Rewritable full‐color recording on a thin solid film of a cholesteric low‐molecular‐weight compound

Abstract

Full-color recording is technologically important not only for the storage and reproduction of color information but also for the enhancement of recording density without a reduction in the size of one unit area by utilizing the spectrum of light for recording and reading memories, as in photochemical hole burning. Although full-color "writeonce" recording media (e.g., photographs and photocopiers) or rewritable "on-and-off" recording media (e.g., magnetic, opto-magnetic, and thermo-optic recordings) are well developed, rewritable full-color recording has still not been realized. This can be attributed mainly to the difficulty of finding thermally stable materials that change color reversibly under the action of external stimuli. Here we present a cholesteric low-molecular-weight compound that, in the form of a thin solid film, shows stable iridescent colors in the visible region. The color of the compound is totally, partially, or in an imagewise manner changed into selected colors by thermal treatment above 87°C. Compounds with this property should find applications as highdensity memory media that use the spectrum of light or as thermo-sensitive full-color recording materials.Cholesteric color has fascinated people since the discovery of liquid crystals.''] The ability to change the cholesteric colors over the whole visible region by stimuli such as temperature, pressure, and electric field is important from not only a scientific but also a practical point of view. On the other hand, fixing of specific colors, namely colors insensitive to stimuli, is also attracting much attention in connection with the iridescent colors of a jewel beetle''] and for applications such as optical filters for selective reflection or large optical rotation. Polymeric materials have already been used to obtain thermally insensitive solid films with cholesteric str~cture.[~-~] High viscosity or three-dimensional networks of polymer chains practically fixes the pitch of the helical configuration of polymers, which determines the colors of cholesteric liquid crystalline compounds, providing a thermally insensitive cholesteric color. Although it is also possible to tune the color, by changing the monomer ratio in copolymer^,[^'^] by changing the temperature during photopolymerization of cholesteric monom e r~, '~] or by changing the ratio between polymerizing solution and lyotropic reversible and fast switching of the cholesteric color, which is desired for applica-tions as rewritable memory or recording media, is impossible to achieve with these polymeric materials. A low-molecular-weight cholesteric compound that we recently synthesized shows, in the solid state, changeable iridescent colors that can be selected from the whole visible region by thermal treatment.The cholesteryl derivative 1 (Scheme 1) was synthesized by condensation of cholesterol and the corresponding diacid in the presence of dicyclohexyl carbodiimide and 4-dimethylamiriopyridine in dichloromethane. This compound, 0 Scheme 1. Chemical structure of cholesteryl deriv...

Cholesteric Liquid Crystals for Color Information Technology

“…In addition, the color of the solid can be controlled and selected from the entire visible region. [31,32] The dicholesteryl ester 4-8 (see Fig. 6) obtained as a white powder after recrystallization exhibits a cholesteric phase showing various iridescent colors from blue to red via green on cooling, depending on the temperature and the cooling rate below 115 C. When the compound showing iridescent colors was quickly cooled down to 0 C by dipping in ice-water, it solidified while maintaining the iridescent color observed at the higher temperature at which the quick cooling started (Fig.…”

Synthesis and properties of helical aliphatic polyacetylene containing a cholesteryl group in the side chain

“…[6] The use of the cholesteryl group as a chiral substituent in the side chain is of interest in terms of the optical properties to induce the helical structure which could be applied in such optoelectronics fields as image recording, high-density storage, and optical elements for high-power laser systems. [7] This paper describes the structural analysis and properties of aliphatic polyacetylenes containing cholesteryl groups varied in the number of methylenes in the spacer group, which were polymerized with Rh complex catalysts.…”

Approaches to mimic the metallic sheen in beetles

“…Tamaoki and colleagues reports on a cholesteryl-based temperature-sensitive CLC where the colour change takes place over a temperature range from 87-115 degree Celsius [13,14]. By quenching the compound in ice water from a certain temperature the 'frozen' solid can keep its colour.…”

“…They describe how a CLC that is cholesteric in the temperature range 87-115 degree Celsius can be heated and quenched resulting in a range of different colours. The material can be used for rewritable full colour media [13,14].…”