Synthesis, Characterization, and Photoisomerization Studies of Azo- and Stilbene-Containing Surfactant Rhenium(I) Complexes

Several ruthenium(II) surfactants of general formula [Ru(bpy)(2)L](2+) [L = N-(2-pyridylmethylene)-3,4-bis(tetradecyloxy)benzenamine, N-(2-pyridylmethylene)-3,4-bis(octadecyloxy)benzenamine, 9-(3,4-bis(tetradecyloxy)benzenamino)-4,5-diazafluorene, 9-(4-(tetradecyloxy)-4'-azabenzenamino)-4,5-diazafluorene, 4,7-dinonadecyl-1,10-phenanthroline] and [Ru(L)(3)](2+) (L = 4,7-dinonadecyl-1,10-phenanthroline) were synthesized and characterized by elemental analysis, (1)H NMR, UV-vis, luminescence spectroscopy, and cyclic voltammetry. Their Langmuir-Blodgett (LB) film formation properties and surface pressure-area (pi-A) isotherms were also studied. Two complexes were found to show second-harmonic-generation (SHG) behavior.

Synthesis, characterization, Langmuir-Blodgett film-forming properties, and second-harmonic-generation studies of ruthenium(II) complexes with long hydrocarbon chains.

A large series of complexes has been synthesized with two chelating, Schiff base azobenzene derivatives connected linearly by coordination to a central nickel(II) or palladium(II) ion. These compounds have the general formulas M(II)(OC(6)H(3)-2-CHNR-4-N═NC(6)H(4)-4-CO(2)Et)(2) [M = Ni; R = n-Bu (3c), n-C(6)H(13) (3d), n-C(8)H(17) (3e), n-C(12)H(25) (3f), Ph (3g), OH (3h), C(6)H(4)-4-CO(2)Et (3i). M = Pd; R = i-Pr (4a), t-Bu (4b), n-Bu (4c), n-C(6)H(13) (4d), n-C(8)H(17) (4e), n-C(12)H(25) (4f), Ph (4g)], M(II)[OC(6)H(3)-2-CHN(n-C(8)H(17))-4-N═NC(6)H(4)-4-CO(2)(n-C(8)H(17))](2) [M = Ni (9), Pd (10)], M(II)[OC(6)H(3)-2-CHN(n-C(8)H(17))-4-N═NC(6)H(4)-4-C(6)H(4)-4-O(n-C(7)H(15))](2) [M = Ni (14), Pd (15)], and M(II)[OC(6)H(3)-2-CHN(CMe(2))-4-N═NC(6)H(4)-4-CO(2)Et](2) [M = Ni (17), Pd (18); the CMe(2) groups are connected]. These compounds have been characterized by using various physical techniques including (1)H NMR spectroscopy and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry. Single-crystal X-ray structures have been obtained for two pro-ligands and five complexes (3e, 4e, 14, 15, and 17). The latter always show a strictly square planar arrangement about the metal center, except for the Ni(II) complex of a salen-like ligand (17). In solution, broadened (1)H NMR signals indicate distortions from square planar geometry for the bis-chelate Ni(II) complexes. Electronic absorption spectroscopy and ZINDO_S (Zerner's intermediate neglect of differential overlap) and TD-DFT (time-dependent density functional theory) calculations show that the lowest energy transition has metal-to-ligand charge-transfer character. The λ(max) of this band lies in the range of 409-434 nm in dichloromethane, and replacing Ni(II) with Pd(II) causes small blue-shifts. Dichroic ratios measured in various liquid crystal hosts show complexation-induced increases with Ni(II), but using Pd(II) has a detrimental effect.

Nickel(II) and palladium(II) complexes of azobenzene-containing ligands as dichroic dyes

The optical properties of dyes dissolved in liquid crystals have led to their proposed use in a diverse range of practical applications. Such guest–host systems are typically required to fulfil a range of criteria relating to their absorption properties, degree of alignment and stability, but concurrently satisfying these requirements has proven a barrier to their widespread use. In this article, many of the proposed applications and their requirements are discussed, and an outline of some of the most prevalent classes of dye proposed in the context of guest–host systems is given, along with a summary of recent reports of dyes that exhibit thermotropic mesophases. Theoretical approaches to describing the alignment within guest–host systems are outlined, and possible strategies for the future rational design of guest–host systems are discussed.

https://www.tandfonline.com/doi/pdf/10.1080/02678292.2016.1189613

Dyes as guests in ordered systems: current understanding and future directions

Tris-, tetrakis-, and pentakisazo dyes have been prepared by the oxidation of 4-(arylazo)arylamines. Iodobenzene diacetate was the preferred oxidant for preparation of 4,4′-bis(arylazo)azobenzenes and 4,4′-bis(arylazo)-2,2′,3,3′,5,5′,6,6′-octafluoroazobenzenes, whereas silver(II) oxide proved a satisfactory oxidant for synthesis of 4,4′-(arylazo)(methyl-substituted)azobenzenes. Unsymmetrical tris- and tetrakisazo dyes were also obtained by cross oxidation. The absorption bands of these azo dyes were observed in the range of 381–472 nm in liquid crystals. The solubility of the trisazo dyes in hexane was the highest, followed by the tetrakis- and pentakisazo dyes. The unsymmetrical derivative having methyl groups in the central p-phenylene moieties was most soluble among the trisazo dyes. The order parameters (S) of the tris-, tetrakis-, and pentakisazo derivatives were in the range 0.66–0.81, sufficiently high for the practical application of these dyes in liquid crystal displays.

Synthesis of tris-, tetrakis-, and pentakisazo dyes and their application to guest–host liquid crystal displays

Novel disazo dyes containing tetrafluoro-p-phenylene moiety(ies) have been synthesized. The absorption bands of these compounds were observed in the range of 432−555 nm in ZLI-4792. The introduction of tetrafluoro-p-phenylene moieties in both the terminal ends was very effective in increasing the solubility. The 4-butylthio derivative was most soluble among the 4-(butylthio)-, 4-(alkoxy)-, and 4-(butylamino)tetrafluoro-p-phenylene derivatives. The dichroisms of all the tetrafluoro-p-phenylene derivatives were similar (S = 0.69−0.77) to those of the p-phenylene derivatives (0.68−0.76). These results indicate that the novel fluorine-containing disazo dyes can be practically used as dichroic dyes in guest−host liquid crystal displays.

Synthesis and Properties of Novel Dichroic Disazo Dyes Containing the Tetrafluoro-p-phenylene Moiety for Guest−Host Liquid Crystal Displays

In this paper, the authors conducted psychophysical tests to investigate the effect of the directionality of human tactile sensation capability in discriminating fine step-heights. We evaluated the capability of human finger to discriminate the step-heights of 0 to 20 µm moving at the angle of 0°, 45° and 90°. The results suggest that the different directions of touching motion affect the human tactile sensation for recognizing step-heights.

Directionality of human tactile sensation capability in discriminating fine step-heights

The purpose of this study is to investigate the directionality of the tactile sensation capability of human fingertip in recognizing fine step-heights of about 10 μm and discuss the mechanism of the directionality. We have developed a measurement system that presents a step-height to a subject fingertip and measures the human tactile sensation capability. The presentation device can control four parameters of the presentation, which are the step-height, the presentation velocity, the presentation angle, and the presentation temperature. In this paper, to investigate the finger’s tactile sense directionality, we conducted two kinds of psychophysical tests. In the tests, the step-heights of about 10 μm with three different presentation angles of 0, 45 and 90 degrees are used as the presentation stimuli. In the first psychophysical test, human subjects touch and distinguish, using the center of their fingertips, each pair of the step-heights that have the same presentation angles, 0 vs. 0, 45 vs. 45 and 90 vs. 90 degrees. In the other test, they distinguish each pair of the step-heights that have the different presentation angles, 0 vs. 0, 0 vs. 45 and 0 vs. 90 degrees. From these psychophysical tests, the difference thresholds and subjective equalities for the step-heights are determined and the relationship between the fine-step’s presentation angle and the fingertip’s tactile sensation is revealed. As a result, it is found that the step’s presentation angle has an influence on the human tactile sensation capability. In addition, the mechanism of the fingertip’s tactile sense directionality is discussed.

Naoki Tanaka

Papers

Synthesis and Properties of Novel Dichroic Disazo Dyes Containing the Tetrafluoro-p-phenylene Moiety for Guest−Host Liquid Crystal Displays

Directionality of human tactile sensation capability in discriminating fine step-heights

Directionality of Human Tactile Sense of Fingertip in Discriminating Fine Step-heights

Effect of Human Finger’s Motion Direction on Tactile Sense in Discriminating Fine Step-heights