(First Place Poster Award) Probing Charge Transport Mechanisms in 2D Metal Organic Frameworks
Authors: Nyakuchena James , Nyakuchena James 
Published: September 2023

Metal Organic Frameworks (MOFs) are a class of highly porous crystalline materials that are constructed from zero- or one-dimensional inorganic chains in combination with multitopic organic ligands.1 They have received great attention recently due to their large surface area, tunable porosity, and easy preparation, which lead to their versatile applications including gas storage2 and separation3, sensing4, catalysis5 and drug delivery6. The versatility of MOFs is further entrenched in the vast available design space offered by the enormous number of metal-linker combinations7, 8. However, majority of MOFs are insulators with very few of them showing appreciable electrical conductivity. The insulating nature of MOFs can be traced back to the starting materials used in constructing these hybrid materials9. Although conductive MOFs have been reported, very little information about the mechanism of charge transport is available.10-12 There are mainly two types of charge transport mechanism reported in such materials, hopping and band transport.13 Hopping mechanism is dominated by movement of charges from donor to acceptor moieties due to charge localization which exists at specific sites within the MOF.13 Band transport relies on delocalization of carriers throughout the valence and conduction bands.14 These mechanisms require low energy pathways for charge transport which are not present in MOFs. Recently, researchers have focused on two synthetic approaches from a chemical perspective to achieve such low energy pathways; through bond approach and through space approach.13 Ideally, both pathways can either lead to band or hopping transport. The through space mechanism utilizes non-covalent interactions like π-π stacking between organic linkers, which creates an extended pathway for charge delocalization usually pronounced in 2D MOFs.15, 16 Recent studies which have successfully quantified and identified charge carrier types in MOFs17 show that conductivity increases mainly with chemical oxidation signifying hole formation18, but mobility and directional charge transfer is still limited by geometry.19 Although the field of electrically conductive MOFs has experienced tremendous expansion in the last decade and yielded a variety of MOFs with high mobility and conductivity, majority of these works focus on material design principle and conductivity measurement, leaving the fundamental understanding of CT mechanism underexplored; yet the latter is essential for the further development of this class of materials to be exploited in optoelectronics, solar cells, and photocatalysis. I will present my progress in exploring CT mechanisms in 2D MOFs using advanced spectroscopic techniques.

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