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

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 (τT<0.6 μs) than those containing pyrene (τT 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.

A Ru(II) polypyridyl complex bearing aldehyde functions as a versatile synthetic precursor for long-wavelength absorbing photodynamic therapy photosensitizers

“…[9][10][11][12][13][14] As a highly investigated class of compounds, [Ru(phen)3] 2+ derivatives have been studied as PDT PSs. [15][16][17][18] Several examples have shown that the photophysical properties, including absorption, emission as well as excited states lifetimes can be influenced by choice of the coordinated ligands. [5,9,11,13,19] Next to suitable photophysical properties, the biological abilities of a PS including, for example, cellular localisation or mechanism of cellular uptake, play a predominant role in the efficiency of the treatment.…”

Charge separation, charge recombination and intersystem crossing in orthogonal naphthalimide–perylene electron donor/acceptor dyad

“…Since the ISC is an electron spin forbidden process, the traditional triplet photosensitizers are mostly based on heavy atom effect, such as those contain Ir(III), Pt(II), Ru(II) and Os(II) transition metal ions [21][22][23][24][25][26]. However, this type of transitional photosensitizers suffer from some disadvantages, for instance, high cost of preparation, weak absorption of light in the visible region, [27,28] toxicity and short triplet lifetime (heavy atom effect can enhance the T 1 → S 0 relaxation) [29,30]. Thus, it is highly desired to design heavy atom-free triplet PSs.…”

David Brown Award: S. Draper / Wiley–CST Green Chemistry Award: C. Wattanakit / Gottfried‐Wilhelm‐Leibniz‐Preis: W. Wernsdorfer

“…Drapers Forschung über die Synthese neuartiger polyaromatischer und lumineszierender Materialien führte kürzlich zu molekularen Materialien mit hohen Quantenausbeuten für Singulett‐Sauerstoff und Aufwärtskonversion. Sie berichtete in einer Angewandte‐Chemie ‐Zuschrift über Iridium(III)‐Komplexe mit pyrenfunktionalisierten 1,10‐Phenanthrolin‐Liganden als Sensibilisatoren der Triplett‐Triplett‐Annihilierungs‐Aufwärtskonversion, und ein Beitrag ihrer Gruppe über Phenanthrolin‐Ruthenium(II)‐Komplexe als Modellsysteme für Hochleistungs‐Triplettphotosensibilisatoren wurde auf dem Titelbild von ChemPhotoChem vorgestellt.…”