Chromophores contain conjugated electron systems–alternating single and double bonds that create delocalized π electrons capable of absorbing photons at specific wavelengths.
When a chromophore absorbs a photon, an electron transitions from the ground state (S0) to an excited state (S). The chromophore then returns to ground state through one of several pathways:
* Fluorescence: Photon emission at a longer wavelength (Stokes shift)
* Non-radiative decay: Energy dissipated as heat
* FRET: Energy transferred to nearby acceptor chromophore
The probability of each pathway depends on the chromophore's environment. In FRET, the presence of an acceptor within 1–10 nm provides a highly efficient alternative decay pathway–reducing donor fluorescence lifetimeLoading... and enabling detection of molecular proximity.