Water-soluble two-photon fluorophores based on paracyclophane

We report the synthesis, linear and nonlinear spectroscopy of the paracyclophane-based two-photon absorption (TPA) fluorophores. Two-photon induced fluorescence (TPIF) measurements in water show a substantial decrease in TPA cross section (delta) and fluorescence quantum yield (eta), relative to toluene. We note that to obtain optimum two-photon action cross sections (eta delta) in water, one needs to fine tune the intramolecular charge transfer (ICT). Microenvironment modulation using the micellar structure in water increases eta delta values similar to those obtained in toluene. The measured eta delta values in water are the highest among reported so far, suggesting important guidelines for designing of optimized TPIF molecular-labels.