Distortion Engineering:\nA Strategy to Modulate Molecular\nUpconversion with Molecular Cluster-Aggregates

The rational engineering of molecules is a powerful chemistry\ntool\nof pivotal importance in the fields of molecular magnetism and luminescence.\nHence, systems that can be modulated via molecular engineering and\ncomposition control are expected to present extra versatility regarding\nthe tunability of their properties. This is the case with molecular\ncluster aggregates (MCAs), high nuclearity molecular compounds. Herein,\nwe demonstrate how the union of both strategies, namely, composition\ncontrol and molecular engineering, can be employed to enhance molecular\nupconversion in MCAs. This was achieved by doping a <b>{Gd</b><sub><b>8</b></sub><b>Er</b><sub><b>2</b></sub><b>Yb</b><sub><b>10</b></sub><b>}</b> MCA with\nCe<sup>III</sup> ions. By replacement of the optically silent Gd<sup>III</sup> ions with Ce<sup>III</sup>, the upconversion mechanism\nis modified due to Ce<sup>III</sup>-mediated cross-relaxation. In\naddition to this effect, we could also engineer the degree of metal\nsite distortion due to the larger size of Ce<sup>III</sup> ions, relaxing\nthe selection rules and impacting the upconversion quantum yield and\nluminescent thermometry. Opto-structural correlations demonstrate\nthat the presented molecular engineering strategy can be used to enhance\nthe performance of molecular upconverters.