Introduction Decades of effort in structural biology and ultrafast spectroscopy have elucidated many details of natural photosynthesis (Blankenship, 2002; Hu et al., 2002), and it is now a well-established fact that the initial light-harvesting process that leads up to the collection of energy at reaction centres, where charge transfer reaction occurs, is a process with almost perfect efficiency. The mechanism underlying the energy migration in a photosynthetic system is a fundamentally quantum-mechanical one, known as excitation energy transfer (EET) or resonance energy transfer (RET) (Silbey, 1976; Agranovich and Galanin, 1982; Scholes, 2003; May and Kühn, 2011; Olaya-Castro and Scholes, 2011). Resonance energy transfer is ubiquitous, and had been observed as sensitized luminescence long before modern quantum-mechanical understanding of molecular systems was established (Agranovich and Galanin, 1982). Normally, when a molecule becomes excited electronically by absorbing a photon, it luminesces by emitting another photon, within about a nanosecond, if it is fluorescence, or much later for phosphorescence. However, when another molecule with similar excitation energy is present within a distance of tens of nanometres, it can swap its excitation with the molecule as follows: D∗ + A → D + A∗, where D∗ (D) is the excited (ground) state donor of the energy and A (A∗) is the ground (excited) state acceptor. Thus, the excitation of D sensitizes that of A. Clear and sensible understanding of the RET process had been beyond the reach of classical mechanics as had any other molecular processes involving matter–radiation interaction.
All Science Journal Classification (ASJC) codes
- Biochemistry, Genetics and Molecular Biology(all)