Two RuII Linkage Isomers with Distinctly Different Charge Transfer Photophysics

The ligand PHEHAT (PHEHAT = 1,10-phenanthrolino[5,6-b]1,4,5,8,9,12-hexaazatriphenylene) 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+), [RuII(phen)(2)PHEHAT](2+) exhibits an unusual behavior. It appears that this complex has two (MLCT)-M-3 bright states, the lower one being weakly emissive or nonemissive 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 density functional theory 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 behavior of these complexes.

Automated summary

The ligand PHEHAT presents structural asymmetry that affects the photophysical properties of metal ion chelation, leading to different behaviors in [Ru-II(phen)2)HATPHE](2+) and [Ru-II(phen)(2)PHEHAT](2+). The latter exhibits two bright states, with the lower state being weakly or non-emissive depending on solvent and temperature. Experimental and theoretical analysis is crucial to fully understand this intriguing photophysical behavior.