Observing polymerization in 2D dynamic covalent polymers

Abstract

The quality of crystalline two-dimensional polymers (2DPs) 1-6 is intimately related to the elusive polymerization and crystallization processes. Understanding the mechanism of such processes at the (sub)molecular level is crucial to improve predictive synthesis and to tailor material properties for applications in catalysis 7-10 , and (opto)electronics 11, 12 , among others [13][14][15][16][17][18] . We characterize a model boroxine 2D dynamic covalent polymer, by using in situ scanning tunneling microscopy, to unveil both qualitative and quantitative details in the nucleation-elongation processes in real time and under ambient conditions. Sequential data analysis allows for the observation of the amorphous-to-crystalline transition, the timedependent evolution of nuclei, the existence of "nonclassical" crystallization pathways and importantly, the experimental determination of essential crystallization parameters including critical nucleus size, nucleation rate and growth rate with excellent accuracy. The experimental data has been further rationalized by atomistic computer models that altogether provide a detailed picture of the dynamic on-surface polymerization process. Furthermore, we show how two-dimensional crystal growth can be affected by abnormal grain growth (AGG). This finding provides support for the use of AGG -a typical phenomenon in metallic and ceramic systems -to convert a polycrystalline structure into a single crystal in organic and 2D material systems. Two-dimensional polymers (2DPs) -covalently linked networks of monomers in orthogonal directions-can be found as individual monolayers, as part of few-layer stacks, or as part of multilayered crystals, the latter known as 2D covalent organic frameworks (2D COFs). Over the past decade, research has focused on exploring efficient and controlled synthetic strategies to produce highly crystalline 2DPs [19][20][21][22][23][24][25][26] . Yet little is known about the mechanistic and kinetic aspects of the dynamic processes involving bond formation/breakage, nucleation,

Dynamically stable and amplified circularly polarized excimer emission regulated by solvation of chiral co-assembly process

“…7 and 11 ), which led to the decreased CPL signal. We proposed that crystallization process could control the critical nucleation size of the crystallites until spherulite growth tends to reach an equilibrium at the energetically favorable state and then causes the disappearance of the excimer 47 .

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Deprotonation-Induced Phase Transitions in the Self-Assembled Structure of Prochiral Carboxyl Derivatives

“…As shown in Figure S5, some incomplete hexamers are found at the edge of the β-phase, but there is no large area of the α-phase on the surface, which suggests the burst nucleation , of the β-phase. Recently, there has been some exciting progress in the kinetic processes of nucleation and phase transitions in 2D supramolecular structures. , Based on this progress, we suppose the deprotonation process of the carboxylic group on surfaces is irreversible and the formation of the β-phase is burst nucleation, and the nucleation of the β-phase and Ostwald ripening of the α-phase are limited to a relatively short period of time.…”

2D Conjugated Polymers: Exploiting Topological Properties for the Rational Design of Metal-Free Photocatalysts

“…Therefore, well-ordered 2D polymers have been successfully synthesized by manipulating the chemical equilibrium at the liquid/solid and vapor/solid interface, for example, in using boronic acids Schiff-base chemistry [101,102]. Recently, in-situ STM unveiled details of the nucleation process for the first time in real-time at the liquid/solid interface, which has enabled observation of the amorphous-to-crystalline transition, the time-dependent evolution of nuclei, and, importantly, the experimental determination of essential crystallization parameters with excellent accuracy [103]. In contrast, producing structural order using solvent-free onsurface synthesis procedures in ultra-high vacuum (UHV) is challenging and only a few strategies have been identified so far to fabricate micrometer-sized domains of 2D polymers.…”