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‐diethoxybenzo1,2‐b:4,5‐ b']dithiophene; 3 : 4,8‐didodecyloxybenzo1,2‐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 π‐conjuagted bridge ligands are characterized by excellent electrochemical properties. Furthermore, the larger ν(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.