Interfacial Electron Transfer Dynamics of Two Newly Synthesized Catecholate Bound RuII Polypyridyl-Based Sensitizers on TiO2 Nanoparticle Surface – A Femtosecond Pump Probe Spectroscopic Study
✍ Scribed by Tanmay Banerjee; Sachin Rawalekar; Amitava Das; Hirendra N. Ghosh
- Publisher
- John Wiley and Sons
- Year
- 2011
- Tongue
- English
- Weight
- 815 KB
- Volume
- 2011
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Two new catecholate‐bound Ru^II^–polypyridine based sensitizers, (2,2′‐bipyridine){ethyl 3‐(4‐hydroxyphenyl)‐2‐[(4′‐methyl‐2,2′‐bipyridinyl‐4‐carbonyl)amino]propionate}{4‐[2‐(4′‐methyl‐2,2′‐bipyridinyl‐4‐yl)vinyl]benzene‐1,2‐diol)}ruthenium(II) hexafluorophosphate (5) and [(2,2′‐bipyridine)‐(4‐2,2′‐bipyridinyl‐4‐yl‐phenol)‐(4‐{2‐(4′‐methyl‐2,2′‐bipyridinyl‐4‐yl)vinyl}benzene‐1,2‐diol)]ruthenium(II) hexafluorophosphate (6) with secondary electron‐donating groups (tyrosine and phenol, respectively) were synthesized and characterized. Steady‐state optical absorption and emission studies confirm strong coupling between the sensitizers and TiO~2~ nanoparticles. Femtosecond visible transient absorption spectroscopy has been employed to study interfacial electron transfer (IET) dynamics in the dye–nanoparticle systems to explore the influence of the secondary electron‐donating groups on IET dynamics. Electron injection into the conduction band of nanoparticulate TiO~2~ has been confirmed by detection of the conduction band electrons in TiO~2~ ([e^–^]~TiO2~^CB^) and radical cation of the adsorbed dye (D^·+^) in real time monitored by transient absorption spectroscopy. A single exponential and pulse‐width limited (< 100 fs) electron injection has been observed. Back electron transfer (BET) dynamics have been studied by monitoring the decay kinetics of the injected electron in the conduction band of TiO~2~ and by the recovery of the ground state bleach. BET dynamics in dye–TiO~2~ systems for complexes 5 and 6 have been compared with those of [bis(2,2′‐bpy)‐(4‐{2‐(4′‐methyl‐2,2′‐bipyridinyl‐4‐yl)vinyl}benzene‐1,2‐diol)]ruthenium(II) hexafluorophosphate (7), which does not have a secondary electron‐donating group.