New Synthetic Strategies Towards Carbene-Based Graphene Analogues
Abstract
Objectives: New families of atomically precise 2D materials will be synthesized, including wholly organic (covalent organic frameworks, COFs) and hybrid organic-inorganic (metal organic frameworks, MOFs) materials. To achieve this goal, the understudied chemistry of N-heterocyclic carbenes (NHCs), which are strongly nucleophilic molecules that have largely been use as anchoring groups in materials science, will be employed. Methods for their incorporation into COFs with highly tunable structures will be developed first, enabling studies into how NHC structure affects framework planarity and the extent of electronic delocalization. These findings will facilitate the synthesis of "impossible" NHC-linked MOFs, which are challenging to synthesize directly due to the strongly coordinating nature of NHCs. Last, dimensionally reduced macrocycle analogues of COFs and MOFs will be prepared, allowing for studying the properties of processable conjugated 0-dimensional molecules. Throughout, structure-property relationships will be interrogated to understand how framework structure affects properties such as optical band gaps, electronic conductivities, and redox activities. These studies will be supported by spectroscopic measurements and electronic structure calculations, as well as studies of molecular model systems. The successful completion of this research program will unlock a new family of conjugated materials for incorporation into next-generation devices. Methods: Materials will be characterized using a range of techniques, including X-ray diffraction, transmission electron diffraction, gas sorption analysis, UV-Vis spectroscopy, scanning Kelvin probe microscopy, infrared spectroscopy, energy dispersive X-ray spectroscopy, and solid-state nuclear magnetic resonance. Materials will be synthesized using the standard techniques of organic chemistry and materials science. Significance: 2-dimensional conjugated materials have transformed materials science, enabling new applications ranging from energy generation and storage to quantum information science to photocatalysis. However, the development of new, atomically precise 2D materials with tunable structures and optoelectronic properties remains a major challenge. Recent work has demonstrated that 2D MOFs and COFs offer a promising direction for the field due to their highly tunable and crystalline structures. However, only a limited handful of electronically conductive 2D MOFs have been prepared, and COFs are generally limited by the poor reversibility of the covalent bond-forming reactions used to synthesize them. In addition, both classes of materials face processing challenges due to their poor solubilities, and structure-property trends to guide the development of new materials remain scarce. The proposed research program will address all of these challenges. NHC-based COFs will offer unparalleled structural tunability, allowing for the synthesis of highly crystalline and well-defined 2D organic materials. Comparison to molecular models will guide studies into how structural planarity and interlayer stacking interactions impact the electronic conductivity of 2D COFs. These findings will be translatable to other families of 2D organic materials. NHC-based MOFs can be constructed with a large range of transition metals, allowing for one to "dial in" desirable properties based on choice of metal and NHC structure. Comparison to 0D macrocycles with analogous structures will facilitate an improved understanding of whether dimensional reduction can be employed to improve the processing of 2D materials without losing their desirable optoelectronic properties. These findings will facilitate the design of other 0D organic and hybrid materials.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 28, 2023
- Source ID
- W911NF2310128
Entities
People
- Phillip Milner
Organizations
- Army Contracting Command
- Cornell University
- United States Army