Sandwich-like Structure of Indole and Carbon Dioxide with Efficient CO2 Capture and Conversion

A hydroxyl-containing and aniline-functionalized indole-based microporous organic polymer (MOP) material poly(hydroxyl indole)-NH2 (PHOIN-NH2) has been successfully designed and synthesized. It was first proven that, due to the electron-rich benzene ring of the aniline group and the electron donor hydroxyl groups donating their electron density to the inner indole ring, the highly electron-rich pi indole plane can simultaneously attract two CO2 molecules via the double local dipole-pi interactions, thereby forming a "CO2-indole-CO2" sandwich-like structure and endowing this microporous material with a remarkable CO2, adsorption capacity (33 wt %). In addition, due to the classical acid-base interaction between the aniline group in the PHOIN-NH2 aerogel and the CO2 molecule, the resulting material displays excellent gas selectivity (CO2/N-2 = 146, CO2/CH4 = 24). Moreover, the phenolic-OH groups in the PHOIN-NH2 aerogel provide an abundance of sites for anchoring Zn2+ via metal-coordination interactions for effective conversion of CO2 into propylene carbonate.