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High Extinction Coefficient Ru‐Sensitizers that Promote Hole Transfer on Nanocrystalline TiO 2
Author(s) -
Abrahamsson Maria,
Hedberg Joachim H. J.,
Becker HansChristian,
Staniszewski Aaron,
Pearson Wayne H.,
Heuer William B.,
Meyer Gerald J.
Publication year - 2014
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201301193
Subject(s) - nanocrystalline material , materials science , extinction (optical mineralogy) , molar absorptivity , nanocrystal , chemical engineering , analytical chemistry (journal) , nanotechnology , chemistry , mineralogy , environmental chemistry , optics , physics , engineering
Two series of Ru II polypyridyl compounds with formulas [(bpy) 2 RuL](PF 6 ) 2 and [(deeb) 2 RuL](PF 6 ) 2 , 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 2 . These compounds possess notably high extinction coefficients (≥40 000 M −1 cm −1 @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 2 thin films, both the free ligands (L) and their corresponding [(deeb) 2 RuL] 2+ complexes exhibited rapid excited‐state electron injection into TiO 2 ; in the case of the complexes, this was followed by rapid ( k >10 8 s −1) hole transfer from Ru III to the 1,3‐dithiole ring of the L ligand. Observation of diffusion‐limited reductive quenching of the [Ru(bpz) 3 ] 2+ * (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 2 ‐anchored complexes.