Tuning Excited-State Properties of [2.2]Paracyclophane-Based Antennas to Ensure Efficient Sensitization of Lanthanide Ions or Singlet Oxygen Generation

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.