Comparison of Supramolecular Aggregate Structure and Spectroscopic and Photoelectrochemical Properties of Tetravalent and Trivalent Metal Phthalocyanine Thin Films

The intermolecular interactions between trivalent metal and tetravalent metal phthalocyanines in vacuum-deposited thin films lead to at least two different crystallite types with different optical and electronic properties. UV-visible, infrared, and Raman spectroscopies, X-ray diffraction, scanning electron microscopy (SEM), and photoelectrochemical metal deposition followed by SEM have been used in combination on the same thin films to characterize these different phases and to differentiate their photoelectrochemical activity. Two distinct crystallite forms are evident from these data, which we hypothesize to be (a) a cofacially stacked linear assembly, aligned along the metal-halide or metal-oxo bond or (b) an assembly where adjacent molecules are staggered to form a slipped-stack arrangement and a unique crystallite in the thin film. This latter stacking arrangement leads to a red-shifted Q band in the visible absorbance spectrum, and these crystallites appear to be photoelectrochemically more active by a factor of at least 10.