Synthesis and Photophysical Properties of New Conjugated Fluorophores Designed for Two-Photon-Excited Fluorescence

Novel elongated push-push fluorophores (e.g., 9) were synthesized by 2-fold Sonogashira or Wittig−Horner reactions. Modulation of the length and topology of the conjugated connectors allows tuning of their photophysical properties. In addition, their photoluminescence can be adjusted by playing on polarity. Derivatives combining enhanced two-photon absorption cross section (σ2) in the visible red and high fluorescence quantum yield (Φ) have been obtained. Such fluorophores hold promise for nonlinear imaging of biological systems.