Conjugated Microporous Polymers via Solvent-Free Ionothermal Cyclotrimerization of Methyl Ketones
Jaehwan Kim, Casandra M. Moisanu, Cara N. Gannett, Arjun Halder, José J. Fuentes-Rivera, Sean H. Majer, Kyle M. Lancaster, Alexander C. Forse, Héctor D. Abruña, Phillip J. Milner
Abstract
Conjugated microporous polymers (CMPs) are porous organic materials that display (semi)conducting behavior due to their highly π-conjugated structures. As such, they are promising next-generation materials for applications requiring both conductivity and porosity, such as supercapacitive energy storage and electrochemical sensing. However, most CMPs and related porous aromatic frameworks (PAFs) are currently prepared using expensive transition metal-based catalysts under solvothermal conditions, significantly increasing their manufacturing costs. Herein, we demonstrate that the ionothermal cyclotrimerization of methyl ketones via the aldol reaction represents a new strategy for the solvent-free synthesis of CMPs and PAFs. Specifically, we show that 1,3,5-triacetylbenzene and tetrakis(4-acetylphenyl)methane can be polymerized in molten zinc chloride to produce highly conjugated and microporous materials, as confirmed by 77 K N2 adsorption measurements in conjunction with UV–vis, Raman, and solid-state NMR spectroscopies. The CMP prepared from 1,3,5-triacetylbenzene demonstrates higher charge storage capacities (up to 172 F/g) than a commercially available supercapacitor carbon, reflecting the promise of cyclotrimerized CMPs for electrical energy storage applications.