A Series of Fluorene-Based Two-Photon Absorbing Molecules: Synthesis, Linear and Nonlinear Characterization, and Bioimaging

The synthesis, structural, and photophysical characterization of a series of new fluorescent donor−acceptor and acceptor−acceptor molecules, based on the fluorenyl ring system, with two-photon absorbing properties is described. These new compounds exhibited large Stokes shifts, high fluorescence quantum yields, and significantly, high two-photon absorption cross sections, making them well suited for two-photon fluorescence microscopy imaging. Confocal and two-photon fluorescence microscopy imaging of COS-7 and HCT 116 cells incubated with probe I showed endosomal selectivity, demonstrating the potential of this class of fluorescent probes in multiphoton fluorescence microscopy.