Ab initio Bethe-Salpeter equation calculations of light absorption and emission in the metal-organic framework Zn-MFU-4l

Zn-MFU-4l is a metal-organic framework whose light emission can be tuned via anion substitution and guest molecule intercalation. While photoluminescence experiments report light emission that is consistent with self-trapped excitons, the nature and character of the excitons is still far from clear. Here, we compute electronic structure, phonon spectrum, electron-phonon coupling, and optical properties with density functional theory and the ab initio GW-Bethe-Salpeter equation approach for a range of anions. From our calculation of the excitons and phonon spectrum, we assess what part of the framework is involved with exciton self-trapping, and evaluate which modifications to the metal-organic framework structure can change the emission properties of the self-trapped excitons.