Room-Temperature Synthesis of Covalent Organic Frameworks with a Boronic Ester Linkage at the Liquid/Solid Interface.

With various prospected applications in the field of nanoelectronics and catalysis, on-surface synthesis of single-layer covalent organic frameworks (surface COFs) with designable structures and properties have attracted enormous interest. Herein, we report on a scanning tunneling microscopic investigation of the surface-confined synthesis of a covalently bonded boronic ester network directly at the octanoic acid/ highly oriented pyrolytic graphite(HOPG) interface under room temperature. The dynamic reaction process was investigated in detail. STM results indicate that the surface networks undergo structural evolution from a hybrid covalent/noncovalent multiwall porous network to single-wall hexagonal COF with the decrease of monomer concentration. Further experimental observation disclosed that the boronic ester-linked system is sensitive to instantaneous voltage pulses and the stimulation of the STM tip. In addition, the 1 H NMR spectra has further confirmed that the surface and octanoic acid may play important roles in promoting the reaction between 4,4'-phenylazobenzoyl diboronic acid (ABBA) and 2,3,6,7,10,11-hexahydroxytriphenylene (HHTP) building units.