Helichromic-smectic liquid crystal compositions and display cells

A thermally addressable liquid crystal display device having no auxiliary polarizers, which provides a high contrast image against a background comprising:

• a layer of a composition consisting essentially of a liquid crystal medium in admixture with an organic, nonionic, nonliquid-crystalline helichromic compound, said layer disposed between a top substrate and a bottom substrate, said helichromic compound being soluble in said liquid crystal medium, said helichromic compound being a circularly dichroic dye, and said helichromic compound having the general formula
• Q(Z).sub.n
• wherein
• Q is an organic group having a chromophoric character;
• Z is an optically-active organic group;
• and
• n is an integer having a value of 1 or greater;
• said liquid crystal medium being thermally sensitive and having a transition between at least two thermal phases, an upper phase being a nematic phase and a lower thermal phase being a smectic phase, said mixture having two possible states of orientation in said smectic phase, a first orientation state being substantially light absorbing and a second state being substantially light transmissive;
• a means of affecting a thermal transition between said lower thermal phase and said upper thermal phase;
• and
• a means of electrically addressing portions of said mixture to develop said second light transmissive state when said mixture passes rapidly into said lower thermal state from said upper thermal state, the remaining unaddressed portions of said mixture developing said first substantially light absorbing state when said mixture passes rapidly into said lower thermal state from said upper thermal state.