Fluorescence resonance energy transfer in novel multiphoton absorbing dendritic structures

A series of small dendritic structures containing one of two efficient multiphoton absorbing dyes at the periphery and a nile red derivative at the core have been synthesized. These molecules display efficient (>96%) fluorescence resonance energy transfer (FRET) from the periphery to the core on selective excitation of the two-photon absorbing chromophore by either UV (linear absorption) or high-intensity IR (nonlinear absorption) radiation. In addition, a significant increase in core emission is observed on excitation of the peripheral chromophores, compared to direct excitation of the core. This "antenna effect" essentially doubles between increasing dendrimer generations within a series. The combination of the ability of the peripheral chromophores to absorb high-intensity IR radiation, coupled with a very efficient energy transfer process and a significant increase in the fluorescence of the acceptor chromophore, makes these molecules potentially useful for a variety of applications, including optical power limiting and biomedical imaging.