Quantum Chemical Design Of Multifunctional Materials Based On Tris(O-phenylenedioxy) Cyclotriphosphazene (TPP)

The absorption properties of materials are emerging as a forefront issue of present-day research, mainly due to the strategic industrial and environmental applications such as gas storage, selective gas recognition, and separation. In this field, the van der Waals (vdW) organic zeolite based on TPP and molecular assembled materials constitute a competing alternative and are thus still to be extensively explored. The molecular crystal of TPP, which exhibits permanent nanoporosity, was reported to be able to store large amounts of carbon dioxide and methane selectively over nitrogen, oxygen, and hydrogen, suggesting intriguing applications for fuel storage, hydrogen purification, and carbon dioxide removal from the air. Although a number of computational reports can be found from the literature on phosphazenes, a few was dedicated to the organic zeolite use of the new family of materials for which, a deep understanding seems to be needed prior to a computational design, and/or any other work, towards the development of this kind of materials. This thesis was conceived for this issue.First, the host-guest interactions between methane, carbone dioxide, nitrogen or hydrogen and TPP are investigated with the aid of modern methods. In agreement with experimental observations already reported, CO₂ and CH₄ were shown to be preferentially absorbed in the one layer tunnel, with the first being pushed closer one of the three phenyl ring of the walls, and the CH₄ at a site where the carbon is located at an equal distance from the centers of the three rings. N₂ was found to be preferentially adsorbed in the same site as CO₂, the H₂ adsorption site being located in the interlayer region of the zeolite. On the basis of our results, the interaction energy between the host TPP and the guest molecules was predicted in the increasing order of TPP-H₂ < TPP-N₂ < TPP-CH₄ < TPP-CO₂. The extremely weak interactions for the first two adducts were used to explain the selective adsorption of CH₄ and CO₂ (whose interaction energies are far greater) over N₂ and H₂.In a second step, molecular structures and electronic properties were investigated for a series of TTF-like fragments containing systems using theoretical methodologies based on density functional theory (DFT) and Hartree-Fock approaches. We mainly concentrated our study on the role of TTF framework and that of a substituted central ring, while the role of the bridging moiety was also studied. Judged from the calculated ionization potentials and Highest Occupied Molecular Orbital (HOMO) energy point of view, it was found that substituting [(PN)₃] in TPP with [(CO)₃], [(CS)₃], or [(CNH)₃] rings and the side fragment with half TTF-like fragment may lead to a series of derivatives showing a electron-donor strength comparable or better than the one for the commonly known electron-donors (E-D). In addition, a new series of candidates for organic superconductors were designed, based on the TTF-like extension of TPP side fragment and both partial and total O/S (O/NH or S/NH) substitution. More interestingly, the last group was predicted to combine a good E-D strength and the"paddle wheel"molecular shape responsible for inclusion adducts formation, with the O/NH substituted derivatives showing better E-D ability. From this series of derivatives, tunnels of variable diameter can then be awaited depending on the side group used. This is important since it can provide ease in modulating the conducting properties by intercalation of judiciously chosen acceptors.Finally, the last step sheds some light on the CH/N substitution along with the enhancement ofÏ€-conjugation effect on the zeolite TPP structures and properties. Our results revealed that the CH/N substitution preserves the"paddle wheel"molecular shape, a key factor in the tunnel formation on which is based the use of TPP and TPP-like molecules for OZ use. A significantly great increase in the E-D capacity owing to the enhancedÏ€-conjugation through a linear or lateral extension with an aromatic ring was also found, the lateral extension being shown to induce the most significant E-D capacity. The features revealed in the chapter indicated that the E-D capacity of TPP can be easily tuned by both the CH/N hetero-substitution and the lateral or linear extension of the side group with one or two aromatic rings. This may provide a way to modulate the stability of some guest...host complexes (by varying the E-D strength of the side group) and the amount/size of the adsorbate (through the length variation of the side group).