Fully sp²‐Carbon‐Linked Crystalline Two‐Dimensional Conjugated Polymers: Insight into 2D Poly(phenylenecyanovinylene) Formation and its Optoelectronic Properties

Abstract

Cyano‐substituted polyphenylene vinylenes (PPVs) have been the focus of research for several decades owing to their interesting optoelectronic properties and potential applications in organic electronics. With the advent of organic two‐dimensional (2D) crystals, the question arose as to how the chemical and optoelectronic advantages of PPVs evolve in 2D compared with their linear counterparts. In this work, we present the efficient synthesis of two novel 2D fully sp2‐carbon‐linked crystalline PPVs and investigate the essentiality of inorganic bases for their catalytic formation. Notably, among all bases screened, cesium carbonate (Cs2CO3) plays a crucial role and enables reversibility in the first step with subsequent structure locking by formation of a C=C double bond to maintain crystallinity, which is supported by density functional theory (DFT) calculations. A quantifiable energy diagram of a “quasi‐reversible reaction” is proposed, which allows the identification of further suitable C−C bond formation reactions for 2D polymerizations. Moreover, the narrowing of the HOMO–LUMO gap is delineated by expanding the conjugation into two dimensions. To enable environmentally benign processing, the post‐modification of 2D PPVs is further performed, which renders stable dispersions in the aqueous phase.

Synthesis of Vinylene‐Linked Two‐Dimensional Conjugated Polymers via the Horner–Wadsworth–Emmons Reaction

“…[12] In particular, sp 2 -carbonlinked (or vinylene-linked) 2D CPs provide high chemical and thermal stabilities as well as complete p-conjugation over the whole 2D polymer framework, making these materials highly attractive for various applications, such as in optoelectronics, spintronics, and energy storage. [13][14][15] Thus far, only Knoevenagel [13][14][15]16] and other aldol-type condensation [17][18][19] reactions have been reported for the synthesis of crystalline vinylenelinked 2D CPs. However, Knoevenagel polycondensation provides cyano-vinylene-linked 2D CPs in which additional cyano-groups on the conjugated backbone cause structural twisting due to steric hindrance.…”

Thiophene‐Bridged Donor–Acceptor sp2‐Carbon‐Linked 2D Conjugated Polymers as Photocathodes for Water Reduction

“…[8,17,28] Recently, 2D sp 2 -carbon-linked (or vinylene-linked) conjugated polymers (2D CCPs) have attracted growing attention due to the extended π-conjugation over the whole 2D polymer framework as well as the high chemical stability against acids and bases, in contrast to imine-linked 2D COFs [9,17,19,20] However, most of the reported 2D CCPs are not suitable candidates for PEC applications due to the inefficient light harvesting and consequently large optical energy gaps in the range of 2.2-2.4 eV (Table S5, Supporting Information). [9,[21][22][23][24][25] One promising strategy to regulate the optoelectronic properties of 2D conjugated polymers is the incorporation of donor and acceptor (D-A) conjugated structures, [26] which can be beneficial for PEC applications.…”

All sp2 carbon covalent organic frameworks

“…Topology diagram: the scheme in which monomers are designed to possess specific geometries so that their connections enable the growth of extended polygonal architectures. hexagonal frameworks (Figure 1A) [13,18,21,[29][30][31][32][33][34][35]. The [C 4 + C 2 ] combination with a C 4 -symmetric knot and C 2 -symmetric linker generates tetragonal frameworks so that the polymer backbones extend along both the x and y directions (Figure 1B) [20,36].…”

“…Jiang and colleagues in 2016 reported a Knoevenagel reaction for the first time to synthesize sp 2 carbon COFs, including sp 2 c-COF, sp 2 c-COF-2, and sp 2 c-COF-3 (Figure 3A-C) by condensing TFPPy with BPDA, PBPDA, and TBPDA, respectively [12,14,15]. Later, condensation of TFPT, TCPB, and HFPTP with PDAN, TFPB, BPDA, PDAN, and BPDAN has been reported to produce TP-COF, 2D-CN-PPV-1, 2D-CN-PPV-1, 2D-CCP-1, and 2D-CCP-2, respectively (Figure 3D-H) [18,21,24].…”

“…Interestingly, Jiang and colleagues observed that 2D sp 2 carbon COFs are distinct from 1D sp 2 carbon polymers and graphene in terms of their π conjugation and polaron behavior [14]. This finding inspired the synthesis of a diversity of sp 2 carbon COFs with different building blocks and topologies, shaping a molecular platform for the exploration of sp 2 carbon materials [15][16][17][18][19][20][21][22][23][24][25].…”