materials Article The Inﬂuence of Disorder in the Synthesis, Characterization and Applications of a Modiﬁable Two-Dimensional Covalent Organic Framework Jordan Brophy 1 , Kyle Summerﬁeld 2 , Jiashi Yin 3 , Jon Kephart 1 , Joshua T. Stecher 1 , Jeramie Adams 4 , Takashi Yanase 5 , Jason Brant 1 , Katie Dongmei Li-Oakey 3 , John O. Hoberg 1, * and Bruce A. Parkinson 1,2, *   Citation: Brophy, J.; Summerﬁeld, K.; Yin, J.; Kephart, J.; Stecher, J.T.; Adams, J.; Yanase, T.; Brant, J.; Li-Oakey, K.D.; Hoberg, J.O.; Parkinson, B.A.et al. The Inﬂuence of Disorder in the Synthesis, Characterization and Applications of a Modiﬁable Two-Dimensional Covalent Organic Framework. Materials 2021, 14, 71. https:// doi.org/10.3390/ma14010071 Received: 5 November 2020 Accepted: 22 December 2020 Published: 25 December 2020 Publisher’s Note: MDPI stays neu- tral with regard to jurisdictional claims in published maps and institutional afﬁliations. Copyright: © 2020 by the authors. Li- censee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/ licenses/by/4.0/). 1 Department of Chemistry, University of Wyoming, Laramie, WY 82071, USA; jordanfbrophy@gmail.com (J.B.); jkephart@uw.edu (J.K.); Joshua.stecher@gmail.com (J.T.S.); jbrant270@yahoo.com (J.B.) 2 School of Energy Resources, University of Wyoming, Laramie, WY 82071, USA; ksummerf@uwyo.edu 3 Department of Chemical Engineering, University of Wyoming, Laramie, WY 82071, USA; yinjiashi@gmail.com (J.Y.); dli1@uwyo.edu (K.D.L.-O.) 4 Western Research Institute, University of Wyoming, Laramie, WY 82071, USA; Jeramie.adams@uwyo.edu 5 Division ofApplied Chemistry, Hokkaido University, Sapporo 060-0808, Japan; yanase42@eng.hokudai.ac.jp * Correspondence: hoberg@uwyo.edu (J.O.H.); bparkin1@uwyo.edu (B.A.P.) Abstract: Two-dimensional covalent organic frameworks (2D-COFs) have been of increasing inter- est in the past decade due to their porous structures that ideally can be highly ordered. One of the most common routes to these polymers relies on Schiff-base chemistry, i.e., the condensation reaction between a carbonyl and an amine. In this report, we elaborate on the condensation of 3,6-dibromobenzene-1,2,4,5-tetraamine with hexaketocyclohexane (HKH) and the subsequent car- bonylation of the resulting COF, along with the possibility that the condensation reaction on HKH can result in a trans conﬁguration resulting in the formation of a disordered 2D-COF. This strategy enables modiﬁcation of COFs via bromine substitution reactions to place functional groups within the pores of the materials. Ion-sieving measurements using membranes from this COF, reaction of small molecules with unreacted keto groups along with modeling studies indicate disorder in the COF polymerization process. We also present a Monte Carlo simulation that demonstrates the inﬂuence of even small amounts of disorder upon both the 2D and 3D structure of the resulting COF. Keywords: nanoporous covalent organic frameworks; carbonylation; ion sieving; disorder; carboxylated pores 1. Introduction Two-dimensional covalent organic frameworks (2D-COFs) are an emerging class of polymeric materials due to their expansive range of desirable properties [1–4]. 2D-COFs have regular porous structures that can be designed by the choice of monomers used in the polymerization reaction [2,5–7]. The bottom-up approach used in the synthesis of 2D-COFs relies on the extensive tools of synthetic organic chemistry that provide extraordinary control of both pore size, shape and spacing based on the choice of synthetic monomers [8]. Highly ordered materials can then be exploited in applications such as membrane sep- arations, optoelectronics and energy storage [9]. There have been a commonly used set of polymerization reactions employed to produce most 2D-COFs, most notably borate chemistry and condensation reactions between ketones and amines [10,11]. A particularly noteworthy example is nitrogen containing g-C 2 N, a hexagonal network of nitrogen-lined small pores produced by a condensation reaction between hexaketo cyclohexane (HKH) and benzene hexamine termed “holey graphene” [12]. This very stable material has a highly delocalized aromatic backbone and is reported to be highly ordered and have useful semiconductor properties based on high carrier mobilities measured in ﬁeld effect transistor (FET) devices. Although this material is very interesting, it is not amenable to modifying its Materials 2021, 14, 71. https://doi.org/10.3390/ma14010071 https://www.mdpi.com/journal/materials