Photoinduced: Versus spontaneous host-guest electron transfer within a MOF and chromic/luminescent response

A novel Eu(iii) metal-organic framework (MOF) featuring 3-fold interpenetration shows multi-responsive behaviors owing to the combination of charge transfer, electron transfer, and energy transfer between different ingredients (the electron-deficient tris(pyridinium)triazine (tpt) chromophore, the electron-rich naphthalene chromophore, the Eu(iii) luminophore, and the guest anion). The interframework naphthalene-to-tpt charge transfer dictated by framework interpenetration serves to sensitize the Eu(iii) emission through energy transfer. The photoinduced host-guest electron transfer from the intrinsic chloride guest to tpt leads to photochromism and photoquenching of photoluminescence. The spontaneous host-guest electron transfer from extrinsic amine/ammonia to tpt allow chromic and luminescent response to ammonia and amines with size selectivity. Furthermore, the photogenerated phase shows sensitive color change and luminescence turn-on upon exposure to O2. The multi-responsive properties offer the appeal for optical switching and sensing use. The qualitative and quantitative gaseous sensing of ammonia and O2 has been demonstrated with portable and reusable MOF-polymer membranes.