Förster (Theoretical basis)

Förster resonance energy transfer (FRET) is a process where energy transfers non-radiatively from an excited donor molecule to a nearby acceptor molecule through dipole-dipole interactions. This transfer depends on how close they are (typically 1-10 nanometers), how well the donor's emission spectrum overlaps with the acceptor's absorption spectrum, and their relative orientation. When the donor molecule is excited by light, instead of emitting a photon, it can pass its energy directly to the acceptor, which then may emit light itself. FRET is widely used in studying molecular interactions and distances at the nanometer scale.