Indexed on: 28 Sep '16Published on: 28 Sep '16Published in: Journal of the American Chemical Society
Herein, we describe the selective formation of a discrete fused metallarhomboid and a triangle by the careful control of the shape and stoichiometry of the building blocks. A tetraphenylethylene (TPE) based tetra-pyridyl donor is exploited as the bridging component, and coordination immobilization of the TPE unit within the rigid metallacyclic frameworks efficiently suppresses its intramolecular rotational motions. As a result, the fused polygons are innately emissive in dilute solution, representing an alternative to aggregation-induced emission. Upon further molecular aggregation, these metallacycles display aggregation-induced enhanced emissions (AIEE). Interestingly, the fused rhomboid 7 shows a weaker fluorescence in dilute solutions relative to that of the fused triangle 8, while a reversal of emission intensities was observed in the aggregated state. These markedly different fluorescence efficacies are likely due to the differences in the shapes of the fused-polygons. Thus, this work shows that the properties of supramolecular coordination complexes (SCCs) can be affected by subtle structural factors, which can be controlled easily and precisely at the molecular level.