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SUMMARY:Solar Photoconversion: Proton Reduction Photocatalysis and Sensiti
 zed Triplet Fusion  - Prof. Felix Castellano\, North Carolina State Univer
 sity (USA)
DTSTART:20141212T143000Z
DTEND:20141212T153000Z
UID:TALK56173@talks.cam.ac.uk
CONTACT:Dr. Stavros Athanasopoulos
DESCRIPTION:For the solar-powered water splitting reaction to proceed effi
 ciently\, new classes of light-absorbing sensitizers and hydrogen evolutio
 n catalysts are required. We have developed numerous molecular composition
 s based exclusively on coordination compound sensitizers and catalysts cap
 able of reducing protons to hydrogen in pure water and water-rich solvent 
 mixtures using visible light. In addition to the design\, synthesis\, and 
 characterization of various molecules that serve either as sensitizers or 
 catalysts in these solar energy conversion schemes\, we have developed new
  apparatus’ for parallel high-throughput screening of these photocatalyt
 ic compositions\, monitoring pressure\, GC\, and MS in real-time throughou
 t the time course of the photoreactions. This combinatorial approach to so
 lar fuels photocatalysis has already led to significant understanding and 
 optimization of numerous hydrogen-producing compositions\, permitting us t
 o focus on the best systems for detailed transient absorption and IR mecha
 nistic studies. This presentation will highlight advances incorporating al
 l first-row transition metal complexes\, based on a recently developed cla
 ss of Cu(I) sensitizers exhibiting unprecedented excited state lifetimes w
 orking in concert with Co(III) hydrogen evolution catalysts\, as well as c
 hampion compositions functioning in pure water based on new classes of Ru(
 II) and Ir(III) sensitizers and Co(II) polypyridyl catalysts. Details rela
 ted to the transient spectroscopy of these molecular photocatalytic system
 s will also be presented.\n\nAnother focus of our research program involve
 s the study of sensitized triplet fusion (TF) in solution using highly pho
 tostable metal-organic chromophores in conjunction with energetically appr
 opriate organic molecules with large singlet-triplet gaps. Selective excit
 ation of the long-wavelength absorbing sensitizer efficiently generates lo
 ng-lived triplet states that serve as energy transfer donors. In the prese
 nce of appropriate molecular acceptors\, diffusion controlled triplet-trip
 let energy transfer takes place\, producing the excited triplet state of t
 he acceptor while regenerating the ground state of the sensitizer. When su
 fficient numbers of the sensitized triplets are produced\, TTA takes place
  which results in either frequency upconverted light or the formation of d
 esired chemical products. Various combinations of donor and acceptor have 
 been explored and data will be presented on a number of these systems span
 ning light conversions ranging from the near-visible to the near-IR. This 
 presentation will also describe many examples of upconversion phenomena re
 alized in solid-state polymeric materials along with emerging classes of a
 cceptor/annihilator chromophores. TF processes will be shown to operate at
  high efficiencies with concomitant linear incident power density response
 \, demonstrated in both theory and experiment using non-coherent photons. 
 Finally\, upconversion-based photoaction observed in water splitting photo
 electrochemical cells and operational photovoltaics will be discussed.\n
LOCATION:Kapitza Building Seminar Room\, Cavendish Laboratory\, Department
  of Physics
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