Intermolecular energy transfer across nanocrystalline semiconductor surfaces.
The yields and dynamics for energy transfer from the metal-to-ligand charge-transfer excited states of Ru(deeb)(bpy)(2)(PF(6))(2), Ru(2+), and Os(deeb)(bpy)(2)(PF(6))(2), Os(2+), where deeb is 4,4'-(CH(3)CH(2)CO(2))(2)-2,2'-bipyridine, anchored to mesoporous nanocrystalline (anatase) TiO(2) thin films were quantified. Lateral energy transfer from Ru(2+)* to Os(2+) was observed, and the yields were measured as a function of the relative surface coverage and the external solvent environment (CH(3)CN, THF, CCl(4), and hexanes). Excited-state decay of Ru(2+)*/TiO(2) was well described by a parallel first- and second-order kinetic model, whereas Os(2+)*/TiO(2) decayed with first-order kinetics within experimental error. The first-order component was assigned to the radiative and nonradiative decay pathways (tau = 1 micros for Ru(2+)*/TiO(2) and tau = 50 ns for Os(2+)*/TiO(2)). The second-order component was attributed to intermolecular energy transfer followed by triplet-triplet annihilation. An analytical model was derived that allowed determination of the fraction of excited-states that follow the two pathways. The fraction of Ru(2+)*/TiO(2) that decayed through the second-order pathway increased with surface coverage and excitation intensity. Monte Carlo simulations were performed to estimate the Ru(2+)* --> Ru(2+) intermolecular energy transfer rate constant of (30 ns)(-1).
Departments of Chemistry and Material Science and Engineering, Johns Hopkins University, Baltimore, Maryland 21218, USA.
Gerard T
GT
Higgins
Bryan V
BV
Bergeron
Georg M
GM
Hasselmann
Fereshteh
F
Farzad
Gerald J
GJ
Meyer
D003460:Crystallization; D004735:Energy Transfer; D009010:Monte Carlo Method; D049329:Nanostructures / Q000737:chemistry*; D009942:Organometallic Compounds / Q000737:chemistry*; D009992:Osmium / Q000737:chemistry*; D010084:Oxidation-Reduction; D012428:Ruthenium / Q000737:chemistry*; D012666:Semiconductors; D013499:Surface Properties; D013997:Time Factors
D009942:Organometallic Compounds; D009992:Osmium; D012428:Ruthenium