Nickel dithiolene dyes

Synthesis and Analysis of Nickel Dithiolene Dyes in a Nematic 246... 

The Liquid Crystal Point Diffraction Interferometer (LCPDI) can be employed to evaluate the Omega Laser system for optimum firing capabilities. This device utilizes a nickel dithiolene infmred absorbing liquid crystal dye dissofved in a liquid crystal host medium (Merck E7). Three nickel dithiolene dyes were characterizedfior both their solubility in the E7 host and their infrared spectral absorption. 

Previous work has shown the nickel dithiolene dye as a desirable candidate for the LCPDl. The nickel dithiolene has a unique aromatic ring structure, which imparts a relatively high infrared absorption and a high thermal and photochemical stability. With 2 alkoxyphenyl substitutions onto the nickel dithiolene core, these complexes possess optical absorbance bands at the desirable wavelength of the laser. However, these alkoxyphenyl substituted compounds have demonstrated limited solubility in the host liquid crystal medium. The potential of an alkyl-phenyl substituents to increase the solubility of the dithiolene dye in the host liquid crystal medium was the primary topic of this investigation. 

Merck E7TM is the liquid crystal host used in the LCPDI device. E7 is a nematic liquid crystal mixture.with a mesophase between -10°C and 60.5°C. The R-group substituents on the nickel dithiolene dye need to be selected for maximum solubility in the E7 host without compromising other important properties (absorption wavelength, optical density or thermal stability). Merck E7 is a room temperature eutectic mixture of cyanobiphenyl and cyanoterphenyl liquid crystal compounds its components are shown in Figure 4. 

The substituted nickel dithiolene dyes are discotic liquid crystals dissolved in the E7 nematic host. There are two molecular components to the nickel dithiolene dye the nickel bis (dithiolene) core and the substituted R groups. The nickel bis (ditholene) core is a unique conjugated transition metal aromatic complex which absorbs near infra-red radiation. 

Several transition metal ions form stable complexes with aliphatic 1,2-dithiols, which absorb in the near-lR. Known as dithiolenes, their nickel complexes in particular have been found to have valuable properties. The physical properties of dithiolenes can be readily tailored by variations on the substituents attached to the dithiols, see (4.13). Although they have low molar absorption coefQcients, when compared to cyanines etc., they do have one big advantage in that they show very little absorption in the visible region." Stracturally analogous dyes can be made from aromatic dithiols and oxothiols (4.14), and the much more bathochromic naphthalene derivatives (4.15), but they are much weaker absorbers. 

Dithiolene complexes, and more specifically the nickel derivatives, are involved in materials used for optical data storage, such as compact disc or laser disc read-only memory (CD- or LD-ROM), and also in copiers or photography related devices. In the latter case, it is the IR-absorbing property that is exploited. Some of these compounds can be found in reviews by Mueller-Westerhoff et al. (353, 354). Recent patents are given as examples in references (458—481). In the field of optical storage, short reviews were published in 1988 (482) and 1990 (362, 483). Here, the dithiolene complexes act as inhibitors of the laser-induced fading of the colored thin layers of the optical discs. They also act as an antioxidant and increase the photostability of the cyanine dyes that constitute the recording layer. Contrary to what was observed for the two... 

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