Prerequisites and prospects for the development of novel systems based on the Keplerate type polyoxomolybdates for the controlled release of drugs and fluorescent molecules

Russian Chemical Bulletin - Synthetic approaches were proposed to the development of hybrid organic—inorganic systems based on giant Keplerate polyoxometalates (POM Mo132), biocompatible...     

Fundamental Aspects of Xanthene Dye Aggregation on the Surfaces of Nanocluster Polyoxometalates: H- to J-Aggregate Switching

The induced aggregation of the xanthene dye rhodamine B (RhB) on metal oxide centers belonging to the highly symmetric surfaces of precise nanoscale templates with Keplerate (Mo₁₃₂) or toroidal (Mo₁₃₈) structures has been studied. With the joint use of the Langmuir isotherm and full Stern–Volmer models, the thermodynamic reasons for dye adsorption on the nanocluster surface, such as a mixture of monomer, H-aggregate (H-dimer), and J-aggregate forms (which can coexist or switch one into another under the exact conditions), were established: this was shown through UV/Vis and fluorescence spectroscopies. By using the framework of the exciton model, it is shown that the angle (α) between the transition dipole moments of RhB is very sensitive to surface strain inside the dye sub-monolayer. As a result, it is possible to switch from H- to J-aggregates by the post-functionalization of polyoxometalate (POM)-RhB associates by the surfactant bilayer shell, which allows the surface strain to grow. Recommendations are provided for managing the appearance of H- or J-aggregates on metal oxide (or polyelectrolyte) surfaces during photovoltaic or bioimaging applications.