Tuning the excited state properties of [2.2]paracyclophane-based antennas to ensure efficient sensitization of lanthanide ions or singlet oxygen generation.

Abstract

The multi-step synthesis of original antennas incorporating substituted [2.2]paracyclophane (pCp) moieties in the -conjugated skeleton is described. These antennas, functionalized with electron an donor alkoxy fragment (A 1 ) or with a fused coumarin derivative (A 2 ) are incorporated in a triazacyclonane macrocyclic ligand L 1 or L 2 , respectively for the design of Eu(III), Yb(III) and Gd(III) complexes. A combined photophysical/theoretical study reveals that A 1 presents a charge transfer character via the through-space paracyclophane conjugation, whereas A 2 presents only local excited states centered on the coumarin-paracyclophane moiety, strongly favoring triplet state population via intersystem crossing. The resulting complexes EuL 1 and YbL 2 are fully emissive in the red and near infrared, respectively whereas the GdL 2 complex acts as photosensitizer for the generation of singlet oxygen.