Two-dimensional conjugated polymers synthesized via on-surface chemistry

Abstract

Two-dimensional materials (2DMs) are an important subject in material science that have many interesting physical properties and significant potential applications in various technological areas [1,2]. Since the successful exfoliation of monoatomic graphene by Novoselov et al. [3] in 2004, a series of inorganic 2DMs, including transition-metal dichalcogenides (TMDs) [4], hexagonal boron nitride (h-BN) [5], metal nanomaterials [6], black phosphorus (BP) [7], and graphdiyne [8], have been obtained and investigated by fundamental studies in the fields of optoelectronics, catalysis, and energy storage [9 -14]. Organic 2DMs, such as organic small molecules, polymers, and organic-inorganic hybrid materials, are emerging material systems currently attracting increasing attention owing to their unique advantages of a wide diversity of organic substrates, easily tunable properties/ functionalities, and diversified syntheses at low cost and high efficiency [15][16][17][18][19][20][21][22][23]. Among the 2DMs, 2D conjugated polymers (2DCPs) with long-range periodic covalently bonded structures and fully-extended conjugations have received special attention from scientists working in different fields. The tunable bandgap and diversified topological structures by appropriate molecular design [24-28] endow 2DCPs, as a type of promising graphene analogue, with unique/tunable optoelectronic and spintronic properties, as well as promising applications in plastic optoelectronics and related functional devices/ circuits [29][30][31][32][33][34][35].For the above mentioned fundamental studies and device applications, the most crucial issue of 2DCPs is their quality, which includes molecular orders, 2D-conjugated structures that determine the energy bandgaps/alignments and functionality of materials, and material sizes.Thus far, the preparation of 2DCPs with the desired compositions, thicknesses, sizes, defects, crystal polymorphs, and surface properties is the core topic. Various synthetic processes based on both "top-down" and "bottom-up" strategies have been developed [2,17]. On-surface chemistry synthesis, a very important "bottom-up" strategy, was developed to overcome the limitations of uncontrollable polymer thickness, low yield, and low structural integrity [17,36,37]. On-surface chemistry, sometimes referred to as 2D chemistry, is the coupling of active molecules on a flat interface to directly provide ordered and expanded nanostructures to polymers (Fig. 1a). The interface provides a restricted system for the growth of precursors, which are capable of forming planar structures that cannot be accessed in a 3D reaction environment. Compared with classical solution-phase processes, another advantage of the surface method is the contribution of the related reaction conditions and potential surface interactions to the stabilization of highly active substances and intermediates. Moreover, on-surface chemistry synthesis is advantageous for directing the orientations of molecules to form ordered structures, and hence, it has been e...

Two-dimensional polymer nanosheets for efficient energy storage and conversion

“…Interface polymerization methods, especially liquid-liquid, gas-liquid and gas-solid interface synthesis, are currently the most common methods for the bottom-up synthesis of ultrathin 2D polymer materials with controllable thickness, ordered and planar nanostructures [28].…”

“…Since the gas-liquid interface can provide an atomically flat surface on a large scale, the gas-liquid interface is widely used as a "soft template" for synthesizing 2D polymer nanosheets [28,33]. Polarity differences on both sides of the gas-liquid interface can help control the orientation of distributed molecules, thereby precisely controlling the arrangement of monomer molecules.…”

Recent advances in n-type and ambipolar organic semiconductors and their multi-functional applications

“…For example, the expansion of a reaction direction from one dimension to the second or even the third dimension is helpful for realizing new functions in new material platforms. 68,[383][384][385][386][387][388] The non-traditional reaction types, such as topochemical polymerization in single crystals, bring new hope for achieving high performance due to the highly ordered conjugated polymers in the solid state. 12,[389][390][391][392][393] Benefiting from the development of organic synthesis, a range of n-type and ambipolar functional materials are significantly achieved by introducing electron deficient building blocks or electron withdrawing functional groups.…”

A two-dimensional polymer memristor based on conformational changes with tunable resistive switching behaviours

“…More importantly, 2D covalent polymers have the advantages of good chemical and thermal stability, intrinsic flexibility and selfsupporting, adjustable thickness, green and convenient synthesis methods, etc. [24][25][26][27][28][29][30] Therefore, 2D polymer films are ideal candidates for constructing high-performance devices.…”