Direct observation of x-ray excited optical luminescence from a Re6 metal cluster in true aqueous solution: The missing link between material characterization and in vivo applications

Phosphorescent octahedral metal cluster complexes are highly attractive in terms of biomedical applications, particularly in the area of luminescent diagnostics and photodynamic therapy (PDT). The ability of clusters to be excited by x-radiation followed by red/near infrared emission makes them a new promising class of photosensitizers for deep-PDT. This work demonstrates a direct observation of x-ray-excited optical luminescence of hexanuclear clusters, by example of rhenium cluster complex Na4[{Re6Se8}(CN)6], in a true aqueous solution. The article also describes point-by-point the details and pitfalls of studying cluster radioluminescence in aqueous solution.