Stabilizing [Ru(bpy)3]3+ at room-temperature in a hybrid crystal with unusual luminescence and ultralow thermal conductivity

Abstract

Solid-state photophysical properties of [Ru(bpy)3]2+ are well-studied, whereas those of [Ru(bpy)3]3+ remain elusive. Here, we report ambient-conditions stabilization of [Ru(bpy)3]3+ in an organic-inorganic hybrid crystal, [Ru(bpy)3]2Ag6Br12. Utilizing two-dimensional hexagonal anionic network, (Ag6Br11)n5n-, featuring strong argentophilic interactions, this system stabilizes the spin-bearing low-spin d5 Ru(III) exhibiting unusual room-temperature photoluminescence with three emission peaks (~586, ~612, and ~686 nm), a behavior rarely seen in ruthenium tris(bipyridine) systems. Temperature-dependent and time-resolved photoluminescence measurements reveal average lifetimes of ~10 ns at 300 K across all peaks. The origin of the three emission peaks is identified by time-dependent density functional theory calculations, revealing three doublet ligand-to-metal charge-transfer states to a doublet ground state transitions. The extracted spin-density plot suggests near spin-degeneracy of the dz2, dx2-y2 and dxy orbitals, corroborating trigonal antiprismatic (D3d) microsymmetry. The organic-inorganic hybrid also displays ultralow thermal conductivity (~0.21 W·m-1·K-1 at 480 K), qualifying it as a promising multifunctional material.