Understanding Diffusional Charge Transport within a Pyrene-Based Hydrogen-Bonded Organic Framework

Abstract

Electrochemically active hydrogen-bonded organic frameworks (HOFs) offer opportunities to study charge transport in supramolecular systems where the rate of movement of charges is dependent on weak electronic coupling between individual components. Here, we used potential-step chronoamperometric measurements on electrochemically active, drop-cast HOF-102 films to estimate both redox-hopping-based apparent diffusion coefficients for charge transport and rate constants for linker-to-linker charge transfer (hole transfer) in the mesoporous twodimensional (2D) plane created by interlinker hydrogen bonding. Also present are one-dimensional columns formed by stacking pyrene units. However, because the HOF-102 crystallites containing these columns are oriented parallel to an underlying electrode, dynamics of charge transport (hole-transport) along the column axis, in contrast to the plane, are not directly probed by the electrochemical measurements. Furthermore, we employed electrochemical impedance spectroscopy to measure the electrical conductivity of the as-deposited films biased at various potentials. We found that both the neutral/singly oxidized and the singly oxidized/doubly oxidized pyrene linker redox couples of HOF-102 can engender hoppingbased film conductivity within the 2D plane of HOF-102. Consistent with the radical cation and radical dication nature of the singly and doubly oxidized linkers, respectively, HOF-102 films are electrochromic. The measured values of in-plane charge-diffusion coefficients (∼10 −10 to 10 −11 cm 2 s −1 ) and electrical conductivity (∼10 −6 to 10 −8 S cm −1 ) compare favorably with those for related redox-conductive MOFs and suggest that the transport and conductivity parameters for HOF-102 are sufficiently large to support electrocatalysis by subsequently installed catalysts in filmsspecifically, films of micron or greater thickness, corresponding to the equivalent hundreds of monolayers of closely packed (i.e., face-to-face-packed) pyrene-derivatives, but with solution access (solvent, ion, and reactant access) still readily provided by channels oriented parallel to an underlying planar electrode.

Interlayer electron coupling pathway driven electrochemiluminescence in hydrogen-bonded organic frameworks

“…The cathodic ECL intensities of HOF-101 and HOF-100 were enhanced to 9.1 and 3.5 folds than those of TCPPY and TCPY ligands (Supplementary Figs. 25,26). Interestingly, the ECL e ciency of HOF-101/K 2 S 2 O 8 was as high as 64.7% compared with 0.1 mM Ru(bpy) 3 2+ /TPrA system (Supplementary Fig.…”

“…interactive charge transfer for uorescence sensing 25 and electrochromism 26 . A label free ECL biosensor for assay of kanamycin was constructed based on triazinyl HOF self-assembled by N•••H hydrogen bond aggregation with a relative ECL e ciency of 21.3% 27 .…”

Robust Mesoporous Functional Hydrogen-Bonded Organic Framework for Hypochlorite Detection

“…In view of the above-mentioned merits, HOFs have been widely exploited as multifunctional materials for gas storage and separation, − sensing, − heterogeneous catalysis, − proton conduction, , biological applications, − etc. − The development of HOFs, however, still far lags behind their MOF and COF counterparts. The main reasons include their low stability (especially in water media), very small/none pores, and difficult functionality, resulting from the nature of intermolecular forces ( i.e.…”

Intrareticular electron coupling pathway driven electrochemiluminescence in hydrogen-bonded organic frameworks

“…[21][22][23] The strong p-p stacking interactions among interlayer conjugated units improve the stability of HOFs. 24,25 IREC in the HOF structure enables interactive charge transfer for fluorescence sensing 26 and electrochromism. 27 Furthermore, by integrating functional monomers into frameworks, 28 the long-range ordered HOF structure could accelerate charge transfer for the formation of excited-state HOF species during ECL generation.…”