Nonlinear fluorescence through intermolecular energy transfer and resolution increase in fluorescence microscopy

We investigate a novel concept to efficiently generate multiphoton induced fluorescence from organic molecules. The concept is based on frustrating th e energy transfer between a fluorescent donor and one or more accepters in conjugated molecules. The nonlinearity is not based on higher order molecul ar susceptibilities but entirely on their linear properties. Therefore, in contrast to nonresonant multiphoton absorption, this method does not requir e high local intensities. Likewise, the production of visible fluorescence does not require an infrared excitation wavelength Hence, when applied to s canning microscopy this property is predicted to increase spatial resolutio n. Instead of the similar to 10 GW/cm(2) required in non-resonant multiphot on excitation, focal intensities of similar to 10 MW/cm(2) are expected to produce an equally strong nonlinear signal. The predicted resolution is up to 30% greater than that of an ideal confocal microscope operating at the s ame fluorescence wavelength. The resolution improvement over non-resonant t wo-photon absorption microscopes is about two-fold in all directions.