Aggregation of phosphorescent Pd(II) and Pt(II) complexes with lipophilic counter-anions in non-polar solvents

Phosphorescent cationic tridentate C^N^N (HC^N^N = 6-(2-R₂,4-R₁-phenyl)-2,2'-bipyridine; R₁ = R₂ = H or F, or R₁ = OMe, R₂ = H) cyclometallated Pd(II) complexes with an N,N-dimethyl-imidazol-allenylidene ancillary ligand (L) and their corresponding Pt(II) congeners have been synthesized and characterized, following the previously reported preparation of the complex [Pd(6-phenyl-2,2'-bipyridine)L]⁺. For these cationic Pd(II)/Pt(II) complexes with 2,3,4-tris(dodecyloxy)benzenesulfonate (LA^-) counter-anions in mixed CH₂Cl₂/toluene solvents, uniform square flake or fibre-like aggregates were formed. Corresponding multicolour phosphorescence with obvious metal-metal-to-ligand charge transfer (MMLCT) features gradually changed from red to NIR by manipulating the various fractions of Pd/Pt species. Circular dichroism (CD) and circularly polarized luminescence (CPL) derived from the fibre-like Pd aggregates of [Pd(6-(2,4-difluorophenyl)-2,2'-bipyridine)L]⁺ in chiroptical CH₂Cl₂/limonene solvents were achieved with an isodesmic aggregation mode. Dispersive metallophilic interactions are claimed to be the driving force for these photo-functional aggregates.