Humidity Sensing through Reversible Isomerization of a Covalent Organic Framework

Samik Jhulki, Austin M. Evans, Xue Li Hao, Matthew W. Cooper, Cameron H. Feriante, Johannes Leisen, Hong Li, David Lam, Mark C. Hersam, Stephen Barlow, Jean Luc Brédas, William R. Dichtel*, Seth R. Marder

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

196 Scopus citations


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 languageEnglish (US)
Pages (from-to)783-791
Number of pages9
JournalJournal of the American Chemical Society
Issue number2
StatePublished - Jan 15 2020

ASJC Scopus subject areas

  • General Chemistry
  • Biochemistry
  • Catalysis
  • Colloid and Surface Chemistry


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