Highly Luminescent 4-Pyridyl-Extended Dithieno[3,2-b:2',3'-d]phospholes

The unexpectedly challenging synthesis of 4-pyridyl-extended dithieno[3,2-b:2',3'-d]phospholes via Stille cross-coupling is reported. The optical and electrochemical properties of the phosphoryl-bridged species were studied experimentally and computationally, and their properties were compared with those of their non-P-bridged congeners. The 4-pyridyl-extended dithienophospholes display quantitative luminescence quantum yields in solution and reversible reduction features upon methylation of the pyridine rings. Because of their very high brightness, even in water, 4-pyridyl-extended dithienophospholes are highly promising candidates for new fluorescent probes.