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Download fileNanoscrolls Formed from Two-Dimensional Covalent Organic Frameworks
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posted on 2019-04-02, 00:00 authored by Haoyuan Li, Jean-Luc BrédasTwo-dimensional (2D)
covalent organic frameworks (COFs) represent
an emerging class of nanomaterials with building blocks precisely
connected in-plane through covalent bonds. Gaining insights into their
structure and stabilities is critical to both their preparation and
applications. Here, via atomistic molecular mechanics simulations
and free-energy calculations, we investigate 2D COFs both under vacuum
conditions and in solution, taking representative boronate ester-based
and imine-based COFs as examples. Rather than remaining flat, single-layer
2D COF sheets with at least their length larger than ∼15–∼20
nm are found to preferably form nanoscrolls. These nanoscrolls display
a finite number of configurations and represent open structures due
to the large pores present in the 2D sheets; this feature distinguishes
them from nanoscrolls formed by dense 2D materials such as graphene.
Density functional theory calculations indicate that the intrasheet
interactions in the nanoscrolls make their optical and electrical
properties different from those of stand-alone sheets. The formation
of such scroll-like structures can pave the way to extended spiral
growth of 2D polymer networks and porous nanotubes.
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nanoscrolls displaybuilding blocksform nanoscrollsfree-energy calculationsspiral growth2 D polymer networksrepresentative boronate ester-basedmechanics simulationscovalent bondsimine-based COFs2 D sheets2 D COFstheory calculationsscroll-like structuressingle-layer 2 D COF sheets2 D materialsintrasheet interactionsvacuum conditions