Development of highly dichroic fluorescent dyes for less energy-consuming passive-type guest/host liquid crystal display systems

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Passive-type full-color liquid crystal displays(LCDs) consume a large part of the electric power, usually supplied by batteries of limited capacity, for the back light system. The development of less energy-consuming displays is required for their utilization in mobile communication tools. Within this context, fluorescent dye(guest)/LC(host) systems in such displays seem attractive. For their realization it is crucial to develop strongly fluorescent dyes with highly dichroic properties.In this study, various types of symmetric and unsymmetric 4,7-diaryl-2,1,3-benzothiadiazoles having alkoxy, alkoxymethyl, alkoxycarbonyl, ethenyl-and ethynyl groups have been prepared from 4,7-dibrpmo-2,1,3-benzothiazole. All compounds emit strong fluorescence in a solution and in solid state, covering the full color range from blue to red. Their dichroic properties have been evaluated in commercial liquid crystalline media and The dyes show practical dichroic ratios of N>8.0 and possess good solubility in commercial LC media, without destabilisation of the LC phase. With 4,7-bis(p-octyloxyphenyl)-2,1,3-benzothiadiazole as guest dye, a high dichroic ratio in fluorescence of up to 9.1 has been observed in MLC-2039 as the LC matrix.An LCD working model could be fabricated with a mixture of fluorescent dyes in MLC-2039 at a total concentration of 3%(w/w).