The synthesis and visible near-IR region absorption spectra of an 1,6,10,15,19,24,28,33-octaalkylnaphthalocyanine and examples of 3,4,12,13,21,22,30,31-octaalkyl and 3,4,12,13,21,22,30,31-octaalkoxy-2,3-naphthalocyanines are reported.

Graphical AbstractDesign and synthesis of liquid crystalline phthalocyanines: combinations of substituents that promote the discotic nematic mesophase AbstractA homologous series of fourteen metal-free 1,4,8,11,15,18-hexakis(alkyl)-22-methyl-25-hydroxyalkylphthalocyanine derivatives has been investigated to interogate the interlay of the roles of the six alkyl chains and the length of the hydroxyalkyl chain in promoting thermotropic nematic liquid crystalline behavior. All but two of the compounds form mesophases. Eight of the remaining compounds exhibit only columnar mesophases which is common among liquid crystalline phthalocyanines. However, four examples form the rare discotic nematic mesophase. A general structural feature is deduced in that this rare phase is favoured when the number of linking atoms in the hydroxyalkyl chain exceeds twice the number of carbon atoms in any one of the six common alkyl chains, disrupting the columnar packing arrangement. In addition, zinc and copper metallated examples of one of the metal-free discotic nematic compounds were prepared of which the zinc metallated compound formed a nematic phase whereas the copper containing analogue favoured columnar mesophase formation.

A novel homologous series of four 1,4,8,11,15,18-hexakis(pentyl)-22-methyl-25-hydroxyalkylphthalocyanine derivatives with the hydroxyalkyl chain varying from hydroxynonyl through to hydroxydodecyl has been synthesized to investigate the role of the hydroxyalkyl chain in promoting thermotropic liquid crystalline behavior. Polarizing optical miscoscopy reveals that the compound with the shortest hydroxyalkyl chain (hydroxynonyl) exhibits a mesophase with a texture characteristic of a columnar mesophase, common among liquid crystalline phthalocyanine derivatives. However, as the chain is lengthened along the series, there appears a second type of mesophase that shows a schlieren texture. Such a texture is characteristic of a nematic phase and rare among liquid crystalline phthalocyanine derivatives. A fifth compound, the novel 1,4,8,11,15,18-hexakis(pentyl)-22-methyl-25- dodecylphthalocyanine, exhibits only columnar mesophase behavior suggesting that the hydroxyl group at the end of the longer chains of the former compounds is important in developing the nematic phase