Binuclear Ruthenium Complexes with Benzo[1,2-b;4,5-b′]-dithiophene Analogues as Bridge Ligands: Syntheses, Characterization and Notable Difference on Electronic Coupling

Diruthenium ethynyl complexes 1-3 (1: 1,5-dithia-s-indacene-4,8-dione; 2: 4,8-diethoxybenzo[1,2-b:4,5-b']dithiophene; 3: 4,8-didodecyloxybenzo[1,2-b:4,5-b']dithiophene) have been synthesized by incorporating the respective conjugated heterocyclic spacer and characterized by NMR and elemental analysis. The effects of bridge ligands' properties on electronic coupling between redox-active ruthenium terminal groups were investigated by electrochemistry, UV/vis/near-IR and IR spectroelectrochemistry combined with density functional theory (DFT) and time-dependent DFT calculations. Electrochemistry results indicated that complexes 1-3 exhibit two fully reversible oxidation waves, and complexes 2 and 3 with electron-rich and pi-conjuagted bridge ligands are characterized by excellent electrochemical properties. Furthermore, the larger v(C C) separation from the IR spectroelectrochemical results of 2 and 3 and the intense NIR absorption features of singly oxidized species 2(+) and 3(+) revealed that their molecular skeletons have superior abilities to delocalize the positive charge. The spin density distribution from DFT calculations proved the conclusions of this study.