Liquid crystal molecule

A liquid crystal molecule is a long, stiff rod about 2 nanometers long. Between being solid and liquid, rods like these can flow yet still tend to point the same way, like logs floating down a river. That in-between state, the nematic phase, is what an LCD uses.

The backbone is two or three rings of carbon joined end to end, some flat benzene rings and some puckered cyclohexane rings, with a flexible carbon tail at one end. Hydrogen atoms line the rings. The key ingredient for modern displays is fluorine. Fluorine pulls electrons toward itself, so placing it on the rod makes the charge lopsided. In an electric field, the lopsided rod is turned to line up with the field or across it, depending on where the fluorines sit. Fluorinated molecules also resist picking up stray ions, which keeps the picture stable. They're made by multi-step synthesis and heavy purification.

Older molecules used a nitrile (carbon-nitrogen) group instead. George Gray's cyanobiphenyls, made in the UK in the early 1970s, made the first practical displays possible. Fluorinated compounds took over for transistor-driven screens. Each molecule goes into the liquid crystal mixture, blended with others.