Aggregation-induced emission of cyclometalated rhodium(III) and iridium(III) phenylpyridine complexes with ancillary 1,3-diketones

A joint structural and spectroscopic study of simple bis-cyclometataled rhodium(III) and iridium(III) complexes with 2-phenylpyridine and aromatic beta-diketones (dibenzoylmethane, benzoylacetone, benzoyltrifluoroacetone, and 2-thenoyltrifluoroacetone) reveals an interplay between the solid-state emission efficiency and crystal packing peculiarities of the complexes. Although the prepared rhodium(iii) cyclometalates are isostructural with iridium(iii) analogues, different types of pi-pi interactions are responsible for the aggregation-induced emission (AIE) of the complexes depending on the metal ion. For iridium(iii) complexes, pyridyl-pyridyl contacts are essential for AIE because they lower the energy of the emissive metal-to-ligand charge transfer state below that of the non-emissive state located at the ancillary ligand. Enabled by phenyl-pyridyl interactions partially blocking the population of non-emissive d-d states, solid-state phosphorescence enhancement is successfully achieved in a rhodium(III) complex with ancillary benzoyltrifluoroacetone, which is the first example of a rhodium complex exhibiting AIE.

Automated summary

A joint study of rhodium(III) and iridium(III) complexes with different ligands reveals the relationship between their solid-state emission efficiency and crystal packing. Different types of interactions are responsible for the aggregation-induced emission (AIE) depending on the metal ion. For iridium(III) complexes, pyridyl-pyridyl contacts are essential for AIE, while in a rhodium(III) complex, phenyl-pyridyl interactions enhance solid-state phosphorescence.