Folding oligomers of difluorinated thienylfurans: a DFT study

Density functional theory calculations were performed on a series of difluorinated-thienylfuran oligomers containing up to six repeat units. For any given oligomer, a building unit was chosen to be either in the transoid or in the cisoid conformation. The oligomers are found to be more stable in the all-cisoid conformation as a result of intramolecular F...H hydrogen bonding interactions, as well as stacking pi-pi interactions for the larger oligomers. The relative stability increases markedly with the size of the oligomers, allowing for the adoption of well-defined folding helical patterns for systems with at least five repeat units. Conveniently designed isodesmic reactions show that folding of the oligomers is a thermodynamically favorable process.