Expanding the Family of Fluorescent Coumarin[4]arenes: Improved Synthesis, π-Extension, and Characterization

A novel series of bicyclic fluorescent heterocalixarenes – C-alkyl coumarin[4]arenes – with built-in chirality has been synthesized successfully in excellent yields under well-optimized, improved reaction conditions. Further, structural elaboration (including π-extension) of coumarin[4]arenes has been demonstrated by using Pd-catalyzed Suzuki and Sonogashira cross-coupling methods. All of these macrocycles are shown to possess averaged C4-symmetric conformation in solution as opposed to the coumarin[4]arene tetratriflate derivative of C2 symmetry in the solid state. Finally, the macrocyclic coumarin[4]arenes reveal UV/near-UV absorption and visible blue emission in solution. Such a visible blue luminescence of this macrocycle highlights its potential for sensing, bioimaging, and light-emissive applications.