Modulation of Electrochemical and Spectroscopic Properties in Ru(II)-Terpyridyl End-Capped Homobimetallic Organometallic Complexes by Varying pi-Conjugated Organic Spacers

A series of wire-like binuclear Ru(II) complexes, 10-13, of general formula [(tpy-C6H4-Me)(PPh3)(2)Ru-C equivalent to C-Ar-C equivalent to C-Ru(PPh3)(2)(tpy-C6H4-Me)](2+), (tpy-C6H4-Me=4 '(4-tolyl)-2,2 '-6 ',2 ''-terpyridyl; Ar=thienyl, phenyl, benzothiadiazolyl and fluorenyl respectively) have been judiciously designed, developed and characterized by various spectroscopic tools. The aromatic bridging moieties have been varied systematically to tune not only the chain length but also the electronic nature of the spacer units. To understand the intermetallic electronic properties, electrochemical and UV-Vis-NIR spectroscopic studies have been explored. Electrochemical studies reveal reversible redox waves for 10, and quasi-reversible to irrreversible redox waves for 11-13 in the region of 0.30-0.60 V and 0.55-0.75 V (with respect to reference electrode of Ag/AgCl), presumably due to successive one electron oxidation of the Ru(II) conjugates. Interestingly, complexes 10 and 11 show promising NIR absorption (epsilon in order of 10(3) M(-1)cm(-1)). Electron transfer in the diruthenium wire-like complexes can be perturbed to different extent by varying the spacer units. The computational studies (DFT and TDDFT) further support the structure property relationship, electrochemical and spectrsopic properties which is mediated through the participation of the bridging ligand in the corresponding mono-oxidized organometallic wire-like complexes.