Two-dimensional spectroscopy can now be done using visible light. This allows the electronic couplings between energy levels to be measured directly and sheds new light on how molecules function in photosynthesis. How light is converted into chemicalenergy in a photosynthetic system is largely determined by the vibrational and electronic dynamics of the complex biological macromolecules involved. An essential step in the elucidation of these mechanisms is the combined determination of structure anddynamics. The extension of nuclear magnetic resonance (NMR) spectroscopy into multiple dimensions was introduced not long ago as one of the great advances in the study of the structure of proteins in solutions. Now, Fleming and co-workers, writing on page 625 of this issue, have transferred these principles of multidimensional spectroscopy to the electronic spectrum, where the wavelengths are about 10~(-7_ of those in the NMR regime. This has allowed the first direct measurement of electronic couplingscombined with the dynamics of excitations transferring between molecular energy levels in photosynthetic antennas.
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