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)_n^5n-, 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 d_z², d_x²_-y² and d_xy orbitals, corroborating trigonal antiprismatic (D_3d) 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.