Infra-red spectra of phthalocyanines with different central metal atoms

Abstract

In a series of investigations of absorption spectra, of the fluorescence and photoelectric phenomena of the phthalocyanines in the visible range, a marked sensitivity has been observed towards the presence of small concentrations of some O- and N-containing molecules, which are capable of forming a co-ordinative bond with the central metal atom in these pigments. In order to explore the details of such a molecular interaction, we investigated the vibration spectra of phthalocyanines in the infra-red (4000-700 cm −1) and especially the influence on these different compounds in the gaseous state. Thin (0·01 mm thick) layers of the pigments have been used, obtained by sublimation in vacuo. The layers were highly porous. Molecules of different behaviour (electron donors and bases) were brought in contact as vapours with the phthalocyanine layers in vacuo, viz. H 2O, D 2O, H 2S, hydrazine, phenyl hydrazine, ammonia, benzylamine, pyridine, aniline, diphenylamine, indole, oxygen and others. The addition of these molecules to the phthalocyanines was spectrally revealed by a shift of the infra-red bands of the added molecules, in specified cases, as compared with their position in the free gaseous or dissolved molecule in a neutral solvent. Moreover in these cases the addend could not be removed by simple evacuation and freezing out without heating, as could be judged from the spectrum. On addition the whole infra-red spectrum of the phthalocyanine structure was also changed in a characteristic manner, depending on the nature of the added molecule, and as well on the central metal atom. Phthalocyanine without metal does not exhibit any change on contact with the vapours of all the compounds indicated above. This means that the interaction is exerted through the intermediary of the central metal atom. From these spectral data the most active centres for addition in the phthalocyanines are Mg, Zn, Fe. The central Cu atom was far less able to add the same molecules, as could be judged from the spectra.