Department of Chemistry and ‡Department of Physics, School of Science, Kitasato University , 1-15-1 Kitasato, Minami-ku, Sagamihara, Kanagawa 252-0373, Japan.
Inorg Chem. 2013 Oct 7;52(19):11042-50. doi: 10.1021/ic401240f. Epub 2013 Sep 13.
Doping nematic liquid crystals with optically active compounds transforms them into chiral nematic phases with helical structures. In this phenomenon, the chirality of the dopant molecules is transferred or amplified to the bulk of the liquid crystals. Δ-[Ru(acac)3] (acac = acetylacetonato) is known to work as one of the dopants with a strong helical twisting power (HTP). In this study, we have systematically modified [Ru(acac)3] to clarify the correlation between the molecular structure and HTP; we have designed and synthesized five new Ru(III) complexes, [Ru(acac)2(acacC8)] (RuC8-1, acac = acetylacetonate, acacC8 = 3-(4'-octyloxy-phenylalkynyl)-pentane-2,4-dionato), [Ru(acac)(acacC8)2] (RuC8-2), [Ru(acacC8)3] (RuC8-3), [Ru(acacC0)3] (RuC0-3, acacC0 = 3-(phenylalkynyl)-pentane-2,4-dionato), and [Ru(acacC24)3] (RuC24-3, acacC24 = 3-(3',4',5'-tri(octyloxy)-phenylalkynyl)-pentane-2,4-dionato). All the complexes, except for RuC0-3, could be separated into Δ, Λ isomers by HPLC on a chiral column and were examined as chiral dopants for a nematic liquid crystal, N-(4-methoxybenzilidene)-4-butylaniline (MBBA). The Δ isomers of RuC8-1, RuC8-2, RuC8-3, and RuC24-3 induced a right-handed (P) helix and the magnitudes of the HTPs (/μm(-1)) were determined as follows: RuC8-1 (+60) < RuC8-2 (+109) > RuC8-3 (+78) > RuC24-3 (+41). The HTPs of the ruthenium dopants were not simply proportional to their size. The highest HTP observed in biaxial RuC8-2 was attributed to the balance of the molecular helicity and high ordering in MBBA based on the surface chirality model.
向各向异性向列液晶中掺杂光学活性化合物，可将其转变为具有螺旋结构的手性向列相。在这种现象中，掺杂剂分子的手性被传递或放大到液晶的主体中。已知 Δ-[Ru(acac)3]（acac = 乙酰丙酮酸盐）是一种具有强螺旋扭转力（HTP）的掺杂剂之一。在这项研究中，我们系统地对 [Ru(acac)3] 进行了修饰，以阐明分子结构与 HTP 之间的相关性；我们设计并合成了五个新的 Ru(III) 配合物，[Ru(acac)2(acacC8)]（RuC8-1，acac = 乙酰丙酮酸盐，acacC8 = 3-(4'-辛氧基-苯乙炔基)-戊烷-2,4-二酮），[Ru(acac)(acacC8)2]（RuC8-2），[Ru(acacC8)3]（RuC8-3），[Ru(acacC0)3]（RuC0-3，acacC0 = 3-(苯乙炔基)-戊烷-2,4-二酮）和[Ru(acacC24)3]（RuC24-3，acacC24 = 3-(3',4',5'-三(辛氧基)-苯乙炔基)-戊烷-2,4-二酮）。除了 RuC0-3 之外，所有的配合物都可以通过手性柱上的 HPLC 分离为 Δ、Λ 异构体，并被用作向列液晶 N-(4-甲氧基苯亚甲基)-4-丁基苯胺（MBBA）的手性掺杂剂进行了测试。RuC8-1、RuC8-2、RuC8-3 和 RuC24-3 的 Δ 异构体诱导出右手（P）螺旋，HTP 的大小（/μm(-1))如下：RuC8-1 (+60) < RuC8-2 (+109) > RuC8-3 (+78) > RuC24-3 (+41)。钌掺杂剂的 HTP 与其尺寸不成正比。在双轴 RuC8-2 中观察到的最高 HTP 归因于基于表面手性模型的分子螺旋性和 MBBA 中高有序性之间的平衡。
