On the Existence of Excitonic Signatures in the Optical Response of Metal-Organic Frameworks: Comment on "van der Waals Metal-Organic Framework as an Excitonic Material for Advanced Photonics".

In a recent experimental paper, it was claimed that pronounced excitonic signatures are observed in optical response of Zn-based metal-organic frameworks (MOFs) at room temperature. Performing ab initio modelling, it is demonstrated that an alternative interpretation based on single-electron optical transitions between narrow π-bands in the system of aromatic rings of the ligand is far more plausible. Although these results do not rule the possibility of exciton formation in MOFs out completely, they show that extreme caution should be taken in attributing the features in photoabsorption spectra alone to excitons, and additional proof, such as data on long-distance energy transfer, is necessary.