obtained by transforming into a Cartesian coordinates system in which the poling electric field is z axis. The macroscopic refractive indices are obtained from these macroscopic molecular polarizability tensors. It was shown that depending on the angle between the CT axes, opposite sign of anisotropy can be realized. In addition, a possibility to achieve high tolerance to molecular orientation relaxation using these two dimensional CT molecules was presented.

分子配置の分極処理に基づく屈折率異方性の制御可能性を研究した。モデル化合物として、2次元電荷移動型には3,6-ジ(ジシアノビニル)-N-エチルカルバゾールを、1次元型には3-ジシアノビニル-N-エチルカルバゾールを比較解析した。分子軌道計算において、分子配置はAustinモデル1準位で最適化した。光励起状態を得るために、INDO-SCI(Intermediate Neglect of Differential Overlap-Single Configuration Interaction)手法を適用した。分子分極率テンソルの成分は状態和の方法で求めた。テンソルは、分子基底状態の双極子能率ベクトルがz軸である直交座標系に変換し、z軸のまわりの回転で平均した。最後に、分極処理電場がz軸である直交座標系への変換で巨視的分子分極率テンソルを求めた。巨視的な屈折率は巨視的な分子分極率テンソルから求めた。電荷移動軸の成す角度に依存して、異方性の反対符号が実現できた。さらに、これらの2次元電荷移動型分子を使って、分子配向緩和を高精度に達成できることも示した。