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Title: Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics

Abstract

Two sensitizers, [Ru(bpy) 2 (dcb)] 2+ ( RuC ) and [Ru(bpy) 2 (dpb)] 2+ ( RuP ), were anchored to mesoporous TiO 2 thin films and utilized to sensitize the reaction of TiO 2 electrons with oxidized triphenylamines to visible light in CH 3 CN electrolytes.

Authors:
ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]
  1. Department of Chemistry, University of North Carolina at Chapel Hill, Chapel Hill, USA
Publication Date:
Sponsoring Org.:
USDOE
OSTI Identifier:
1411100
Grant/Contract Number:
SC0013461
Resource Type:
Journal Article: Published Article
Journal Name:
Chemical Science
Additional Journal Information:
Journal Volume: 9; Journal Issue: 4; Related Information: CHORUS Timestamp: 2018-01-24 09:44:59; Journal ID: ISSN 2041-6520
Publisher:
Royal Society of Chemistry (RSC)
Country of Publication:
United Kingdom
Language:
English

Citation Formats

DiMarco, Brian N., Troian-Gautier, Ludovic, Sampaio, Renato N., and Meyer, Gerald J. Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics. United Kingdom: N. p., 2018. Web. doi:10.1039/C7SC03839A.
DiMarco, Brian N., Troian-Gautier, Ludovic, Sampaio, Renato N., & Meyer, Gerald J. Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics. United Kingdom. doi:10.1039/C7SC03839A.
DiMarco, Brian N., Troian-Gautier, Ludovic, Sampaio, Renato N., and Meyer, Gerald J. 2018. "Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics". United Kingdom. doi:10.1039/C7SC03839A.
@article{osti_1411100,
title = {Dye-sensitized electron transfer from TiO 2 to oxidized triphenylamines that follows first-order kinetics},
author = {DiMarco, Brian N. and Troian-Gautier, Ludovic and Sampaio, Renato N. and Meyer, Gerald J.},
abstractNote = {Two sensitizers, [Ru(bpy) 2 (dcb)] 2+ ( RuC ) and [Ru(bpy) 2 (dpb)] 2+ ( RuP ), were anchored to mesoporous TiO 2 thin films and utilized to sensitize the reaction of TiO 2 electrons with oxidized triphenylamines to visible light in CH 3 CN electrolytes.},
doi = {10.1039/C7SC03839A},
journal = {Chemical Science},
number = 4,
volume = 9,
place = {United Kingdom},
year = 2018,
month = 1
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1039/C7SC03839A

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  • Laser flash photolysis (337.1 nm) combined with kinetic absorption-emission spectrophotometry has been used to study the photoreduction of tris(2,2'-bipyridine)ruthenium(II) by phenols and the effects of solvent, temperature, and ionic strength on electron transfer kinetics and yields. The excited-state quenching rate constants (k/sub q/) are in the range 1 x 10/sup 6/-5 x 10/sup 9/ M/sup -1/s/sup -1/ for substituted phenolate ions (pH 12.7) and correlate well with Hammett sigma/sup +/ values and with oxidation potentials. The plot of RT in k'/sub q/ against E/sub ArO./ArO/sup -// has a slope of -0.56, k'/sub q/ being the quenching rate constant corrected formore » the initial diffusional process. Arrhenius plots for k/sub q/ in the cases of p-CH/sub 3/O-C/sub 6/H/sub 4/O/sup -/, C/sub 6/H/sub 5/O/sup -/, and p-COO/sup -/-C/sub 6/H/sub 4/O/sup -/ as quenchers in aqueous solutions are linear from 0 to 80/sup 0/C. With p-methoxyphenolate ion and p-methoxy-N,N-dimethylaniline as quenchers, k/sub q/ increases on changing solvent from water to 95% ethanol or 95% acetone; k/sub q/ goes through a minimum at intermediate solvent compositions. Electron transfer yields (eta) are 0.3 to 1.0 for various phenolate ions in aqueous solutions (pH 12.7). For p-methoxyphenolate ion and p-methoxy-N,N-dimethylaniline, eta exhibits an increasing trend at elevated temperatures, in aqueous solvent systems richer in the nonaqueous component (acetone or ethanol), and at lower ionic strengths. The excited-state absorption spectrum (triplet-triplet) or tris(2,2'-bipyridine)ruthenium(II) in aqueous solution (230 to 800 nm) shows small absorption at (500 to 800 nm) and prominent three-band feature at 240 to 400 nm.« less
  • The temperature and free energy dependence of electron transfer from the primary semiquinone (Q/sub A/sup .-/) to the oxidized bacteriochlorophyll dimer ((BChl)/sub 2//sup .+/ have been measured in the reaction center protein from Rhodopseudomonas sphaeroides in which the native Q/sub A/, ubiquinone-10, has been removed and replaced by one of 11 substituted 9,10-anthraquinones, seven 1,4-naphthoquinones, 1,2-naphthoquinone, or five 1,4-benzoquinones. For 19 of these quinones an in situ midpoint potential value at 295 K for the Q/sub A//Q/sub A//sup .-/ couple was available providing a series of reaction center proteins with a variation of reaction -..delta..G/sup 0/ from 0.49 to 0.81more » eV. The E/sub 1/2/ values for the remaining Q/sub As/ were estimated from measurements on quinones in solution, extending the reaction -..delta..G/sup 0/ range from 0.11 to 0.94 eV. The rates of intraprotein electron transfer from the various Q/sub A//sup .-/ molecules to (BChl)/sub 2//sup .+/ were found to be virtually independent of temperature from 5 to 100 K and, where measured, to decrease severalfold from 100 to 300k, a pattern well-known for native reaction center protein. Preliminary attempts have been made to model the observed dependence of the electron-transfer rate on the -..delta..G/sup 0/ and temperature in terms of current theories that describe electron-transfer reactions as nonadiabatic, multiphonon, nonradiative decay processes.« less
  • We have thoroughly investigated electron capture from a hydrogen atom by bare nuclei at intermediate and high energies. The first Born approximation with and without correct boundary conditions is used to compute total cross sections. Both methods possess the same perturbation potential for the reaction under study. The only difference is in the logarithmic phase distortion of the exit channel state due to the long-range Coulomb interaction between the two aggregates. Evidence is presented which substantiates that these Coulomb phases for the relative motion of heavy particles are of paramount importance for an adequate description of charge exchange. The standardmore » Jackson-Schiff approximation which does not consider the boundary condition problem fails completely in comparison with the measurement. In contrast, the first Born approximation with the correct boundary conditions, which takes the asymptotic Coulomb effect into full account, is found to be systematically in excellent agreement with the experimental data for values of the projectile charge ranging from 1 to 6.« less
  • Nanosecond laser flash photolysis and photocurrent measurements have been used to investigate use of [Ru(bpy) 2((4,4'-PO 3H 2) 2bpy)] 2+ attached to TiO 2 nanoparticle films, TiO 2-Ru II, in a dye-sensitized photoelectrosynthesis cell (DSPEC) configuration for H 2 production. In these experiments, laser flash excitation of TiO 2-Ru II and rapid injection lead to TiO 2(e -)-Ru III with subsequent TiO 2(e -)-Ru III → TiO 2-Ru II back electron transfer monitored on the nsec time scale with and without added triethanolamine (TEOA) and deprotonated ethylenediaminetetraacetic tetra-anion (EDTA 4-) as irreversible electron transfer donors. With added TEOA or EDTAmore » 4-, a competition exists between back electron transfer and scavenger oxidation with the latter leading to H 2 production in the photoelectrosynthesis cell. Reduction of TiO 2(e -)-Ru III by both TEOA and EDTA 4- occurs with k D ~ 10 6 M -1 s -1. EDTA 4- is a more efficient scavenger by a factor of ~3 because of a more favorable partition equilibrium between the film and the external solution. Its increased scavenger efficiency appears in incident photon-to-current conversion efficiency (IPCE) measurements, in electron collection efficiencies (η coll), and in photocurrent measurements with H 2 production. Evaluation of electron collection efficiencies by transient current measurements gave η coll ~ 24% for TEOA and ~ 70% for EDTA 4-. The dynamics of back electron transfer are minimized, and collection efficiencies, photocurrents, and hydrogen production are maximized by application of a positive applied bias consistent with the results of I-V measurements. A pH dependent plateau is reached at ~0 V at pH = 4.5 (EDTA 4-) and at ~ -0.4 V at pH 6.7 (TEOA). The difference is qualitatively consistent with the influence of pH on electron population in trap states below the conduction band and the role they play in back electron transfer. The excitation dependence of IPCE measurements matches the spectrum of TiO 2-Ru II with IPCE values ~3 times higher for EDTA 4- than for TEOA as noted above. Absorbed photon-to-current efficiency (APCE) values are light-intensity dependent because of the effect of multiple injection events and the influence of increasing trap site electron densities on back electron transfer. The key to efficient H 2 production is minimizing back electron transfer. Application of a sufficiently positive potential relative to E CB for TiO 2 accelerates loss of electrons from the film in competition with back electron transfer allowing for H 2 production with efficiencies approaching 14.7% under steady-state irradiation.« less