Eximer forming state

In addition to parinaroyl phospholipids, pyrene fatty acid derivatives may be used. Such phospholipids have a concentration-dependent emission spectrum (Roseman and Thompson, 1980). At low concentrations of the derivative within the bilayer, the fluorescence is maximal at a wavelength below 400 nm. At higher concentrations of the derivative, the excited state monomers can associate with a ground state monomer to form a dimer complex, or eximer, in a diffusion-controlled process. The maximum emission wavelength of the eximer shifts to approximately 470 nm. The ratio of the eximer to monomer fluorescent intensity is proportional to the concentration of the probe molecules within the bilayer. 

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