Dueling dipoles: In search of a new theory of photosynthetic energy transfer

Dueling dipoles: In search of a new theory of photosynthetic energy transfer: The first step in designing such a complex involved the use of Förster theory to calculate the efficiency of energy transfer between dyes. This theory posits that intermolecular energy transfer occurs when oscillating dipoles – chemical compounds that carry spatially separated and opposite electric charges – cause adjacent dipoles to oscillate in their turn. Dipole orientation plays a crucial role in the process. Orthogonally oriented dipoles are assumed to be incapable of energy transfer. If molecules are oriented in parallel, energy transfer is allowed.

To everyone's surprise, the measurements actually showed that energy can be transferred between orthogonally arranged chromophores with almost 100% efficiency. As Langhals emphasizes: "The process is extraordinarily efficient. This is reflected in the extremely short reaction time – 9.4 billionths of a second. The findings rule out the idea that energy transfer occurs by a dipole-based mechanism. Instead, our results imply a low-frequency mode of coupling via intramolecular vibrations."