Synthesis and film-forming properties of metal complexes of octadecyl ethers of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin

Abstract

Metal complexes [Al^III, Fe^III, Co^II, Ni^II, Cu^II, Zn^II, Cd^II, and Pt^II] of various octadecyl ethers of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin have been prepared and characterised. The metalloporphyrins are examined for their ability to form layers using the Langmuir technique, and pressure–area isotherms are presented. Multilayers on glass substrates are made in suitable cases using the Langmuir–Blodgett method. Complexes of the tris(octadecyl) ether generally give films with favourable properties although the aluminium(III) complex, which is shown to be dimeric, does not. In certain cases where the pure metalloporphyrin gives unsatisfactory results, the film can be improved using a stabiliser such as stearic acid. The absorption maxima of the films are determined before and after exposure to sensor gases (Cl₂, HCl, NO₂) and after further exposure to hydrazine vapour (‘hydrazine reset’), and compared with solution spectra.