Synthesis, electrochemistry and photoexcited-state properties of dinuclear ruthenium complexes bridged by 2,6′-bis(2-pyridyl)-2,2′:6,2″-thiazolo[4,5- d]-benzothiazole

Abstract

The new bridging ligand, 2,6′-bis(2-pyridyl)-2,2′:6,2″-thiazolo[4,5- d]-benzothiazole (bptb) and its dinuclear Ru complexes have been synthesized. The combination of the transient absorption (TA) spectra and spectroelectrochemical difference spectra has led to the assignment of the lowest excited state for the dinuclear Ru(II) complexes as a Ru-to-bptb charge transfer state. Although the ab initio molecular calculations of bridging ligands have provided lower HOMO/LUMO energies for bptb compared to those of 2,6-bis(2-pyridyl)benzodiimidazole (dpimbH 2), the degree of electronic coupling for the dinuclear bptb complex is smaller than that for the dpimbH 2 complex from the analysis of intervalence charge transfer band. Since both dinuclear Ru complexes have a similar coordination environment, the Ru dπ-HOMO Lπ mixing is dominant for the metal-metal interaction through the hole transfer mechanism.