novel liquid crystalline compounds having low viscosity , low transition temperatures , positive dielectric anisotropy and extremely low optical birefringence are provided . the compounds are represented by the formula : ## str1 ## where r and r 1 can be the same or different straight chain alkyl or alkoxy group and m can be 1 or 2 . guest - host electrooptical displays including a mixture of one or more of the compounds with a suitable pleochroic dye exhibit much improved constrast and low driving voltage while eliminating the need for polarizers and excessive dye additions .