Highly Fluorinated Dithieno[3,2-b:2′,3′-d]phospholes with Stabilized LUMO Levels

A series of dithieno[3,2-b:2′,3′-d]phospholes with a perfluorophenyl substituent at the phosphorus center has been synthesized. Further cross-coupling reactions with additional fluorinated phenyl groups afforded extended conjugated materials with different substitution patterns. Investigation of the optoelectronic properties of the materials revealed smaller highest occupied molecular orbital (HOMO)−lowest unoccupied molecular orbital (LUMO) gaps for the extended materials that were also confirmed by theoretical density functional theory (DFT) calculations. These further indicated that the LUMO levels experience a more significant drop in energy than the respective HOMO levels. This fact can be attributed to the strongly electron-withdrawing nature of the fluoroaryls. In addition, the absolute energies of the frontier orbitals depend on the position of the fluoro substituents in the terminal aryl groups, with meta-positioned fluoro atoms having the strongest effect. Electrochemical investigations as well ...