Structure-Property Studies of Bichromophoric, PAH-Functionalized Dithieno[3,2-b:2′,3′-d]phospholes

A series of dithienophospholes featuring polyaromatic hydrocarbon (PAR) substituents, with increasing number of fused rings ranging from 2 to 4 at the phosphorus center, have been synthesized and characterized. The installation of a large pi-system in the vicinity of the dithienophosphole scaffold was found to induce unusual photophysics for this system that are based on the creation of two neighboring chromophores within the same molecular scaffold. Extensive photophysical studies revealed that significant energy transfer (ET) occurs from the PAH unit, which acts as a donor, to the dithienophosphole acceptor, showing ET efficiencies of almost 90%. TD-DFT calculations confirm the possibility for the two subunits to communicate with each other. Furthermore, due to the presence of the out-of-plane dithienophosphole unit, the PAR species do not show any significant tendency to form aggregates, such as excimers/exciplexes, even in colloidal suspensions.