Photoinitiated multi-step charge separation and ultrafast charge transfer induced dissociation in a pyridyl-linked photosensitizer-cobaloxime assembly

Brad S. Veldkamp, Won Sik Han, Scott M. Dyar, Samuel W. Eaton, Mark A Ratner, Michael R Wasielewski

Research output: Contribution to journalArticle

52 Citations (Scopus)

Abstract

Using visible and near-infrared transient absorption spectroscopy to track distinct excited state, cation, and anion signals, we report a detailed kinetic analysis of photoinitiated multi-step charge separation and ultrafast charge transfer induced dissociation in a self-assembled donor-bridge-acceptor- cobaloxime triad. The donor-bridge-acceptor ligand consists of a perylene chromophore linked via a xylene bridge to a pyridyl-substituted 1,8-naphthalimide electron acceptor. Coordination of the ligand to the catalyst [Co(dmgBF2)2(L)2], where dmgBF2 = (difluoroboryl)dimethylglyoximato and L = water or a solvent molecule, yields a donor-bridge-acceptor-catalyst triad assembly. Photoexcitation with 416 nm laser pulses generates the perylene S1 excited state. Subsequent electron transfer from perylene to the acceptor occurs in τ = 9.0 ± 0.1 ps followed by electron transfer to the catalyst in τ = 6 ± 1 ps. Of the charge-separated state population formed, 79 ± 1% undergoes charge recombination to either the singlet ground state (τ = 0.8 ± 0.1 ns) or the perylene triplet state (τ = 4.3 ± 0.1 ns). Co(i)-pyridyl bond dissociation with τ = 2.4 ± 0.2 ns competes with intramolecular charge recombination resulting in a 21 ± 1% yield of dissociated oxidized photosensitizer and reduced catalyst. Subsequent diffusional charge recombination occurs with k = (1.8 ± 0.2) × 1010 M -1 s-1. This detailed analysis of the electron transfer and dissociation dynamics of an integrated photosensitizer-catalyst system will inform the rational design of novel molecular assemblies that efficiently absorb photons, transfer electrons, and catalyze fuel-forming reactions.

Original languageEnglish
Pages (from-to)1917-1928
Number of pages12
JournalEnergy and Environmental Science
Volume6
Issue number6
DOIs
Publication statusPublished - Jun 2013

Fingerprint

Perylene
Photosensitizing Agents
Photosensitizers
Charge transfer
catalyst
electron
Catalysts
Electrons
recombination
Excited states
ligand
Naphthalimides
Ligands
Xylenes
Photoexcitation
xylene
atomic absorption spectroscopy
Xylene
Chromophores
Absorption spectroscopy

ASJC Scopus subject areas

  • Renewable Energy, Sustainability and the Environment
  • Environmental Chemistry
  • Pollution
  • Nuclear Energy and Engineering

Cite this

Photoinitiated multi-step charge separation and ultrafast charge transfer induced dissociation in a pyridyl-linked photosensitizer-cobaloxime assembly. / Veldkamp, Brad S.; Han, Won Sik; Dyar, Scott M.; Eaton, Samuel W.; Ratner, Mark A; Wasielewski, Michael R.

In: Energy and Environmental Science, Vol. 6, No. 6, 06.2013, p. 1917-1928.

Research output: Contribution to journalArticle

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