Near-Infrared Photonic Metal–Organic Frameworks

ConspectusNear-infrared (NIR) light, especially NIR-II light (1000-2000 nm), has shown extensive applications in military and civilian fields such as night vision, biomedicine, optical communication, and noninvasive detection due to its superior penetration capabilities, invisibility to human eyes, less background interference, and low optical loss in optical fibers. The development of photonic materials that can absorb or emit NIR light thus has attracted great interest. Recently, metal-organic frameworks (MOFs), which were assembled by metal nodes and organic ligands, have emerged as particularly exciting crystalline porous materials due to their prospective applications in various fields, such as gas storage and separation, chemical sensing, catalysis, proton conduction, and drug delivery. The abundant and tailorable structures, as well as permanent porosity of MOFs, render them highly promising for NIR photonic applications. MOFs allow the rational and tunable design of NIR photonic materials by the judicious incorporation of NIR-responsive inorganic and organic units with the desired functionalities. In addition, the permanent porosity of MOFs greatly extends their opportunities toward NIR photonic materials. As ordered porous materials, MOFs are able to encapsulate diverse NIR-responsive photonic species, such as lanthanide ions, organic dyes, metal complexes, perovskite quantum dots, lanthanide-doped nanoparticles, etc., into the pores or structural-defect spaces for novel NIR photonic properties. More importantly, the well-organized and tunable pores can provide identical secondary environments around photonic species and control the intermolecular interactions as well as energy/charge transfer process between guests and MOFs, thus bringing much flexibility to pursue excellent or novel NIR photonic properties.In this Account, we summarize our recent efforts in the design and construction of NIR photonic MOFs, including mixed-lanthanide MOFs, multivariate-ligand MOFs, dye-encapsulated MOFs, and nanoparticle/MOF composites, as well as their unique NIR photonic performances and various applications. We first review the design strategies and advantages of NIR photonic MOFs, and then we focus on describing the key NIR photonic functionalities in MOFs, including NIR photoluminescence, NIR-II excited multiphoton luminescence, NIR-II pumped multiphoton lasing, NIR-II harmonic frequency, and NIR-II responsive multiple nonlinear optical (NLO) behaviors. Furthermore, we discuss the applications of NIR photonic MOFs in luminescent temperature sensing, three-dimensional patterning, photonic data storage, micronano lasing, and biological imaging. Finally, we outline our perspectives on the current challenges as well as the future development of NIR photonic materials. This Account gives a comprehensive understanding of NIR photonic MOFs and thereby will be helpful to promote MOF materials to step up from fundamental synthesis to promising applications in luminescent sensing, lasing devices, data storage, photonic integrated circuits, and biomedicine.