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

Abstract

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.

Luminescent MOFs (LMOFs): recent advancement towards a greener WLED technology

“…[113][114][115] Dye encapsulated in MOFs is an efficient method to restore the emission properties of dyes in the solid-state because of restricted aggregation caused quenching (ACQ) of the dyes by a confinement effect inside the pores of the MOFs. 116 Such dye@MOF composites thus have been used efficiently for generation of pure white light with a high quantum efficiency and CRI. A list of some common dyes which have been encapsulated in MOF structures for various opto-electronic applications including WLE is given in Fig.…”

Acridine based metal–organic framework host–guest featuring efficient photoelectrochemical-type photodetector and white LED

“…0.2-3 nm), LMOFs can be fabricated by encapsulation of a variety of luminescent guests (such as organic dyes, metal ions, metal complexes, metal nanoclusters, quantum dots, and hybrid perovskites), which usually provides certain advantages over traditional syntheses of luminescent materials. 31 For example this method broadens the light-harvesting region then enhancing the photoelectric performance, realizes multicolor fluorescence/phosphorescence emission, and minimizes the aggregation-caused quenching (ACQ) phenomena via confinement of dye guests into the pores of the crystalline MOF host. 32 However, to date, despite the promising results recently obtained on the photophysical properties of Guest@MOF, obtaining precise crystallographic information of guests encapsulated into the MOF host still remains a huge challenge.…”

“…[33][34][35] More studies on the relationship between the spatial positioning of guests, host-guest or guest-guest interactions, energy/ charge transport (Scheme 1) and photoelectric properties need to be carried out. 31,36 In this paper, we select the 5-ethoxyisophthalat acid (EtOIPA) ligand as the building block and acridine (AD) as the template to construct a new type of MOF host-guest system. Our previous works demonstrated that iso-phthalic acid (IPA) derivatives with bulk steric hindrance substituents at the 5-position favor the formation of metal clusters.…”

“…33–35 More studies on the relationship between the spatial positioning of guests, host–guest or guest–guest interactions, energy/charge transport (Scheme 1) and photoelectric properties need to be carried out. 31,36…”

Turn-On Fluorescence Chemical Sensing through Transformation of Self-Trapped Exciton States at Room Temperature

“…Although the turn-off type sensing by fluorescence quenching has its own advantages, 9 such as the ease of practical implementations, 2 this approach poses two major limitations which are worth addressing. The first is that the side effects of environmental interference cannot be efficiently ruled out.…”