Tuning Excited-State Properties of [2.2]Paracyclophane-Based Antennas to Ensure Efficient Sensitization of Lanthanide Ions or Singlet Oxygen Generation
Shiqi Wu, Laura Abad Galán, Margaux Roux, François Riobé, Boris Le Guennic, Y. Guyot, Tangui Le Bahers, Laurent Micouin, Olivier Maury, Erica Benedetti
Abstract
The multistep synthesis of original antennas incorporating substituted [2.2]paracyclophane (pCp) moieties in the π-conjugated skeleton is described. These antennas, functionalized with an electron donor alkoxy fragment (A1) or with a fused coumarin derivative (A2), are incorporated in a triazacyclonane macrocyclic ligand L1 or L2, respectively, for the design of Eu(III), Yb(III), and Gd(III) complexes. A combined photophysical/theoretical study reveals that A1 presents a charge transfer character via through-space paracyclophane conjugation, whereas A2 presents only local excited states centered on the coumarin–paracyclophane moiety, strongly favoring triplet state population via intersystem crossing. The resulting complexes EuL1 and YbL2 are fully emissive in red and near-infrared, respectively, whereas the GdL2 complex acts as a photosensitizer for the generation of singlet oxygen.