Solar Fuels by Means of Photo-induced Electron Transfer in Supramolecular Metal Complexes

Light absorption does not just lead to bond breaking and dissociation. It can also result in light emission and electron transfer; these processes offer many opportunities, especially if linked to the response of a supramolecular system. We have used metalloporphyrins as selective long-wavelength chromophores in supramolecular photochemical experiments, using light absorption to:

  • observe photo-induced charge separation on picosecond1 and nanosecond timescales.
  • cause steady state ligand substitution at a site remote from the position of light absorption (Fig. 1).1,2
  • investigate photocatalytic properties related to sustainable fuels (Fig. 2).

The intimate mechanism of such processes requires spectroscopy on a time-scale as short as picoseconds. We have used IR spectroscopy to define the time sequence of the processes that occur in the metalloporphyrins (Fig. 1) on both picosecond1 and nanosecond timescales. Remarkably, we can detect that photo-induced electron transfer from the metalloporphyrin to the rhenium bipyridine unit has already taken place only 1 ps after the laser shot, forming a charge separated or radical state that in some cases last for several microseconds.

We are working in collaboration with four other research groups in the UK to develop a Solar Nanocell, an artificial device that uses visible-light toward the tandem conversion of CO2 and alkanes to CO and alcohols, respectively (Fig. 2) SolarCAP Consortium for Artificial Photosynthesis. The supramolecular metalloporphyrin–rhenium tricarbonyl bipyridine complexes are currently being studied to photochemically reduce CO2 to CO by selectively light-excitation of the metalloporphyrin core.

Photo-induced electron transfer in a metalloporphyrin appended to a rhenium carbonyl

Design of Solar Nanocell

Selected Publications

  1. Ultrafast Charge Separation In a Photoreactive Rhenium-Appended Porphyrin Assembly Monitored by Picosecond Transient Infrared Spectroscopy, J. Am. Chem. Soc., 2006, 128, 4253–4266.
  2. Remote site photosubstitution in metalloporphyrin–rhenium tricarbonylbipyridine assemblies: photo-reactions of molecules with very short lived excited states, Dalton Trans., 2008, 4259–4269.