Ring-Size Control and Guest-Induced Circularly Polarized Luminescence in Heteroleptic Pd₃A₃B₃ and Pd₄A₄B₄ Assemblies

Two new structural motifs within the class of heteroleptic Pd_nA_nB_n assemblies, namely syn-cis-Pd₃A₃B₃ bowls and bowl- (syn) or saddle- (anti) shaped cis-Pd₄A₄B₄ rings are introduced. All of the ten examples share a common longer fluorenone-based bis-monodentate ligand, equipped with meta-pyridine donor groups. The ring size (3- vs. 4-membered) and conformational preference (bowl vs. saddle) are controlled by the choice of the shorter ligand. These carry para-pyridine donors, different aromatic backbones (benzene, thiophene or selenophene) and either no or small or bulky endohedral substituents, serving to control the nuclearity of the heteroleptic rings through different effects (ligand angle, charge distribution or backbone bulk). Moreover, the luminescence of the fluorenone ligand is conserved in the formed architectures. Emission intensity as well as host-guest properties vary depending on the inward-pointing functions. All Pd₃A₃B₃ assemblies are shown to bind chiral guest BINOL bis-sulfonate which imparts its chirality to the entire host-guest complex. This results in a guest-induced circular dichroism (CD) and circularly polarized luminescence (CPL) with dissymmetry factor g_lum up to 10^-3.