A theoretical study of conformational aspects and energy transfer between terthiophene and quinquethiophene in perhydrotriphenylene inclusion compounds

A theoretical study of models with supramolecular architecture of co- inclusion compounds based on the host perhydrotriphenylene and guests terthiophene and quinquethiophene (PHTP:T3,T5) is carried out to elucidate in detail the conformational aspects of the oligomeric guest species in the PHTP matrix host. The factors that direct the geometry, location and separation of terthiophene and quinquethiophene within the channels of the PHTP host have been studied using semi-empirical and ab initio calculations. The movement of the guests inside the channel is subject to constraints preventing free rotations or axial displacements along the nanochannel. Optimal arrangement and the general trend of the relative order between T3 and T5 in the (PHTP: T3, T5) co- inclusion compound is obtained. Furthermore, excited state calculations allow the explanation of the spectral shifts of the included species in terms of the planarization of their geometries. An analysis of the energy transfer processes between the T3-T5 donor-acceptor pair based on the configurational details of the co- inclusion compound conclude that efficient transfer proceeds only through two different and perpendicular windows for the T3 -> T5 transfer. The results emphasize the importance for better understanding of the directional details of the energy transfer mechanisms in this kind of one-dimensional systems.