Abstract
Here we report that a covalent organic framework (COF), which contains 2,5-di(imine)-substituted 1,4-dihydroxybenzene (diiminol) moieties, undergoes color changes in the presence of solvents or solvent vapor that are rapid, passive, reversible, and easily detectable by the naked eye. A new visible absorption band appears in the presence of polar solvents, especially water, suggesting reversible conversion to another species. This reversibility is attributed to the ability of the diiminol to rapidly tautomerize to an iminol/cis-ketoenamine and its inability to doubly tautomerize to a diketoenamine. Density functional theory (DFT) calculations suggest similar energies for the two tautomers in the presence of water, but the diiminol is much more stable in its absence. Time-dependent DFT calculations confirm that the iminol/cis-ketoenamine absorbs at longer wavelength than the diiminol and indicate that this absorption has significant charge-transfer character. A colorimetric humidity sensing device constructed from an oriented thin film of the COF responded quickly to water vapor and was stable for months. These results suggest that tautomerization-induced electronic structure changes can be exploited in COF platforms to give rapid, reversible sensing in systems that exhibit long-term stability.
Original language | English (US) |
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Pages (from-to) | 783-791 |
Number of pages | 9 |
Journal | Journal of the American Chemical Society |
Volume | 142 |
Issue number | 2 |
DOIs | |
State | Published - Jan 15 2020 |
Funding
We thank the United States Army Research Office for a Multidisciplinary University Research Initiative (MURI) award under grant number W911NF-15-1-0447. S.J. thanks the United States-India Educational Foundation (USIEF, India) and the Institute of International Education (IIE, USA) for a Fulbright-Nehru Postdoctoral Fellowship (grant no. 2266/FNPDR/2017). A.M.E. is supported by the National Science Foundation Graduate Research Fellowship under grant no. (DGE-1324585). H.L. and J.-L.B. acknowledge funding of this work by the United States Army Research Office under award W911NF-17-10339. D.L. and M.C.H. acknowledge the Department of Energy (grant DE-SC0019356) for support of the Raman spectroscopy characterization. We thank Jeremy Swartz for videography assistance. Portions of this work were performed at the DuPont-Northwestern-Dow Collaborative Access Team (DND-CAT) located at Sector 5 of the Advanced Photon Source (APS). DND-CAT is supported by Northwestern University, E.I. DuPont de Nemours & Co., and The Dow Chemical Company. Grazing incidence diffraction patterns were collected at Sector 8 ID-E of the APS. This research used resources of the Advanced Photon Source, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under contract no. DE-AC02-06CH11357.
ASJC Scopus subject areas
- Catalysis
- General Chemistry
- Biochemistry
- Colloid and Surface Chemistry