Flourescence and self-absorption cause shift in wavelength

[fog37]

Hello Forum,

I understand how fluorescence works: there is an absorption spectrum and an emission spectrum. The two spectra are shifted relative to each other in the sense that the absorption peak wavelength is different from the emission peak wavelength (Stokes shift).
That said, fluorescent dyes may also fluoresce differently at high concentrations (self-quenching).

Self-quenching reduce the intensity of the fluorescent emission but can also leads to a shift of the peak fluorescence wavelength. Why? Why would the higher concentration and self-absorption between the clorophores cause a shift in the emission wavelength? A molecule absorbs the fluorescent light emitted by the other...Thanks,
Fog37

 

[Ygggdrasil]

Self-quenching, in general, is not due to one fluorophore absorbing the emitted light of a neighboring fluorophore. In many cases, self-quencing occurs due to excimer or exiplex formation – fluorophors physically interacting to form complexes that can change their electronic properties (for example, providing new non-radiative pathways for relaxation, explaining the lowered quantum yield, and altering the energy levels of the molecules, explaining the shifted emission spectrum).