ΔΛ-Isomerism of Mixed 1,3-Diketonate Complexes of Ru(III)A Designed New Source of Chirality in Nematic Liquid Crystals

Abstract

A high-power chiral dopant system involving 6-coordinate metal complexes was designed on the basis of a shape model. Accordingly, a series of mixed 1,3-diketonate complexes of Ru(III), [Ru(acac) 2 (L-n)], in which acac ) acetylacetonate and L-n ) dibenzoylmethanate substituted with n octyloxy groups (abbreviated as Ru-n hereafter), was prepared and optically resolved. Their performance as chiral dopants was evaluated in terms of helical twisting power (HTP) in a room-temperature nematic liquid crystal, N-(4-methoxybenzylidene)-4-n-butylaniline (MBBA), by measuring the helical pitch lengths and CD spectra for the induced chiral nematic phases. The ∆-and Λ-enantiomers induced macroscopic lefthanded (M) and right-handed (P) helices, respectively, and the (absolute) values for HTP have proven to be remarkably large, e.g. M ) 1.8 × 10 2 µm -1 in the case of Λ-Ru-2. The induced CD spectra for the dilute MBBA* materials (the asterisk denotes in this paper that MBBA has been doped with a chiral substance) were fit to the interpretation that persistent helical alignment of host molecules was generated. We also performed quantum chemical calculations for the optimum configuration of model Al(III) complexes with and without MBBA molecules and found that two liquid crystal molecules will eventually form a negative dihedral angle (left-handed twist) over the ∆-enantiomer of dialkylated complex.

Tris(β-diketonato) Ru(III) Complexes as Chiral Dopants for Nematic Liquid Crystals: the Effect of the Molecular Structure on the Helical Twisting Power

“…The result is different from the case of Ru-n, in which biaxial complexes showed lower HTPs than the uniaxial complex. 21 We now deduce the result of a theoretical calculation based on a surface chirality model to interpret the different HTPs among the Ru(III) complexes. 25 (1) where R is the gas constant, T is the temperature, K 22 is the twist elastic constant, ξ is the interaction energy, and υ m is the molar volume of the solution.…”

“…Ru(III) complexes (RuC 8 -1, RuC 8 -2, RuC 8 -3, RuC 0 -3, and RuC 24 -3) discussed in the present paper and two types of complexes (Ru-para and Ru-n) reported in a previous paper. 21 After stirring for a total of three days, the solvent was removed by evaporation, and the residue was subjected to silica gel column chromatography with benzene as an eluent. From the first eluted band, [Ru(acac) 2 (acacC 8 )] was isolated as a violet solid (0.306 g, 51% yield).…”

Simple and highly efficient chiral dopant molecules possessing both rod- and arch-like units

“…120-121 C (from chloroform-n-hexane); R f ¼ 0.77 (chloroform); n max (KBr, cm À1 ): 3037 (C-H), 2930 (C-H), 2860 (C-H), 1749 (C]O); d H (300 MHz, CDCl 3 ; Me 4 Si; ppm): 0.89 (6H, m, Me), 1.20-1.89 (32H, m, -CH 2 -), 2.38 (2H, s, CH), 3.52 (2H, s, CH), 3.99 (4H, t, J 1,2 ¼ 6.6 Hz, -OCH 2 -), 6.96 (4H, m, aromatic-CH), 7.14 (4H, m, aromatic-CH), 7 Example of measurement of HTP by the Cano method 5CB doped with 0.5 mol% of (R)-1 was put in a Cano wedge cell. The pitch length was measured by using a polarized optical microscope.…”

Chelated Boronate–Imine and Boronate–Amine Complexes as Chiral Dopants for Nematic Liquid Crystals

“…Metal complexes featuring a stereogenic metal center in addition to chiral ligands seem to open an entry to a large variety of chiral dopants due to the manifold combinations of different ligands and central atoms. This concept has been realized by using tris(dionato)metal complexes of chromium, cobalt, rhodium and ruthenium7a,7b as well as binaphthol‐derived titanium complexes 7c. The fact that bis(chelated) alkoxy(imine)titanium complexes developed by us7d–7f and, more recently, tetrapyrrol‐derived zinc complexes7g gave the so far highest HTP values (up to 740 μm –1 and 920 μm –1 , respectively) may illustrate the efficiency of metal‐containing dopants.…”