Phthalocyanine and Porphyrin Derivatives of А3B-Type: Quantum-Chemical Modeling of Dimers

A binary system consisting of a mixture of phthalocyanine (Pc) and porphyrin (P) derivatives of the A(3)B-type was studied by the quantum-chemical method (DFT/B97D/6-311G**). Competition of interactions between components of the mixture is considered. For this purpose, a computer simulation of P and Pc monomer structures, as well as dimers Pc...Pc, P...Pc, and P...P was carried out. Several variations of the geometric structure of dimers of each type (Pc...Pc, P...Pc and P...) differing in the mutual orientation of monomers were examined. The values of relative energies and dipole moments of the dimers were calculated. It is shown that during association of P molecules, their orientation in the supramolecular column P...P...P... can be different due to the absence of the preferred direction of resulting dipole moment. In contrast to P, in the Pc...Pc...Pc... columns, a predominantly unidirectional arrangement of Pc monomers with the same orientation of dipole moments is formed. Such individual columns can self-arrange into supramolecular mesophase structures with a certain packing of the columns. For the dimers Pc...Pc, P...Pc and P...P the energies of intermolecular interaction were calculated. It was found that Pc molecules form the most stable dimers with the smallest distance between heterocycles and the highest interaction energy between monomers. Therefore, in the equimolecular system of P and Pc, the Pc...Pc...Pc... column formation will be more preferable. Experimental miscibility investigation of the studied phthalocyanine and porphyrin derivatives confirmed these theoretical conclusions and showed that after heating and subsequent cooling, the mixture of P and Pc (molar ratio of components 1: 1) separates, i.e. in a condensed bulk state the components do not mix. Therefore, it is not possible to obtain homogeneous thin films by spin-coating method. Nevertheless, the creation of thin film materials based on the studied P and Pc in the form of cascade structures with an extended absorption region of the visible part of the spectrum is possible by the Langmuir-Schaefer method. The frontier orbitals calculation showed that in order to create an optimal cascade-type photovoltaic cell, the studied compounds should be deposited onto a substrate according to the lowering of LUMO energy in the following sequence: P / Pc / C-60.