1,10‐Phenanthroline Ruthenium(II) Complexes as Model Systems in the Search for High‐Performing Triplet Photosensitisers: Addressing Ligand versus Metal Effects

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Abstract
A series of RuII complexes containing extended 1,10‐phenanthroline ligands with triphenylamine (TPA) and/or pyrene as light‐harvesting chromophores, were synthesised and investigated in triplet photosensitising applications. “Chemistry‐on‐the‐complex” methods were employed using Sonogashira cross‐coupling reactions. Tunable absorption and triplet lifetimes were achieved depending on the type and number of the chromophores. Intense absorption in the visible region was common to the generated complexes. Those RuII complexes containing only TPA appendages showed much shorter triplet lifetimes (τTτT up to 148 μs). The complexes were explored as triplet photosensitisers for singlet‐oxygen (1O2) photosensitisation and triplet–triplet annihilation based upconversion applications. The best performing complex, Ru‐5, with a single pyrene chromophore, displayed the highest 1O2 quantum yield (ΦΔ=84.4 %) and an attractive upconversion quantum yield (ΦUC=14.7 %). A comparison of the results with those of analogous IrIII complexes comprising the same large N^N coordinating ligands showed that both sets of complexes exhibit the same ligand‐dependent trends in behaviour. The implication is that synthetically accessible RuII complexes might be effective model systems for predicting those ligand frameworks likely to give the highest performing IrIII‐based triplet photosensitisers.
Funding Information
  • Science Foundation Ireland (SFI/15/1A/3046, SFI/IACA/3413, SFI/15/TIDA/2952)

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