Uniform thin ®lms are needed for the exploration and exploitation of the fascinating optical and electronic properties of the phthalocyanine (Pc) macrocycle. Spin-coating has been demonstrated to be a simple, fast and reproducible method of fabricating uniform ®lms. However, solubility in a volatile organic solvent is a prerequisite for this technique and previous studies have shown that groups placed on the Pc macrocycle can have a profound effect on the nanoscale structure of the resulting ®lm. In this paper we attempt to establish some fundamental structure±property relationships which determine the molecular packing within such ®lms. Previous studies are reviewed and the ®lm forming properties of a number of Pc derivatives are examined. In particular, the formation of ®lms in which the Pc cores are isolated from each other by the use of novel, sterically crowded hexadeca-substituted Pcs is examined.

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Two novel homologous series of phthalocyanines were prepared from 2,2‐dialkylindane and 2,2‐dialkyl‐1,3‐benzodioxole precursors. It was anticipated that attaching alkyl chains to five‐membered rings, fused to the peripheral sites of the phthalocyanine ring, would result in the adoption of an out‐of‐plane configuration and thereby discourage cofacial aggregation, to provide an analogy with picket‐fence porphyrins. This strategy proved partially successful. Some members of the series of phthalocyanines derived from 2,2‐dialkyl‐1,3‐benzodioxoles, in which the alkyl chains are linked to the phthalocyanine via a cyclic ketal, form spin‐coated thin films in which the phthalocyanine cores are perfectly isolated. This behaviour is associated with the formation of a disordered crystal that appears as a mesophase in the thermal profile of these materials. However, the phthalocyanines derived from 2,2‐dialkylindanes display a columnar mesophase over a wide temperature range, with some liquid crystalline derivatives at ambient temperature. A single‐crystal X‐ray diffraction structure of the octahexyl derivative of this series shows how the columnar assembly accommodates the out‐of‐plane alkyl chains by tilting the macrocyclic plane of the phthalocyanine components with respect to the axis of the column. This study helps to emphasise the importance of both the steric and electronic effects of substituents on the packing behaviour of phthalocyanines in the condensed phase, and especially the role of electron‐donating oxygen atoms directly attached to the ring.

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Phthalocyanine (Pc) derivatives in which substituents hold the Pc units in isolation from one another in the solid state are potentially useful materials. Three synthetic approaches to achieve this goal are described: the construction of a dendrimer about a Pc core; the incorporation of alkyl side chains which are forced to lie out of the plane of the macrocycle; and the synthesis of sterically crowded hexadeca-substituted derivatives. The effectiveness of each of these strategies is readily measured by comparing the visible absorption spectrum of a spin-coated film with that obtained from the non-aggregated Pc in dilute solution. These studies show that the size of the substituents is of secondary importance for their efficiency in inducing Pc isolation. Of more importance is the substituents' adopted position relative to the Pc ring.