Spectroscopic and X-ray diffraction study of Langmuir–Blodgett films of some 1,4,8,11,15,18-hexaalkyl-22,25-bis(carboxypropyl)phthalocyanines

Abstract

Molecular assemblies within Langmuir–Blodgett (LB) films of 1,4,8,11,15,18-hexaoctyl-22,25-bis(carboxypropyl)phthalocyanine (1a) copper 1,4,8,11,15,18-hexanonyl-22,25-bis(carboxypropyl)phthalocyaninate (1b) and 1,4,8,11,15,18-hexadecyl-22,25-bis(carboxypropyl)phthalocyanine (1c) 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 1a and 1b 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 1a but occurs over a wide temperature range for the film of 1b. Heating the film of 1c to 140 °C modifies the packing but in this case a further modification occurs on cooling.