Energy transfer in supramolecular [Crypt-RE]-[W6I14] solids

Abstract

Photophysical properties of tungsten iodides with the [W₆I₁₄]²⁻ cluster core have been described with respect to phosphorescence and phosphorescence quenching by molecular oxygen. This process involves energy transfer from excited triplet states of the cluster onto molecular oxygen. In the present study we investigate deactivation channels of exited triplet states of the [W₆I₁₄]²⁻ cluster towards rare earth ions. For this purpose, we synthesized several supramolecular assemblies made of [W₆I₁₄]²⁻ clusters and metal cryptates and investigated their crystal structures and photophysical properties. UV/Vis photoexcitation of solid [Crypt-A]-[W₆I₁₄] (A = alkaline metal) and [Crypt-RE]-[W₆I₁₄] revealed phosphorescence of the cluster, respectively of the photophysically active rare earth metal (RE) center. A cluster to cryptate energy transfer is proven with a photophysically active rare earth ion by the emission of Yb³⁺ at 977 nm (²F_5/2–²F_7/2) and Nd³⁺ 1072 nm (⁴F_3/2–⁴I_11/2). These results show that an effective excitation of near-infrared-emitting rare earth ions is possible under excitation up to 550 nm with [Crypt-RE]-[W₆I₁₄] assemblies.