Enhancing Dynamic Spectral Diffusion in Metal-Organic Frameworks Through Defect Engineering

Abstract

The crystal packing of organic chromophores has a profound impact on their photophysical properties. Molecular crystal engineering is generally incapable of producing precisely spaced arrays of molecules for use in photovoltaics, light-emitting diodes, and sensors. A promising alternative strategy is the incorporation of chromophores into crystalline metal-organic frameworks (MOFs), leading to matrix coordination-induced emission (MCIE) upon confinement. However, it remains unclear how the precise arrangement of chromophores and defects dictates photophysical properties in these systems, limiting the rational design of well-defined photoluminescent materials. Herein, we report new, robust Zr-based MOFs constructed from the linker tetrakis(4-carboxyphenyl)ethylene (TCPE4−) that exhibit an unexpected structural transition in combination with a prominent shift from green to blue photoluminescence (PL) as a function of the amount of acid modulator (benzoic, formic, or acetic acid) used during synthesis. Time-resolved PL (TRPL) measurements provide full spectral information and reveal that the observed hypsochromic shift arises due to a higher concentration of linker substitution defects at higher modulator concentrations, leading to broader excitation transfer-induced spectral diffusion. Spectral diffusion of this type has not been reported in a MOF to date, and its observation provides structural information that is otherwise unobtainable using traditional crystallographic techniques. Our findings suggest that defects have a profound impact on the photophysical properties of MOFs, and that their presence can be readily tuned to modify energy transfer processes within these materials.

Synthesis, structure and photoluminescence properties of heterometallic-based coordination polymers of trimesic acid

“…Coordination polymers (CPs) have garnered significant interest in crystal chemistry and materials science due to their intriguing structures and potential applications in various fields. These include catalysis (Adamji et al, 2023;Suremann et al, 2023;Wu et al, 2023;Xu et al, 2022), adsorption and separation (Chen et al, 2023;Daglar et al, 2021;Keasler et al, 2023;Liang et al, 2023), fluorescence sensing (Halder et al, 2023;Li et al, 2023), magnetism (Castro et al, 2022;Dong et al, 2023;Weng et al, 2011;Xu et al, 2023), and so on (Biswas et al, 2021;Naskar et al, 2017;Paul et al, 2017). The development of these CPs is commonly recognised to be predominantly influenced by the characteristics of the organic building blocks, the coordination geometry of the inorganic metal nodes and several synthetic parameters (Batten et al, 2016;Han et al, 2014;Rosa et al, 2016).…”