Highly luminescent terpyridinyl-ethynyl functionalized dithieno[3,2-b:2′,3′-d]phospholes: synthesis, properties and complexation behavior

The synthesis and advanced characterization, as well as the complexation behavior of a series of terpyridinyl-ethynyl substituted dithieno[3,2-b:2',3'-d]phospholes is reported. The functionalization of the dithienophosphole core furnishes the system with suitable ligand properties for a variety of transition metal centers (Zn2+, Ru2+, Pt2+) to form the corresponding complexes. The terpyridinyl-extended ligand systems show pronounced photoluminescence features that are beneficial for the formation of strongly luminescent transition metal complexes potentially to be employed in organic light emitting electrochemical cells. Theoretical calculations support the strong luminescence of the ligands resulting from pi-pi* transitions involving the extended pi-conjugated scaffold. The ligands were found to exhibit remarkable luminescence stability towards protonation, whereas complexation to transition metals shows distinct changes in the photophysical properties that depend of the nature of the transition metal employed.