Synthesis, phase behaviour and polymerisation of mesogenic materials based on 3-substituted pyrroles

Abstract

Synthetic routes which lead to the formation of 3-substituted pyrroles with mesogenic units are described. Two particular compounds have been prepared: 3-{6-[4-(4-methoxyphenylazo)phenoxy]hexyl}pyrrole and 3-[6-(4′-cyanobiphenyl-4-yloxy)hexyl]pyrrole. Both exhibit monotropic liquid crystalline phases, and for the latter compound the stability of the mesophase observed could be increased by incorporation of a small amount of a commercially available liquid crystal. Electrochemical investigations show that the azobenzene based material is a poor candidate for the formation of polypyrrole derivatives, because of the ease with which competing oxidative processes occur. The cyanobiphenyl derivative, in contrast, has been polymerised electrochemically to form electrically conducting polymer films; these films reveal an electrochromic effect by virtue of reversible doping. It has also proved possible to polymerise this material chemically to give a polymeric material which is soluble in a variety of solvents. A further procedure involved oxidation with bromine vapour to polymerise the material in an aligned state; the yields of such polymers, however, are poor, and considerably lower than those obtained for materials prepared in the isotropic melt.