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Title: Disentangling the Physical Processes Responsible for the Kinetic Complexity in Interfacial Electron Transfer of Excited Ru(II) Polypyridyl Dyes on TiO2

Journal Article · · Journal of the American Chemical Society
DOI:https://doi.org/10.1021/jacs.5b12996· OSTI ID:1387631
 [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1];  [1]
  1. Univ. of North Carolina, Chapel Hill, NC (United States)
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Interfacial electron transfer at titanium dioxide (TiO2) is investigated herein for a series of surface bound ruthenium-polypyridyl dyes whose metal-to-ligand charge-transfer state (MLCT) energetics are tuned through chemical modification. The 12 complexes are of the form RuII(bpy-A)(L)22+, where bpy-A is a bipyridine ligand functionalized with phosphonate groups for surface attachment to TiO2. Functionalization of ancillary bipyridine ligands (L) enables the potential of the excited state RuIII/* couple, E+/*, in 0.1 M perchloric acid (HClO4(aq)) to be tuned from –0.69 to –1.03 V vs NHE. Each dye is excited by a 200 fs pulse of light in the visible region of the spectrum and probed with a time-delayed supercontiuum pulse (350–800 nm). Decay of the MLCT excited-state absorption at 376 nm is observed without loss of the ground-state bleach, which is a clear signature of electron injection and formation of the oxidized dye. The dye-dependent decays are biphasic with time constants in the 3–30 and 30–500 ps range. The slower injection rate constant for each dye is exponentially distributed relative to E+/*. The correlation between the exponentially diminishing density of TiO2 sub-band acceptor levels and injection rate is well described using Marcus–Gerischer theory, with the slower decay components being assigned to injection from the thermally equilibrated state and the faster components corresponding to injection from higher energy states within the 3MLCT manifold. These results and detailed analyses incorporating molecular photophysics and semiconductor density of states measurements indicate that the multiexponential behavior that is often observed in interfacial injection studies is not due to sample heterogeneity. Rather, this work shows that the kinetic heterogeneity results from competition between excited-state relaxation and injection as the photoexcited dye relaxes through the 3MLCT manifold to the thermally equilibrated state, underscoring the potential for a simple kinetic model to reproduce the complex kinetic behavior often observed at the interface of mesoporous metal oxide materials.

Research Organization:
Energy Frontier Research Centers (EFRC) (United States). Center for Solar Fuels (UNC EFRC)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
SC0001011; AC05-06OR23100
OSTI ID:
1387631
Journal Information:
Journal of the American Chemical Society, Vol. 138, Issue 13; Related Information: UNC partners with University of North Carolina (lead); Duke University; University of Florida; Georgia Institute of Technology; University; North Carolina Central University; Research Triangle Institute; ISSN 0002-7863
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 73 works
Citation information provided by
Web of Science

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Cited By (9)

Exploration on Charge Transfer and Absorption Spectra of Spiro[fluorene-9,90-xanthene]-based Polyoxometalate Hybrids Toward High Performance Dye-sensitized Solar Cell journal September 2018
Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics journal January 2018
Factors influencing the photoelectrochemical device performance sensitized by ruthenium polypyridyl dyes journal January 2019
Enhancement in Dye‐Sensitized Solar Cells Using Surface Plasmon Resonance Effects from Colloidal Core‐Shell Au@SiO2 Nanoparticles journal May 2019
Mono(2,2′-bipyridyl)Ru II Complex with Four Dimethyl Sulfoxide Ligands as Precursor for cis -Bis-heteroleptic Ru II Complex: Syntheses, Structures, and Substitution Reactions: Mono(2,2′-bipyridyl)RuII Complex with Four Dimethyl Sulfoxide Ligands as Precursor for cis-Bis-heteroleptic RuII Complex: Syntheses, Structures, and S journal October 2018
Stabilized photoanodes for water oxidation by integration of organic dyes, water oxidation catalysts, and electron-transfer mediators journal August 2018
Structural Engineering of Semiconductor Nanoparticles by Conjugated Interfacial Bonds journal April 2019
Impact of Photosensitizing Multilayered Structure on Ruthenium(II)-Dye-Sensitized TiO2-Nanoparticle Photocatalysts journal July 2017
Trapping intermediate MLCT states in low-symmetry {Ru(bpy)} complexes journal January 2017

Figures / Tables (14)

Figure 1(p. 5)figure Figure 1
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Figure 5(p. 14)figure Figure 5
Table 2(p. 17)table Table 2
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Scheme 1(p. 25)figure Scheme 1
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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
catalysis (homogeneous)
catalysis (heterogeneous)
solar (photovoltaic)
solar (fuels)
photosynthesis (natural and artificial)
hydrogen and fuel cells
electrodes - solar
charge transport
materials and chemistry by design
synthesis (novel materials)
synthesis (self-assembly)
dyes and pigments
oxides
metal to ligand charge transfer
ligands
kinetics