Two Ru^II Linkage Isomers with Distinctly Different Charge Transfer Photophysics

Abstract

The ligand PHEHAT (PHEHAT = 1,10-phenanthrolino [5,6-b]1,4,5,8,9,12hexaazatriphenylene) presents a structural asymmetry that has a dramatic influence on the photophysical properties depending on the chelation site of the metal ion in the linkage isomers. While [Ru II (phen) 2 HATPHE] 2+ behaves classically, like [Ru II (bpy) 3 ] 2+ , [Ru II (phen) 2 PHEHAT] 2+ exhibits an unusual behaviour. It appears that this complex has two 3 MLCT bright states, the lower one being weakly emissive or non-emissive depending on the solvent and temperature. Different photophysical techniques involving a wide range of various temperatures and timescales are essential to analyze this difference. A full photophysical scheme is proposed based on experimental data and DFT calculations. While previous studies focused on high temperatures and longer timescale emission, we explore the complexes at very low temperatures and very short times in order to obtain a more complete picture of the intriguing photophysical behaviour of these complexes.

Synthesis of Ru(ii) and Os(ii) photosensitizers bearing one 9,10-diamino-1,4,5,8-tetraazaphenanthrene scaffold

“…24,25 A common interest however, for many photosensitizers, earth abundant and rare, is the development of ligands with extended π-systems or with the ability to bridge a second metal center. [26][27][28][29][30][31][32][33][34][35][36][37][38] For example, in biomedical applications, intercala-tion within DNA or photoreaction with DNA bases was made possible with transition metal complexes (Ru, Rh, Os) carrying extended ligands such as TPPHZ (tetrapyrido[3,2-a:2′,3′-c:3″,2″h:2′′′,3′′′-j]phenazine), dppz (dipyrido[3,2-a:2′,3′-c]phenazine), PHEHAT (1,10-phenanthrolino [5,6-b]-1,4,5,8,9,12-hexaazatriphenylene) or TAPHAT (1,4,5,8-tetraazaphenanthrene[9,10-b]-1,4,5,8,9,12-hexaazatriphenylene). 27,[39][40][41][42][43] The structure of these ligands are presented in the ESI.…”

Low-Temperature Observation of the Excited-State Decay of Ruthenium-(Mono-2,2′:6′,2″-Terpyridine) Ions with Innocent Ligands: DFT Modeling of an 3MLCT–3MC Intersystem Crossing Pathway

“…Metal complexes have been extensively studied and have been widely utilized in various aspects of research during the past 50 years. − It can be generalized from these studies that the relative energetics between triplet metal-to-ligand charge transfer emitting states ( 3 MLCT, T e ) and triplet metal-centered excited states ( 3 MC, emission quencher) of ruthenium polypyridine complexes would determine the suitability for a specific photochemical application. , For example, the rate constant for an internal conversion from 3 MLCT to 3 MC, k ic ( 3 MLCT → 3 MC state), for Ru-polypyridine complexes quenches the phosphorescence at room temperature (RT), a characteristic that could be harmful to photodynamic therapy (PDT) but favorable for photochemotherapeutic (PCT) applications. , …”