Crystal Structures, Degree of Charge Transfer, and Non-Linear Optical Characteristics of Intramolecular Charge-Transfer Compounds: Indoline-Substituted Tricyanoquinodimethanes
作者:Tsuyoshi Murata、Gunzi Saito、Kazukuni Nishimura、Chin-Hong Chong、Masaru Makihara、Genki Honda、Yuichiro Enomoto、Salavat Khasanov、Hideki Yamochi、Akihiro Otsuka、Kenji Kamada、Koji Ohta、Jun Kawamata
DOI:10.1246/bcsj.81.1131
日期:2008.9.15
The substituent effect on the degree of intramolecular charge transfer (δ) and optical properties of donor–π–acceptor compounds comprised of 1,3,3-trimethyl-2-methyleneindoline (I1) and substituted 7,8,8-tricyanoquinodimethane (=2-(4-cyanomethylene-2,5-cyclohexadienylidene)malononitrile, 3CNQ-R, R = substituent groups) moieties were investigated (I1–3CNQ-R). In the crystal structures, I1–3CNQ-R molecules stacked on indoline and/or 3CNQ-R moieties in a head-to-tail manner to cancel their dipole moments and established segregated or mixed stack columnar motifs. The δ values of I1–3CNQ-R molecules in solid and solution states were estimated using the bond length ratio in the crystal structures, molecular orbital calculation, and the solvatochromic shift of intramolecular charge-transfer absorption, respectively, and showed significant and reasonable dependences on substituents of the 3CNQ moiety. Structural analysis revealed that molecular conformation and planarity affect the δ values of I1–3CNQ-R molecules. Molecular orbital calculations revealed that molecular (hyper)polarizabilities can be modulated by tuning δ. I1–3CNQ-R exhibited a solvatochromic shift, and the ground state changed from neutral (δ≤0.5) in less-polar solvents to ionic (δ≥0.5) in polar solvents. Two-photon absorption properties of I1–3CNQ-R showed a significant substituent effect and indicated that δ is a fundamental parameter for modulating non-linear optical properties.
取代基对由1,3,3-三甲基-2-亚甲基吲哚啉(I1)和取代的7,8,8-三氰基喹诺二甲烷(=2-(4-氰基亚甲基-2,5-环己二烯亚基)丙二腈,3CNQ-R,R=取代基基团)组成的供体-π-受体化合物的分子内电荷转移程度(δ)和光学性质的影响(I1-3CNQ-R)。在晶体结构中,I1-3CNQ-R分子以头对尾的方式堆积在吲哚啉和/或3CNQ-R基团上以消除其偶极矩,并建立了分离或混合的堆叠柱型图案。使用晶体结构中的键长比、分子轨道计算和分子内电荷转移吸收的溶剂化色移分别估计了I1-3CNQ-R分子在固体和溶液状态下的δ值,并显示出对3CNQ基团的取代基的显著和合理的依赖关系。结构分析表明,分子构象和平面性影响I1-3CNQ-R分子的δ值。分子轨道计算表明,通过调节δ可以调节分子的(超)极化率。I1-3CNQ-R表现出溶剂化色移,基态从较低极性溶剂中的中性态(δ≤0.5)变为极性溶剂中的离子态(δ≥0.5)。I1-3CNQ-R的双光子吸收性质显示出显著的取代基效应,表明δ是调节非线性光学性质的基本参数。