Figure 3.

Orientation of donor and acceptor and its influence on the orientation factor κ 2. κ² depends on the relative arrangements of excited donor's electric field and acceptors absorption dipole. (A) A perpendicular arrangements of the transition dipoles results in κ² = 0 and prevents energy transfer between donor and acceptor. (B) If the dipoles are arranged side-by-side, κ² becomes 1. (C) A head to tail arrangement of the dipoles favors FRET as κ² = 4, the highest value that is possible for κ².