skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


  • NSF Public Access
  • Search Results
  • Design and synthesis of two-dimensional covalent organic frameworks with four-arm cores: prediction of remarkable ambipolar charge-transport properties
Title: Design and synthesis of two-dimensional covalent organic frameworks with four-arm cores: prediction of remarkable ambipolar charge-transport properties
We have considered three two-dimensional (2D) π-conjugated polymer network ( i.e. , covalent organic frameworks, COFs) materials based on pyrene, porphyrin, and zinc-porphyrin cores connected via diacetylenic linkers. Their electronic structures, investigated at the density functional theory global-hybrid level, are indicative of valence and conduction bands that have large widths, ranging between 1 and 2 eV. Using a molecular approach to derive the electronic couplings between adjacent core units and the electron-vibration couplings, the three π-conjugated 2D COFs are predicted to have ambipolar charge-transport characteristics with electron and hole mobilities in the range of 65–95 cm 2 V −1 s −1 . Such predicted values rank these 2D COFs among the highest-mobility organic semiconductors. In addition, we have synthesized the zinc-porphyrin based 2D COF and carried out structural characterization via powder X-ray diffraction, high-resolution transmission electron microscopy, and surface area analysis, which demonstrates the feasibility of these electroactive networks. Steady-state and flash-photolysis time-resolved microwave conductivity measurements on the zinc-porphyrin COF point to appreciable, broadband photoconductivity while transmission spectral measurements are indicative of extended π-conjugation.  more » « less
Award ID(s):
1708147
PAR ID:
10107051
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Materials Horizons
ISSN:
2051-6347
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; (, The Journal of Chemical Physics)
    Porous, stacked two-dimensional covalent organic frameworks (2D COFs) bearing semiconducting linkers can support directional charge transfer across adjacent layers of the COF. To better inform the current and possible future design rules for enhancing electron and hole transport in such materials, an understanding of how linker selection and functionalization affects interlayer electronic couplings is essential. We report electronic structure simulation and analysis of electronic couplings across adjacent linker units and to encapsulated species in functionalized electroactive 2D COFs. The detailed dependence of these electronic couplings on interlayer interactions is examined through scans along key interlayer degrees of freedom and through configurational sampling from equilibrium molecular dynamics on semiempirical potential energy surfaces. Beyond affirming the sensitivity of the electronic coupling to interlayer distance and orientation, these studies offer guidance toward linker functionalization strategies for enhancing charge carrier transport in electroactive 2D COFs. 
    more » « less
  2. ; ; ; ; ; (, Angewandte Chemie International Edition)
    Abstract Two covalent organic frameworks consisting of carbazolylene‐ethynylene shape‐persistent macrocycles with azine (MC‐COF‐1) or imine (MC‐COF‐2) linkages were synthesized via imine condensation. The obtained 2D frameworks are fully conjugated which imparts semiconducting properties. In addition, the frameworks showed high porosity with aligned accessible porous channels along the z axis, serving as an ideal platform for post‐synthetic incorporation of I2into the channels to enable electrical conductivity. The resulting MC‐COF‐1 showed an electrical conductivity up to 7.8×10−4 S cm−1at room temperature upon I2doping with the activation energy as low as 0.09 eV. Furthermore, we demonstrated that the electrical properties of both MC‐COFs are switchable between electron‐conducting and insulating states by simply implementing doping‐regenerating cycles. The knowledge gained in this study opens new possibilities for the future development of tunable conductive 2D organic materials. 
    more » « less
  3. ; (, Chemical Science)
    null (Ed.)
    Understanding the underlying physical mechanisms that govern charge transport in two-dimensional (2D) covalent organic frameworks (COFs) will facilitate the development of novel COF-based devices for optoelectronic and thermoelectric applications. In this context, the low-energy mid-infrared absorption contains valuable information about the structure–property relationships and the extent of intra- and inter-framework “hole” polaron delocalization in doped and undoped polymeric materials. In this study, we provide a quantitative characterization of the intricate interplay between electronic defects, domain sizes, pore volumes, chemical dopants, and three dimensional anisotropic charge migration in 2D COFs. We compare our simulations with recent experiments on doped COF films and establish the correlations between polaron coherence, conductivity, and transport signatures. By obtaining the first quantitative agreement with the measured absorption spectra of iodine doped (aza)triangulene-based COF, we highlight the fundamental differences between the underlying microstructure, spectral signatures, and transport physics of polymers and COFs. Our findings provide conclusive evidence of why iodine doped COFs exhibit lower conductivity compared to doped polythiophenes. Finally, we propose new research directions to address existing limitations and improve charge transport in COFs for applications in functional molecular electronic devices. 
    more » « less
  4. ; ; ; ; ; ; (, Angewandte Chemie International Edition)
    Abstract Covalent organic frameworks linked by carbon‐carbon double bonds (C=C COFs) are an emerging class of crystalline, porous, and conjugated polymeric materials with potential applications in organic electronics, photocatalysis, and energy storage. Despite the rapidly growing interest in sp2carbon‐conjugated COFs, only a small number of closely related condensation reactions have been successfully employed for their synthesis to date. Herein, we report the first example of a C=C COF, CORN‐COF‐1 (CORN=Cornell University), prepared byN‐heterocyclic carbene (NHC) dimerization. In‐depth characterization reveals that CORN‐COF‐1 possesses a two‐dimensional layered structure and hexagonal guest‐accessible pores decorated with a high density of strongly reducing tetraazafulvalene linkages. Exposure of CORN‐COF‐1 to tetracyanoethylene (TCNE,E1/2=0.13 V and −0.87 V vs. SCE) oxidizes the COF and encapsulates the radical anion TCNE⋅−and the dianion TCNE2−as guest molecules, as confirmed by spectroscopic and magnetic analysis. Notably, the reactive TCNE⋅−radical anion, which generally dimerizes in the solid state, is uniquely stabilized within the pores of CORN‐COF‐1. Overall, our findings broaden the toolbox of reactions available for the synthesis of redox‐active C=C COFs, paving the way for the design of novel materials. 
    more » « less
  5. ; ; ; ; (, Angewandte Chemie International Edition)
    Abstract Covalent organic frameworks (COFs) have received broad interest owing to their permanent porosity, high stability, and tunable functionalities. COFs with long‐range π‐conjugation and photosensitizing building blocks have been explored for sustainable photocatalysis. Herein, we report the first example of COF‐based energy transfer Ni catalysis. A pyrene‐based COF with sp2carbon‐conjugation was synthesized and used to coordinate NiIIcenters through bipyridine moieties. Under light irradiation, enhanced energy transfer in the COF facilitated the excitation of Ni centers to catalyze borylation and trifluoromethylation reactions of aryl halides. The COF showed two orders of magnitude higher efficiency in these reactions than its homogeneous control and could be recovered and reused without significant loss of catalytic activity. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email