Tris(2,2‘-bipyridine)ruthenium(II) Cations as Photoprobes of Clay Tactoid Architecture within Hectorite and Laponite Films

The adsorption and intercalation of the cationic luminescence probe, tris(2,2‘-bipyridine)ruthenium(II) complex ([Ru(bpy) 3 ] 2+ or Rubpy), into hectorite and Laponite host clay films were investigated. Because the photophysical properties of Rubpy are strongly influenced by the lamellar nanospace of the smectite host, Rubpy serves as a unique photoprobe of host−guest and guest−guest interfaces within inorganic−organic nanocomposites. The stacking patterns of the host tactoids influence guest luminescence through direct mediation of ion clustering and self-quenching phenomena. Spectral red shift of emission wavelengths and decreased lifetimes were observed with increased guest loading. The extent of red shift in the Rubpy/Laponite films indicated a more fluid guest microenvironment. Rubpy/Laponite films exhibit enhanced potential for photonic and sensor applications with increased optical transparency, intense luminescence, and longer luminescence lifetimes. Cointercalation of the cationic surfactant, trimethylcetylammonium cation, promotes two-dimensional tiling of Laponite tactoids and may afford selective tuning of fluorophore packing.