Encapsulation of Phosphorescent Pt(II) Complexes in Zn-Based Metal-Organic Frameworks toward Oxygen-Sensing Porous Materials Tim-Oliver Knedel, # Stefan Buss, # Iva ́ n Maisuls, Constantin G. Daniliuc, Carsten Schlü sener, Philipp Brandt, Oliver Weingart, Annette Vollrath, Christoph Janiak,* and Cristian A. Strassert* Cite This: Inorg. Chem. 2020, 59, 7252-7264 Read Online ACCESS Metrics & More Article Recommendations * sı Supporting Information ABSTRACT: 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 ( 3 MP-LC), [PtCN(L)] reached the highest phosphorescence quantum yields and displayed a significant sensitivity toward quenching by 3 O 2 . We encapsulated them into two Zn-based metal-organic frame- works, 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 3 O 2 - sensitive excited state lifetimes for the complexes at room temperature, reaching up to 18.4 μs under an Ar atmosphere, which is comparable with the behavior of the complex in liquid solutions or even frozen glassy matrices at 77 K. ■ INTRODUCTION Platinum(II)-based luminescent coordination compounds featuring a d 8 electronic configuration have been in the focus of research efforts due to their excited state properties and the applications derived from their phosphorescence. 1-11 Inter- system crossing into the triplet manifold and radiative relaxation from the lowest triplet state is facilitated by the significant spin-orbit coupling associated with the participa- tion of late transition elements in the electronic excited states, which constitutes a largely relativistic metal-based perturba- tion. The research fields span from catalysis, 1,2 bioimaging, 3-5 and biomedical applications 6,7 to uses in organic light emitting devices (OLEDs). 8-11 Due to their strong sigma-donating effect, cyclometalating luminophores greatly improve the photophysical properties (prolonged excited state lifetimes τ and increased photo- luminescence quantum yields Φ L ) by enhancing the ligand field splitting between occupied and empty d orbitals. Thus, the activation barrier for the thermal occupation of dissociative metal-centered excited states is enhanced, which in turn diminishes the population of electronic states that otherwise lead to radiationless relaxation favored by conical intersections with the ground state. 11 In this sense, significant advancements have been made in the design of improved coordination compounds. 12,13 Huo and co-workers showed that the change from a five-five-membered metallacycle system C^N^N to a six-five-membered metallacycle C^N*N system leads to higher Φ L due to better coordination geometries and orbital overlap. 14 These effects are further enhanced by removal of π- donating ancillary ligands and insertion of strong π acceptors, e.g., exchange of chlorido by cyanido units. For luminescent metal complexes with tridentate luminophoric ligands, the coligand can influence the solubility, and also the tendency toward aggregation can be modulated. 15,10 The ancillary ligand can also facilitate the covalent embedment into supramolecular assemblies for biomedical applications, as we have recently reported in collaboration with Gianneschi and co-workers regarding the use of a norbornene-substituted pyridine leading Received: March 4, 2020 Published: May 7, 2020 Article pubs.acs.org/IC © 2020 American Chemical Society 7252 https://dx.doi.org/10.1021/acs.inorgchem.0c00678 Inorg. Chem. 2020, 59, 7252-7264 Downloaded via DUESSELDORF LIBRARIES on May 22, 2020 at 06:12:56 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.