A Perylene-Based Microporous Coordination Polymer Interacts Selectively with Electron-Poor Aromatics.

The design, synthesis, and properties of the new microporous coordination polymer UMCM-310 are described. The unique electronic character of the perylene-based linker enables selective interaction with electron-poor aromatics leading to efficient separation of nitroaromatics. UMCM-310 possesses high surface area and large pore size and thus permits the separation of large organic molecules based on adsorption rather than size exclusion.

Filling pore space in a microporous coordination polymer to improve methane storage performance.

A strategy that allows the tuning of pore size in microporous coordination polymers (MCPs) through modification of their organic linkers is presented. When large substituents are introduced onto the linker, these pendent groups partially occupy the pores, thus reducing pore size while serving as additional adsorption sites for gases. The approach takes advantage of the fact that, for methane storage materials, small pores (0.4-0.8 nm in diameter) are more desirable than large pores since small pores promote optimal volumetric capacity. This method was demonstrated with IRMOF-8, a MCP constructed from Zn4O metal clusters and 2,6-naphthalenedicarboxylate (NDC) linkers. The NDC was functionalized through the addition of substituents including tert-butylethynyl or phenylethynyl groups. High pressure methane uptake demonstrates that the IRMOF-8 derivatives have significantly better performance than the unfunctionalized material in terms of both excess volumetric uptake and deliverable capacity. Moreover, IRMOF-8 derivatives also give rise to stronger interactions with methane molecules as shown by higher heat of adsorption values.

Orientation and morphology control in acid-catalyzed covalent organic framework thin films.

As thin films of semiconducting covalent organic frameworks (COFs) are demonstrating utility for ambipolar electronics, channel materials in organic electrochemical transistors (OECTs), and broadband photodetectors, control and modulation of their thin film properties is paramount. In this work, an interfacial growth technique is utilized to synthesize imine TAPB-PDA COF films at both the liquid-liquid interface as well as at the liquid-solid interface on a Si/SiO2 substrate. The concentration of acetic acid catalyst in the aqueous phase is shown to significantly influence the thin film morphology of the liquid-solid growth, with concentrations below 1 M resulting in no film nucleation, concentrations of 1-4 M enabling smooth film formation, and concentrations greater than 4 M resulting in films with a higher density of particulates on the surface. Importantly, while the films grown at the liquid-liquid interface are mixed-orientation, those grown directly at the liquid-solid interface on the Si/SiO2 surface have highly oriented COF layers aligned parallel to the substrate surface. Moreover, this liquid-solid growth process affords TAPB-PDA COF thin films with p-type charge transport having a transconductance of 10 µS at a gate voltage of -0.9 V in an OECT device structure.

Microwave Facilitated Covalent Organic Framework/Transition Metal Dichalcogenide Heterostructures.

Organic/inorganic heterostructures present a versatile platform for creating materials with new functionalities and hybrid properties. In particular, junctions between two dimensional materials have demonstrated utility in next generation electronic, optical, and optoelectronic devices. This work pioneers a microwave facilitated synthesis process to readily incorporate few-layer covalent organic framework (COF) films onto monolayer transition metal dichalcogenides (TMDC). Preferential microwave excitation of the monolayer TMDC flakes result in selective attachment of COFs onto the van der Waals surface with film thicknesses between 1 and 4 nm. The flexible process is extended to multiple TMDCs (MoS2, MoSe2, MoSSe) and several well-known COFs (TAPA-PDA COF, TPT-TFA-COF, and COF-5). Photoluminescence studies reveal a power-dependent defect formation in the TMDC layer, which facilitates electronic coupling between the materials at higher TMDC defect densities. This coupling results in a shift in the A-exciton peak location of MoSe2, with a red or blue shift of 50 or 19 meV, respectively, depending upon the electron donating character of the few-layer COF films. Moreover, optoelectronic devices fabricated from the COF-5/TMDC heterostructure present an opportunity to tune the PL intensity and control the interaction dynamics within inorganic/organic heterostructures.