High Extinction Coefficient Ru‐Sensitizers that Promote Hole Transfer on Nanocrystalline TiO2. Issue 6 (19th March 2014)

• Record Type: Journal Article
• Authors: Abrahamsson, Maria; Hedberg, Joachim H. J.; Becker, Hans‐Christian; Staniszewski, Aaron; Pearson, Wayne H.; Heuer, William B.; Meyer, Gerald J.
• Is Part Of: Chemphyschem. Volume 15:Issue 6(2014)
• Page Start: 1154
• Page End: 1163
• Publication Date: 2014-03-19
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.05
• DOI: 10.1002/cphc.201301193
• Languages: English
• ISSNs: 1439-4235

Abstract

<abstract abstract-type="main" xml:lang="en"> <title>Abstract</title> <p>Two series of Ru<sup>II</sup> polypyridyl compounds with formulas [(bpy)<sub>2</sub>RuL](PF<sub>6</sub>)<sub>2</sub> and [(deeb)<sub>2</sub>RuL](PF<sub>6</sub>)<sub>2</sub>, where bpy is 2, 2′‐bipyridine, deeb is 4, 4′‐diethylester‐2, 2′‐bpy, and L is one of several substituted 9′‐(1, 3‐dithiole‐2‐ylidene)‐4′, 5′‐diazafluorene ligands, were studied as potential photosensitizers for TiO<sub>2</sub>. These compounds possess notably high extinction coefficients (≥40 000 <sc>M</sc><sup>−1</sup> cm<sup>−1</sup> @470 nm) which are shown by time‐dependent density functional theory (TD‐DFT) calculations to result from overlapping metal‐to‐ligand charge transfer (MLCT) and ligand‐localized transitions. Low‐temperature absorption and photoluminescence measurements were suggestive of a short‐lived MLCT excited state. When adsorbed onto TiO<sub>2</sub> thin films, both the free ligands (L) and their corresponding [(deeb)<sub>2</sub>RuL]<sup>2+</sup> complexes exhibited rapid excited‐state electron injection into TiO<sub>2</sub>; in the case of the complexes, this was followed by rapid (<italic>k</italic>>10<sup>8</sup> s<sup>−1)</sup> hole transfer from Ru<sup>III</sup> to the 1, 3‐dithiole ring of the L ligand. Observation of diffusion‐limited reductive quenching of the [Ru(bpz)<sub>3</sub>]<sup>2+</sup>* (bpz is 2, 2′‐bipyrazine) excited state by the L ligands in solution supported the occurrence of intramolecular hole transfer following electron injection by the TiO<sub>2</sub>‐anchored complexes.</p> </abstract>