Synthesis and characterisation of some mesogenic mononuclear and multinuclear phthalocyanines

Octa-substituted phthalocyanines carrying either one or two hydroxyalkyl chains have been synthesised and their liquid crystalline behaviour characterised by polarised light microscopy and differential scanning calorimetry. The compounds form discotic columnar mesophases with hexagonal or rectangular symmetry. Examples have been used as precursors for the synthesis of mesogenic di-nuclear and tri-nuclear phthalocyanines, ie derivatives containing two or three phthalocyanine rings. These compounds have been characterised by elemental analysis and low resolution field desorption mass spectrometry, ED-MS. H-1 NMR spectroscopy and gel permeation chromatography of selected examples provide supporting data. Visible region spectroscopy of dilute solutions of the multinuclear phthalocyanines in cyclohexane (down to a concentration of 5 x 10(-7) mol dm(-3) where intermolecular aggregation is expected to be minimal) suggests that the compounds exist as an equilibrium between a 'closed' conformer where the two rings are arranged cofacially (broad band centred at ca 645nm) and an open form having an absorption band similar to that of the simpler precursor phthalocyanines, lambda(max) ca. 730 nm. The closed conformer is favoured in more polar media eg 10% toluene - 90% ethanol. Examples have been deposited as spin coated films of even thickness on glass slides.