Formation of two-dimensional (M) and three-dimensional (V) nanoaggregates of substituted cobalt porphyrin in the Langmuir layers and Langmuir-Schaefer films

Floating molecular layers of cobalt tetra(p-metoxyphenyl)porphyrin (CoTMPP) were studied experimentally and theoretically. The structure of the layers was analyzed within the framework of an original model and method for quantitative analysis of compression isotherms of a monolayer comprised of Major nanoaggregates (M-monolayer). The existence regions as well as the structural parameters and properties of monolayers in stable states were determined. These include the size of M-nanoaggregates and the number of molecules in them, the distance between aggregates, the content of bound water and water between aggregates, the compressibility, and the pressure and current surface concentration ranges corresponding to stable states. Quantitative correlations between the fabrication conditions, nanoaggregate size, and properties of M-monolayers were obtained. The state diagrams and M-isotherms were plotted and a passport of CoTMPP floating layers was compiled. A classification of porphyrin M-monolayers including the description of rarefied and condensed M-aggregates in the floating monolayers was proposed; a quantitative model for such monolayers was developed. Constants governing the structure of CoTMPP monolayers and the formation conditions of stable floating layers with 3D nanoaggregates (V-nanoaggregates) were determined. A specific feature of CoTMPP which can discriminate it from azaporphyrins is as follows: the size of M (edge)-aqua aggregates and the distance between them are independent on the initial surface concentration. CoTMPP thin films on solid substrates were prepared by various methods including the Langmuir-Schaefer technique. A comparison of UV-Vis spectra of the solution, Langmuir-Schaefer films, and spin-cast films suggests different degrees of CoTMPP aggregation in these systems.