Octadecyl ethers of 5,10,15,20-tetra(4-hydroxyphenyl)porphyrin: synthesis and film-forming properties

The alkylation of 5,10,15,20-tetrakis(4-hydroxyphenyl)porphyrin with octadecyl bromide in the presence of anhydrous potassium carbonate in dimethyiformamide gives a mixture of substitution products, polysubstitution predominating when a large excess of alkylating reagent is used. When the products were subjected to column chromatography, the 5-(4-octadecyloxyphenyl), the 5,10- and 5,15-bis(4-octadecyloxyphenyl), the 5,10,15-tris(4-octadecyloxyphenyl) and the 5,10,15,20-tetrakis(4-octadecyloxyphenyl)porphyrin derivatives were separated and identified. Langmuir film formation is reported for these substances, and pressure–area isotherms are presented. Multilayers (20 layers) of some of these compounds were exposed to test gases (Cl₂, NO₂, HCl) and the multilayers were reset with hydrazine vapour. Apart from evidence for incomplete gas penetration into the multilayer assembly under the conditions employed, the electronic spectra of the solid films correlate closely with the corresponding solution spectra.