The polynuclear Cu4I4py4 complex has been largely studied in solution and in the powder form due to its interesting luminescent properties, which are largely dependent on temperature and pressure. In this work, we present the synthesis of the complex and its wet impregnation in a mesoporous silica host obtained by sol-gel methodology. For optimized guest loadings, the well-dispersed guest molecules exhibit strong interaction with molecular oxygen, resulting in a significant quenching of the luminescence. The process is highly reversible with a Stern-Volmer constant of Ksv = 33.8, which is the largest value found in the literature for similar complexes in the solid state, suggesting that the new material is a promising candidate for high sensitivity oxygen sensing. Density Functional Theory (DFT) and Time-Dependent DFT (TD-DFT) calculations reveal a weak intermolecular interaction between two guest complexes in the excited state, suggesting the formation of an excited state complex (excimer). The assumption of triplet excimer formation is confirmed by temperature-and concentration-dependent experiments, which provides a new way to explain the giant Stokes shift observed for the guest complex in different media.

Ir III complexes are widely used in electroluminescent devices because of their appropriate photophysical properties. In the device, they can undergo supramolecular aggregation, which quenches their luminescence, as well as red shifts their emission, therefore downgrading the optical properties of the device. Here, we show that self-aggregation and red shift can be both prevented by designing new Ir III complexes using well- [a]

The Cover Feature shows how quantum chemical calculations help design novel IrIII complexes exhibiting improved photophysical properties: the use of different substituents (a–g) at specific positions prevents not only the red shift of the emission, but also the self‐aggregation. Both phenomena are well known to contribute to the downgrading of IrIII‐based luminescent devices. This work opens new possibilities for the smart design of luminescent compounds with optimized properties. More information can be found in the https://doi.org/10.1002/ejic.201800189