Electrochemical and Photophysical Study of Homoleptic and Heteroleptic Methylated Ru(II) Bis‐terpyridine Complexes

Abstract In this study, we investigate the impact of N ‐methylation on the electronic and photophysical properties of both homoleptic and heteroleptic Ru(II) bis‐terpyridine complexes based on the recently reported ligand 4’‐(4‐bromophenyl)‐4,4’’’ : 4’’,4’’’’‐dipyridinyl‐2,2’ : 6’,2’’‐terpyridine (Bipytpy), with pyridine substituents in the 4‐ and 4’’‐position. The first reduction of the methylated complexes takes place at the pyridinium site and is observed as multi‐electron process. Following N ‐methylation, the complexes exhibit higher luminescence quantum yields and longer excited‐state lifetimes. Interestingly, the photophysical properties of the heteroleptic and homoleptic complexes are rather similar. TD‐DFT calculations support the experimental results. Furthermore, the complexes are tested as photosensitizers for photocatalytic hydrogen production, as the parent complex 1 [Ru(Bipytpy)(Tolyltpy)](PF 6 ) 2 (Tolyltpy: 4′‐tolyl‐2,2′ : 6′,2′’‐terpyridine) was recently shown to be active and highly stable under photocatalytic conditions. However, the methylated complexes reported herein are inactive as photosensitizers under the chosen conditions, presumably due to loss of the methyl groups, converting them to the non‐methylated parent complexes.