ABSTRACT

NON-TECHNICAL SUMMARY

Sustaining the rapid advances of modern electronics and clean energy technologies requires continuous innovation and supply of easily accessible smart materials that can transport and store electrical charges in a programmable fashion. Owing to their synthetic accessibility, structural modularity, and functional tunability, metal?organic frameworks (MOFs) and covalent organic frameworks (COFs) hold great potentials to serve as active components of next-generation electronics and energy-storage devices. Electrical conductivity?a product of charge carrier concentration and mobility?however, remains one of the most elusive traits of MOFs and COFs, prompting researchers to devise new design and synthetic strategies to engineer this much desired electronic property in these crystalline framework materials. With support from the Solid State and Materials Chemistry program in the Division of Materials Research and the Established Program to Stimulate Competitive Research (EPSCoR), Prof. Saha and his research group at Clemson University are developing and implementing a new design strategy to promote long-range out-of-plane charge transport in two-dimensional (2D) MOFs and COFs by incorporating cofacially stacked alternating electron-rich (pi-donor) and electron-deficient (pi-acceptor) arrays and then exploiting their efficient through-space charge delocalization capability in these solid-state materials, which are expected to generate promising intrinsic conductivity. This research project is not only producing novel electrically conductive 2D MOFs and COFs with unique structures and compositions, but also creating an innovative design strategy that can simultaneously facilitate in-plane and out-of-plane charge transport in two orthogonal directions through the layered networks and pi-donor/acceptor stacks, respectively, and thus boost the bulk conductivity of these emerging smart materials. This NSF-funded project is also enabling the PI to develop skilled workforce for future innovations by engaging and mentoring graduate, undergraduate, postdoctoral, and high-school students in cutting-edge materials research, inspire underrepresented minorities to pursue higher education in STEM, and raise scientific awareness of the society through various education and outreach activities at local schools, science museums, and public forums.

TECHNICAL SUMMARY

Owing to their diverse potentials to serve as active components of modern electronics and energy storage devices, electrically conductive metal?organic frameworks (MOFs) and covalent organic frameworks (COFs) have emerged as most coveted and explored functional materials. Yet, electrical conductivity, which is a function of charge carrier concentration and charge mobility, remains one of the most elusive features of these porous crystalline framework materials chiefly because they often lack efficient charge transport pathways. In two-dimensional (2D) MOFs, electronic conduction can occur within the planes through coordination and conjugated pi-bonds and/or across the planes through pi-stacked layers, whereas in 2D COFs, the latter represent the primary transport pathways. The large disparities between in-plane and out-of-plane charge transport in two orthogonal directions often render the conductivity of these materials highly anisotropic (i.e., direction dependent) and dampen their overall bulk conductivity. To address these issues and simultaneously promote both in- and out-of-plane charge transport such that it leads to higher bulk conductivity in 2D MOFs and COFs, in this project supported by NSF's Solid State and Materials Chemistry (SSMC) Program, Prof. Sourav Saha and his research group at Clemson University are pursuing novel design and synthetic strategies where they incorporate built-in alternating pi-donor/acceptor stacks inside 2D layered frameworks that can facilitate out-of-plane charge transport, bringing this typically less efficient pathway on par with through-bond conduction pathways. Understanding how pi-donor/acceptor stacks consisting of different complementary pi-donor and acceptor units embedded in 2D MOFs and COFs affect their out-of-plane charge transport capability and thus the overall bulk conductivity is creating a new design strategy for next-generation electrically conductive MOFs and COFs. This project is also enabling the PI to fulfill his longstanding commitment to develop skilled workforce capable of leading future innovations by guiding diverse group of researchers to execute complex multifaceted research, motivate minority students to pursue higher education in STEMs, and raise a scientifically aware society through various outreach and educational activities in local community.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

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