Photophysical study of [Ru(2,2′-bipyridine)3]2+ and [Ru(1,10-phenanthroline)3]2+ encapsulated in the Uio-66-NH2 metal organic framework

Confinement of Luminescent Guests in Metal-Organic Frameworks: Understanding Pathways from Synthesis and Multimodal Characterization to Potential Applications of LG@MOF Systems

This review gives an authoritative, critical, and accessible overview of an emergent class of fluorescent materials termed "LG@MOF", engineered from the nanoscale confinement of luminescent guests (LG) in a metal-organic framework (MOF) host, realizing a myriad of unconventional materials with fascinating photophysical and photochemical properties. We begin by summarizing the synthetic methodologies and design guidelines for representative LG@MOF systems, where the major types of fluorescent guest encompass organic dyes, metal ions, metal complexes, metal nanoclusters, quantum dots, and hybrid perovskites. Subsequently, we discuss the methods for characterizing the resultant guest-host structures, guest loading, photophysical properties, and review local-scale techniques recently employed to elucidate guest positions. A special emphasis is paid to the pros and cons of the various methods in the context of LG@MOF. In the following section, we provide a brief tutorial on the basic guest-host phenomena, focusing on the excited state events and nanoscale confinement effects underpinning the exceptional behavior of LG@MOF systems. The review finally culminates in the most striking applications of LG@MOF materials, particularly the "turn-on" type fluorochromic chemo- and mechano-sensors, noninvasive thermometry and optical pH sensors, electroluminescence, and innovative security devices. This review offers a comprehensive coverage of general interest to the multidisciplinary materials community to stimulate frontier research in the vibrant sector of light-emitting MOF composite systems.

Confinement-guided photophysics in MOFs, COFs, and cages

In this review, the dependence of the photophysical response of chromophores in the confined environments associated with crystalline scaffolds, such as metal-organic frameworks (MOFs), covalent-organic frameworks (COFs), and molecular cages, has been carefully evaluated. Tunability of the framework aperture, cavity microenvironment, and scaffold topology significantly affects emission profiles, quantum yields, or fluorescence lifetimes of confined chromophores. In addition to the role of the host and its effect on the guest, the methods for integration of a chromophore (e.g., as a framework backbone, capping linker, ligand side group, or guest) are discussed. The overall potential of chromophore-integrated frameworks for a wide-range of applications, including artificial biomimetic systems, white-light emitting diodes, photoresponsive devices, and fluorescent sensors with unparalleled spatial resolution are highlighted throughout the review.

Modulation of Osmium(II) Tris(2,2'-bipyridine) Photophysics through Encapsulation within Zinc(II) Trimesic Acid Metal Organic Frameworks

The Os(II) tris(2,2'-bipyridine) (OsBpy) complex exhibits optical properties that are particularly attractive for light harvesting systems due to the broad absorption spectrum extending throughout the solar spectrum. However, the relatively short lifetime of the triplet metal to ligand charge transfer state (³MLCT) relative to the related Ru(II)tris(2,2'-bipyridine) (RuBpy) has limited applications. Here, the encapsulation of OsBpy within two distinct Zn(II)-trimesic acid MOFs, HKUST-1(Zn) and USF-2 is demonstrated in an effort to extend the ³MLCT lifetime. Encapsulation results in a hypsochromatic shift of the steady-state emission band in both frameworks resulting from a destabilization of the ³MLCT. The encapsulated OsBpy also exhibits extended emission lifetimes in both HKUST-1(Zn) (104 ns in MOF vs 50 ns in methanol) and USF-2 (81 ns in MOF vs 50 ns in methanol) arising from changes in the nonradiative decay constants in both systems. The data are also consistent with vibronic perturbations involved in mixing between higher energy ³MLCT* and ligand field states.