The monolayer and LB film-forming properties of 20 structurally related amphiphilic octa-substituted phthalocyanine derivatives have been assessed. The molecular packing within examples of the films has been probed by visible-region spectroscopy and low-angle X-ray diffraction methods. Among derivatives where the aliphatic substituents are attached by ether linkages, there is a variation in the behaviour according to the length of the chains and whether or not the chains are branched. Films are not highly ordered but may contain domains of ordered structure, giving rise to r i redshifted absorption band in the visible spectrum. Analogues where the chains are attached by carbon-carbon bonds show superior monolayer behaviour and are excellent materials for deposition as LB films. Furthermore, there is good evidence from the spectra that change in the length of the alkyl chains provides a means of controlling the type of molecular packing within the films.

Molecular assemblies within Langmuir-Blodgett (LB) fi Ims of 1,4,8,11,15,18-hexaoctyl-22,25-bis(carboxy-propy1)phthalocyanine (la) copper 1,4,8,11,15,18-hexanonyl-22,25-bis(carboxypropyl)phthalocyaninate (lb) and 1,4,8,11,15,18-hexadecyl-22,25-bis(carboxypropyl)phthalocyanine (lc) have been examined using X-ray diffraction, RAIRS and polarised optical spectroscopy. The LB films are constructed as bilayers by Y-type deposition and the resulting assemblies give rise to visible-region absorption spectra closely similar to those of crystallised films of octaalkylphthalocyanines. When heated, the molecular assemblies within the LB films of l a and l b reorganise irreversibly to a form in which the bilayer spacing is reduced. The transition from one type of packing to another is sharp for the film of l a but occurs over a wide temperature range for the film of l b . Heating the film of l c to 140°C modifies the packing but in this case a further modification occurs on cooling.

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