Resonance energy transfer in a novel two-component system: two-photon fluorophore and a photo-chromic acceptor molecule

Two-Photon (TP) excitation followed by Resonance Energy Transfer (RET) is a potentially useful mechanism for multiphoton microscopy in biological research, multi-photon three-dimensional micro-fabrication and it can also give rise to enhanced nonlinear absorption. In this work we use a TP fluorophore as a donor (D) and a photo-chromic (PC) molecule as an acceptor (A). The molecules were chosen so as to display efficient RET to the photo-chromic acceptor following two-photon excitation of the donor. The spectroscopic behavior of each molecule was studied separately and in Mixtures. The RET process following the TP excitation from the TP fluorophore to the photo-chromic molecule was studied using short pulse (2 ps) laser excitation at the TP peak absorption. The fluorescence decay indicates a modified Forster type energy transfer. The system should exhibit enhanced nonlinear absorption beyond the square law of TP absorption as expected in presence of donor itself.