Formation Mechanisms and Defect Engineering of Imine-Based Porous Organic Cages

• Published in: Chemistry of materials 2017-12, Vol.30 (1)
• Main Authors: Zhu, Guanghui, Liu, Yang, Flores, Luis, Lee, Zachary R., Jones, Christopher W., Dixon, David A., Sholl, David S., Lively, Ryan P.
• Format: Article
• Language: English
• Subjects: carbon capture; catalysis (heterogeneous); defects; INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; materials and chemistry by design; membrane; synthesis (novel materials); synthesis (scalable processing); synthesis (self-assembly)
• ISSN: 0897-4756; 1520-5002

The syntheses of porous organic cages (POCs) represent an important synthetic puzzle in dynamic covalent chemistry based self-sorting. Improved understanding of the formation mechanisms of POCs can lead to control and rational design of cages with desired functionality. Herein, we explore the formation mechanisms of imine-based POCs using time-resolved electrospray mass spectrometry, and electronic structure calculations at the density functional theory and correlated molecular orbital theory levels. We find that the synthesis of the [4+6] cycloimine cage CC3-R and the [2+3] cycloimine cage CC-pentane both proceed through similar intermediates via a series of consecutive reactions. The proposed reaction mechanisms are supported by electronic structure calculations. Based on our observations from both experiments and calculations, we propose a comprehensive method for designing and predicting new POC species. In addition, the observation of stable incomplete cages during CC3-R synthesis inspired us to design intentionally defective cages. These “missing-linker” type molecular defects are installed into CC3-R via non-solvent induced crystallization. The defective CC3-R materials are found to have enhanced CO2 interaction and improved CO2 uptake capacity due to the additional functional groups present within the CC3 crystals.