Encapsulation of Phosphorescent Pt(II) Complexes in Zn-Based Metal-Organic Frameworks toward Oxygen-Sensing Porous Materials

In this work, we synthesized two tailored phosphorescent Pt(II) complexes bearing a cyclometalating tridentate thiazole-based C<^>N*N pincer luminophore (L) and exchangeable chlorido ([PtCl(L)]) or cyanido ([PtCN(L)]) coligands. While both complexes showed photoluminescence from metal-perturbed ligand-centered triplet states ((MP)-M-3-LC), [PtCN(L)] reached the highest phosphorescence quantum yields and displayed a significant sensitivity toward quenching by O-3(2). We encapsulated them into two Zn-based metal-organic frameworks, namely, MOF-5 and ZIF-8. The incorporation of the organometallic compounds in the resulting composites [PtCl(L)]@ZIF-8, [PtCN(L)]@ZIF-8, [PtCl(L)]@moF-5, and [PtCN-(L)]@MOF-5 was verified by powder X-ray diffractometry, scanning electron microscopy, time-resolved photoluminescence spectroscopy and microscopy, as well as N-2- and Ar-gas sorption studies. The amount of encapsulated complex was determined by graphite furnace atomic absorption spectroscopy, showing a maximum loading of 3.7 wt %. If compared with their solid state forms, the solid-solution composites showed prolonged O-3(2)-sensitive excited state lifetimes for the complexes at room temperature, reaching up to 18.4 mu s under an Ar atmosphere, which is comparable with the behavior of the complex in liquid solutions or even frozen glassy matrices at 77 K.