Cyanido-bridged diplatinum(ii) complexes: ligand and solvent effect on aggregation and luminescence

Abstract

The association of platinum(II)-based luminophores, which is caused by metal⋯metal and π–π stacking interactions, has been actively exploited in supramolecular construction of photofunctional molecular materials. Herein, we describe a series of bimetallic complexes [{Pt(C^N^^/*N)}₂(CN)][BAr₄^F], containing cyanido-bridged cyclometalated Pt(II) chromophore fragments (HC^N^N = 6-phenyl-2,2′-bipyridine, (benzyltriazolyl)-phenylpyridine, and pyrazolyl-phenylpyridine; HC^N*N = N-pentyl-6-phenyl-N-(pyridin-2-yl)pyridin-2-amine; ^/* denote five/six-membered metallocycles). These compounds are intensely phosphorescent at room temperature showing quantum yields up to 0.73 in solution and 0.62 in the solid state, which are generally higher than those of the mononuclear relatives [Pt(C^N^^/*N)(CN)]. The complex cations bearing sterically unhindered ⁻C^N^N ligands readily assemble in solution, reaching the tetrameric species [{Pt(C^N^N)}₂(CN)]₄⁴⁺ as suggested by diffusion NMR spectroscopy. The size of the aggregates can be regulated by the concentration, temperature, and polarity of the solvent that allows to alter the emission from green to near-IR. In the solid state, the maximum of low-energy luminescence is shifted up to 912 nm. The results show that photophysical properties of discrete complexes and the intermolecular aggregation can be substantially enhanced by utilizing the rigid bimetallic units giving rise to novel dynamic light emitting Pt(II) systems.