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Charge-transfer interactions between fullerenes and a mesoporous tetrathiafulvalene-based metal-organic framework.

ABSTRACT: The design of metal-organic frameworks (MOFs) incorporating electroactive guest molecules in the pores has become a subject of great interest in order to obtain additional electrical functionalities within the framework while maintaining porosity. Understanding the charge-transfer (CT) process between the framework and the guest molecules is a crucial step towards the design of new electroactive MOFs. Herein, we present the encapsulation of fullerenes (C₆₀) in a mesoporous tetrathiafulvalene (TTF)-based MOF. The CT process between the electron-acceptor C₆₀ guest and the electron-donor TTF ligand is studied in detail by means of different spectroscopic techniques and density functional theory (DFT) calculations. Importantly, gas sorption measurements demonstrate that sorption capacity is maintained after encapsulation of fullerenes, whereas the electrical conductivity is increased by two orders of magnitude due to the CT interactions between C₆₀ and the TTF-based framework.

SUBMITTER: Souto M

PROVIDER: S-EPMC6774073 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Charge-transfer interactions between fullerenes and a mesoporous tetrathiafulvalene-based metal-organic framework.

Souto Manuel M Calbo Joaquín J Mañas-Valero Samuel S Walsh Aron A Mínguez Espallargas Guillermo G

Beilstein journal of nanotechnology 20190918

The design of metal-organic frameworks (MOFs) incorporating electroactive guest molecules in the pores has become a subject of great interest in order to obtain additional electrical functionalities within the framework while maintaining porosity. Understanding the charge-transfer (CT) process between the framework and the guest molecules is a crucial step towards the design of new electroactive MOFs. Herein, we present the encapsulation of fullerenes (C<sub>60</sub>) in a mesoporous tetrathiafu ...[more]

PMID: 31598454

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Project description:Achieving a molecular-level understanding of how the structures and compositions of metal-organic frameworks (MOFs) influence their charge carrier concentration and charge transport mechanism-the two key parameters of electrical conductivity-is essential for the successful development of electrically conducting MOFs, which have recently emerged as one of the most coveted functional materials due to their diverse potential applications in advanced electronics and energy technologies. Herein, we have constructed four new alkali metal (Na, K, Rb, and Cs) frameworks based on an electron-rich tetrathiafulvalene tetracarboxylate (TTFTC) ligand, which formed continuous π-stacks, albeit with different π-π-stacking and S⋯S distances (d π-π and d S⋯S). These MOFs also contained different amounts of aerobically oxidized TTFTC˙+ radical cations that were quantified by electron spin resonance (ESR) spectroscopy. Density functional theory calculations and diffuse reflectance spectroscopy demonstrated that depending on the π-π-interaction and TTFTC˙+ population, these MOFs enjoyed varying degrees of TTFTC/TTFTC˙+ intervalence charge transfer (IVCT) interactions, which commensurately affected their electronic and optical band gaps and electrical conductivity. Having the shortest d π-π (3.39 Å) and the largest initial TTFTC˙+ population (∼23%), the oxidized Na-MOF 1-ox displayed the narrowest band gap (1.33 eV) and the highest room temperature electrical conductivity (3.6 × 10-5 S cm-1), whereas owing to its longest d π-π (3.68 Å) and a negligible TTFTC˙+ population, neutral Cs-MOF 4 exhibited the widest band gap (2.15 eV) and the lowest electrical conductivity (1.8 × 10-7 S cm-1). The freshly prepared but not optimally oxidized K-MOF 2 and Rb-MOF 3 initially displayed intermediate band gaps and conductivity, however, upon prolonged aerobic oxidation, which raised the TTFTC˙+ population to saturation levels (∼25 and 10%, respectively), the resulting 2-ox and 3-ox displayed much narrower band gaps (∼1.35 eV) and higher electrical conductivity (6.6 × 10-5 and 4.7 × 10-5 S cm-1, respectively). The computational studies indicated that charge movement in these MOFs occurred predominantly through the π-stacked ligands, while the experimental results displayed the combined effects of π-π-interactions, TTFTC˙+ population, and TTFTC/TTFTC˙+ IVCT interaction on their electronic and optical properties, demonstrating that IVCT interactions between the mixed-valent ligands could be exploited as an effective design strategy to develop electrically conducting MOFs.

Dataset Information

Charge-transfer interactions between fullerenes and a mesoporous tetrathiafulvalene-based metal-organic framework.

Publications

Charge-transfer interactions between fullerenes and a mesoporous tetrathiafulvalene-based metal-organic framework.

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