Two‐Dimensional Boronate Ester Covalent Organic Framework Thin Films with Large Single Crystalline Domains for a Neuromorphic Memory Device

Abstract

Despite the recent progress in the synthesis of crystalline boronate ester covalent organic frameworks (BECOFs) in powder and thin‐film through solvothermal method and on‐solid‐surface synthesis, respectively, their applications in electronics, remain less explored due to the challenges in thin‐film processability and device integration associated with the control of film thickness, layer orientation, stability and crystallinity. Moreover, although the crystalline domain sizes of the powder samples can reach micrometer scale (up to ≈1.5 μm), the reported thin‐film samples have so far rather small crystalline domains up to 100 nm. Here we demonstrate a general and efficient synthesis of crystalline two‐dimensional (2D) BECOF films composed of porphyrin macrocycles and phenyl or naphthyl linkers (named as 2D BECOF‐PP or 2D BECOF‐PN) by employing a surfactant‐monolayer‐assisted interfacial synthesis (SMAIS) on the water surface. The achieved 2D BECOF‐PP is featured as free‐standing thin film with large single‐crystalline domains up to ≈60 μm2 and tunable thickness from 6 to 16 nm. A hybrid memory device composed of 2D BECOF‐PP film on silicon nanowire‐based field‐effect transistor is demonstrated as a bio‐inspired system to mimic neuronal synapses, displaying a learning–erasing–forgetting memory process.

Perspective towards atomic‐resolution imaging of two‐dimensional polymers

“…Alternatively, a bottom‐up synthetic route has emerged in the last few years. Air–water, 9,10 surfactant‐assisted air–water, 11‐14 as well as liquid–liquid interfaces 15 have been explored for the fabrication of 2D polymer thin films. The interfaces could act as efficient templates for 2D‐confined polymerization, affording thin films with the controlled thickness (from a monolayer to a few tens of nanometers) and defined crystallographic orientations.…”

A Rising Star from Two Worlds: Collaboration of COFs and ILs

“…[ 12 ] Until now, great efforts have been made in the development of COFs‐based functional materials and most of COFs were synthesized by solvothermal synthesis [ 13 ] and other methods were also proposed including ionothermal synthesis, [ 14 ] microwave synthesis, [ 15 ] mechanochemical synthesis, [ 16 ] and interfacial synthesis. [ 17 ] Due to the flexible designability and functionalization, COFs‐based composites can arise from a variety of possibilities to improve their application performances, [ 18 ] which is dominantly attributed to the combination of merits between COFs and functional components.…”

Ether-linked porphyrin covalent organic framework with broadband optical switch

“…In comparison with the three-dimensional (3D) COFs, the two-dimensional (2D) COFs are more promising because of two factors: (1) the degree of lateral conjugation from π orbitals present throughout the individual 2D layer and (2) the inherent π-π stacking between the two adjacent layers ( Bhunia et al., 2017 ). To construct such COFs that have suitable geometry, good structural and environmental stability, and unique functional behaviors as well, one need to choose suitable linkers and/or linkages to connect the selected organic building blocks together ( Geng et al., 2020 ; Kandambeth et al., 2019 ; Wang et al., 2019 ; Liang et al., 2020 ; Diercks et al., 2018 ; Keller et al., 2018 ; Shi et al., 2020 ; Li et al., 2019 ; Meng et al., 2020 ; Park et al., 2020 ; Feng et al., 2011 , 2012 ; Wan et al., 2011 ; Lin et al., 2015 ; Liao et al., 2016 ; Huang et al., 2019 ; Guan et al., 2019 ). However, the linkers or linkages used for the realization of COF materials are mainly limited to the B=N, C–N, B–O, C=N and C=C bonds.…”