The self-ordering properties of novel phthalocyanines with out-of-plane alkyl substituents

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.