Thermal control over phosphorescence or thermally activated delayed fluorescence in a metal–organic framework

By integrating a tailor-made donor–acceptor (D–A) ligand in a metal–organic framework (MOF), a material
with unprecedented features emerges. The ligand combines a pair of cyano groups as acceptors with four
sulfanylphenyls as donors, which expose each a carboxylic acid as coordination sites. Upon treatment with
zinc nitrate in a solvothermal synthesis, the MOF is obtained. The new material combines temperature-
assisted reverse intersystem crossing (RISC) and intersystem crossing (ISC). As these two mechanisms are
active in different temperature windows, thermal switching between their characteristic emission
wavelengths is observed for this material. The two mechanisms can be activated by both, one-photon
absorption (OPA) and two-photon absorption (TPA) resulting in a large excitement window ranging from
ultraviolet (UV) over visible light (VL) to near infrared (NIR). Furthermore, the emission features of the
material are pH sensitive, such that its application potential is demonstrated in a first ammonia sensor.