Asymmetrical diacetylenes with a pyridine ring bonded directly to one end of the diacetylene unit and an aryl system containing a flexible alkoxy chain at the opposite end, have been synthesized and show liquid crystalline behaviour. The mesophase behaviour is shown to be dependent on the length of the flexible alkoxy chain. Incorporation of one of these diacetylenes in a polymer ‘guest-host’ system at a 15 wt% concentration gave a high X(2)non-linear optical susceptibility of 4.27 × 10−9e.s.u.