Photochemistry of Heteroleptic 1,4,5,8-Tetraazaphenanthrene- and Bi-1,2,3-triazolyl-Containing Ruthenium(II) Complexes.

Diimine metal complexes have significant relevance in the development of photodynamic therapy (PDT) and photoactivated chemotherapy (PACT) applications. In particular, complexes of the TAP ligand (1,4,5,8-tetraazaphenanthrene) are known to lead to photoinduced oxidation of DNA, while TAP- and triazole-based complexes are also known to undergo photochemical ligand release processes relevant to PACT. The photophysical and photochemical properties of heteroleptic complexes [Ru(TAP)(btz)] (btz = 1,1'-dibenzyl-4,4'-bi-1,2,3-triazolyl, = 1 (), 2 ()) have been explored. Upon irradiation in acetonitrile, displays analogous photochemistry to that previously observed for [Ru(bpy)(btz)] (bpy = 2,2'-bipyridyl) and generates -[Ru(TAP)(btz)(NCMe)] (), which has been crystallographically characterized, with the observation of the ligand-loss intermediate -[Ru(TAP)(κ-btz)(κ-btz)(NCMe)] (). Complex displays more complicated photochemical behavior with not only preferential photorelease of btz to form -[Ru(TAP)(NCMe)] () but also competitive photorelease of TAP to form . Free TAP is then taken up by to form [Ru(TAP)] () with the proportion of and observed to progressively increase during prolonged photolysis. Data suggest a complex set of reversible photochemical ligand scrambling processes in which and are interconverted. Computational DFT calculations have enabled optimization of geometries of the pro- MC states with repelled btz or TAP ligands crucial for the formation of from and , respectively, lending weight to recent evidence that such MC states play an important mechanistic role in the rich photoreactivity of Ru(II) diimine complexes.