Abstract
The poor electrical conductivity of metal-organic frameworks (MOFs) has been a stumbling block for its applications in many important fields. Therefore, exploring a simple and effective strategy to regulate the conductivity of MOFs is highly desired. Herein, anionic guest molecules are incorporated inside the pores of a cationic MOF (PFC-8), which increases its conductivity by five orders of magnitude while maintaining the original porosity. In contrast, the same operation in an isoreticular neutral framework (PFC-9) does not bring such a significant change. Theoretical studies reveal that the guest molecules, stabilized inside pores through electrostatic interaction, play the role of electron donors as do in semiconductors, bringing in an analogous n-type semiconductor mechanism for electron conduction. Therefore, we demonstrate that harnessing electrostatic interaction provides a new way to regulate the conductivity of MOFs without necessarily altering the original porous structure. This strategy would greatly broaden MOFs' application potential in electronic and optoelectronic technologies.
Highlights
Exploration of electrically conductive metal-organic frameworks (MOFs) [1] offers exciting opportunities for fabricating electronic materials with the advantages of tunable structure, high crystallinity, and permanent porosity [2]
For the first time, gives clear evidence that the bands (Γ2′ and Γ3′) due to the intercalated molecular orbitals lie in the gap of the host MOF framework, and in particular, they lie very close to the conduction band edge in the present case
The approaching of the dopant bands from the Zn-S2- molecule to the conduction band makes it much easy to excite electrons from the dopant bands to the conduction bands by photons in a wide range of frequencies or even phonons, which increases largely the charge carrier concentration in the conduction band, and leads to a dramatic increase of the conductivity of the MOF material
Summary
Exploration of electrically conductive metal-organic frameworks (MOFs) [1] offers exciting opportunities for fabricating electronic materials with the advantages of tunable structure, high crystallinity, and permanent porosity [2]. The use of metal ions with partially occupied d orbitals (Fe, Cu) and ligands with heteroatoms (N, S) was found to increase the density of charge carriers and promote conductivity effectively [22,23,24] This approach usually relies on tedious syntheses of specific organic linkers to obtain a new material. An alternative one is to choose exogenous species to infiltrate into the pores of a MOF to modify its poor conductivity This method has the advantages of convenience and low cost. The feasibility of this method has been verified in several studies [25,26,27,28,29], the mechanism of the conductivity variation caused by the infilling of the guest molecules has yet to be well understood, which, is important, because it provides necessary information for designing and preparing new semiconductive MOFs with rich structural variations and modifiability
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