Alkyne substituted mononuclear photocatalysts based on [RuCl(bpy)(tpy)]⁺

The ethynyl-phenylene substituted 2,2':6',2''-terpyridine (tpy) derivatives, 4-(phenyl-ethynyl)-2,2':6',2''-terpyridine (L(1)), 4-(methoxyphenyl-ethynyl)-2,2':6',2''-terpyridine (L(2)), 4-(tolyl-ethynyl)-2,2':6',2''-terpyridine (L(3)) and 4-(nitrophenyl-ethynyl)-2,2':6',2''-terpyridine (L(4)) have been used to synthesize four new [RuCl(2,2'-bipyridine)(L(n))]PF6 based complexes. Electronic absorption, resonance Raman, cyclic voltammetry and spectroelectrochemistry aided by DFT calculations were used to explore the influence of the alkynyl substituents on the electronic structures, photochemical and redox properties of the complexes. Furthermore, it is shown that the addition of ethynyl phenyl moieties to the 4-position of the tpy ligand does not have a detrimental effect on these complexes, or the analogous aqua complexes, with respect to their ability to photocatalyse the oxidation of 4-methoxybenzyl alcohol to the corresponding benzaldehyde.