Engineered 2D Polymers: Current Status and Future Trend

Abstract

Extending the concept of synthesizing 2 d polymer sheets has been explored in this mini review to highlight about the future potentials inherent with this important class of engineered materials. The discovery of graphene (i.e. mechanically and chemically robust highly crystalline nano sheets with extremely high charge carrier mobility) not only dispelled the thermodynamic instability of 2D materials but also established it as a material for ultrafast, and low power nanoelectronic devices besides motivating to look for other 2D materials to get rid of the zero band gap limitation of graphene causing poor 'on/off ' ratio for switching applications. IntroductionIn this search for the alternatives, surface-mediated growth of molecular assemblies on metal substrates using planar aromatic molecular building blocks was considered with conjugated backbones that were suitable for directional inter-molecular coupling leading to 1/2-D covalent and no covalent assemblies with precursor dependent forms and functions where relative strength and directionality of the intermolecular interactions were found to control the resultant molecular architectures facilitated by host-guest-networks, or growth templates.These nanostructures could be made to possess high charge carrier mobilities due to strong intermolecular coupling during their on-surface polymerization resulting in surface-confined 2D nanosheets. In this context, the organic macromolecules with programmable structure, composition, and functionalities became handy for their uses in (opto) electronic devices. Additionally, designing atomically precise pores would make them useful in membranes or sensors as shown in poly (paraphenylene) or graphene [1] nano ribbons. However, it would be essential to improve the quality of highly defective 2DPs that were synthesized initially lacking long-range orders by initiating polymerization on metal surfaces as template, wherefore different substrate materials, coupling reactions, and reaction parameters are possible to control the quality covalent networks better [2].Compared to a linear chain of polymer with each monomer linked to two neighbors in 1D-architecture, a two-dimensional polymer sheet (2DPS) contains covalently bonded molecular building blocks extending in 2D [3,4]. Preparation of mono/fewlayer of materials from natural and synthetic lamellar crystals exfoliated into nanosheets (as in case of graphene) is known to face problems in their synthesis, and production although characteristic (opto) electronic properties of their mono/few layered structures have been found possessing novel applications. Given the progress made in synthesizing these engineered 2DP sheets from available starting materials, the future prospects appear bright once larger sheets are produced with added functionalities incorporated on one/both sides. Enlarging the types of monomers involved in preparing 2DP sheets through different polymerization routes would certainly broaden the range of resultant engineered materials. Having overcome the c...