Highly Hydrophobic and Chemically Rectifiable Surface‐Anchored Metal‐Organic Framework Thin‐Film Devices

Abstract

(MOFs) in common organic solvents which heavily limits thin-film processing on various support substrates for fabrication of devices. SURMOFs are in principle possible to achieve virtually on any support including flexible plastic and cloth substrates with molecular-level control of the dimensionality as well as functionality. [2] Subsequent loading of guest molecules opens-up an immense opportunity of SURMOFs for applications in storage and separation of gas and liquid, making highly specific sensors, performing unconventional catalysis, and overall, for the development of stimuli responsive electronic and magnetic thin-film devices. [3] As for the electronic applications of metal-organics, the experimental challenges are, in general, i) patterning feasibility as thin-films by employing standard lithographic techniques, ii) controllable thickness and orientation, iii) film homogeneity, iv) reasonable porosity, v) desirable electrical conductivity, vi) tuning electrical conductivity of thin-films by physical and chemical stimuli, and finally, vii) stability of the thin-films at ambient conditions, specifically against moisture and heat. At a glance, SURMOFs appear suitable platforms to overcome all these challenges to a considerable extent except the facts that MOFs are i) intrinsically poor conductors of electricity (due to insulating nature of the organic ligands and an energy mismatch in the overlap between ligand's p orbitals and metal ion's d orbitals); and ii) usually nonhydrophobic and sensitive to moisture. [4] Such important issues bring to the origin of this work: How to fabricate SURMOF thin-film devices hydrophobic as well electrically conductive?In order to achieve reasonably good electrical conductivity, so far, HKUST-1-based (a porous metal-organic coordination polymer comprised of Cu ion and 1,3,5-benzene tricarboxylic acid (BTC) ligand (benzene tricarboxylic acid) SURMOF thinfilm device was infiltrated with organic electrophile guest tetracyanoquinodimethane (TCNQ) and the subsequent redoxreaction between Cu 2+ ions and TCNQ molecules resulted in a significant increase in the conductivity value within the semiconducting span. [5] However, HKUST-1-based SURMOF thin-films are not really hydrophobic. Another disadvantage

Achieving current rectification ratios ≥ 105 across thin films of coordination polymer

“…2a). Apart from the distinctive chemical identity, a notable difference between the surface morphological features of pristine and doped Cu-BTEC thin lms is the presence of a reasonably higher number of air-pockets in the latter compared to the former system that could generate highly hydrophobic surfaces 32 as was observed in respective zoomed-in FE-SEM images (Fig. S1 †).…”

“…S16 †). 32,53 The Raman band of pristine Cu-TCNQ at 520 cm À1 (perhaps due to the Cu/Cu interaction mode) was absent in our doped thin lm (Fig. S17 †).…”

Origin of the Chemiresistive Response of Ultrathin Films of Conductive Metal–Organic Frameworks

“…The rise of electrically conductive metal–organic frameworks (MOFs) has positioned these coordination frameworks, traditionally considered insulating, as promising alternatives to classical conductive materials for the development of electronic devices . The combination of high crystallinity, chemical versatility, and porosity with electrical conductivity makes them appealing candidates for energy storage platforms, field‐effect transistors (FETs), Schottky barrier diodes, thermoelectrics, resistive random‐access memories, rectifiers, or ion‐to‐electron transducers . Besides the search for new materials, research efforts have centered in gaining chemical control over their design to optimize the electrical conductivity.…”

Role of Water in the Dynamic Crystallization of CuTCNQ for Enhanced Redox Catalysis (TCNQ = Tetracyanoquinodimethane)

“…A recent study has shown that mixing MeCN with H 2 O has significant influence over the thermodynamic (vapor pressure, softness parameter, excess molar Gibbs energy, and enthalpy of mixing), surface tension, viscosity, polarity, and acidity/basicity properties of the resultant mixture . In addition, the aprotic/protic solvent mixture would also lead to a significant change in the dielectric environment . In our case, we believe that when water is added to MeCN, the changes in these properties of the reaction medium slows down the reaction kinetics, which in turn plays an important role in modulating the kinetics of CuTCNQ crystallization and dissolution.…”