Design of TTF-based phosphazenes combining a good electron-donor capacity and possible inclusion adduct formation

The physical properties of porous material can be modulated by intercalation of small molecules, whose size, in the case of tris-o-phenylenedioxy) cyclotriphosphazene (TPP)-based materials, vary with the different side groups. Starting from the TPP structure, a series of new derivatives were constructed through the core ring [(NP)(3)] substitution by [(CNH)(3)], [(CO)(3)], and [(CS)(3)] or/and the side group substitution by tetrathiafulvalene and a series of related fragments including bis(ethylenedithio) tetrathiafulvalene, 2-methylene-1, 3-dithiole, and 2-methylene-5,6-dihydro[1,3]dithiolo[4,5-b][1,4]dithiine. In the side fragment, such a substitution corresponds to the replacement of a ring heteroatom, an addition of substituents, or both. With use of theoretical methodologies based on DFT-B3LYP/6-31G* and HF/6-31G**//B3LYP/6-31G* approaches, molecular geometries and electronic properties including the LUMO and HOMO energies, the HOMO-LUMO gap, as well as the ionization potential (IP) were calculated. In comparison with the commonly used organic superconductors, most of the molecules investigated were predicted to show comparable or better electron-donor strength. Interestingly, a number of cyclophosphazene [(NP)(3)]-containing compounds were predicted to show the "paddle wheel" shape responsible for inclusion adducts formation, making these compounds to be potential candidates for organic superconductors with the ease of modulating their conducting properties by intercalation of suitable acceptors.