The new ligands 4′-(2,5-dimethoxyphenyl)- (L¹), 4′-(2,5-hydroxyphenyl)- (L²) and 4′-(1,4-benzoquinonyl)-2,2′∶6′,2″-terpyridine (L³) and a range of their transition-metal complexes have been prepared. The crystal and molecular structures of L¹ and [CuL¹₂][PF₆]₂ have been determined. Model reactions showed that the complexes [ML²₂]ⁿ⁺ can be derivatized with suitable organic reagents, suggesting they may be incorporated into multicomponent architectures using either ester or ether linkages. The chromophoric, magnetic and electrochemical properties of the complexes vary with transition metal and 4′ substituent. The hydroquinonyl-substituted [ML²₂]²⁺ and the quinonyl-substituted [ML³₂]²⁺ complexes can be electrochemically interconverted in the presence of weak acid and switching between hydroquinonyl and quinonyl 4′ substituents can significantly perturb physical properties of the bis(terpyridyl) transition-metal centre(s).