Luminescent sp²-Carbon-Linked 2D Conjugated Polymers with High Photostability

Abstract

Luminescent organic materials with high photostability are essential in optoelectronics, sensor, and photocatalysis applications. However, small organic molecules are generally sensitive to UV irradiation, giving rise to chemical decompositions. In this work, we demonstrate two novel CN-substituted twodimensional sp 2 -carbon-linked conjugated polymers (2D CCPs) containing a chromophore triphenylene unit. The Knoevenagel polymerization between 2,3,6,7,10,11-hexakis(4-formylphenyl)triphenylene (HFPTP) and 1,4-phenylenediacetonitrile (PDAN) or 2,2′-(biphenyl-4,4′-diyl)diacetonitrile (BDAN), provides the crystalline 2D CCP-HFPTP-PDAN (2D CCP-1) and 2D CCP-HFPTP-BDAN (2D CCP-2) with dual pore structures, respectively. 2D CCP-1 and 2D CCP-2 exhibit the photoluminescence quantum yield (PLQY) up to 24.9 and 32.3%, which are the highest values among the reported 2D conjugated polymers and πconjugated 2D covalent organic frameworks. Furthermore, compared with the well-known emissive small molecule tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN), both 2D CCPs show superior photostability under UV irradiation for 2 h, profiting from the twisted and rigid structures of the CN-substituted vinylene linkages. The present work will trigger the further explorations of novel organic emitters embedded in 2D CCPs with high PLQY and photostability, which can be useful for optoelectronic devices.

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

“…In contrast, 2D CN COF‐B and 2D CCP‐Th did not show apparent fluorescence. The fluorescence quenching of 2D CN COF‐B can be attributed to the thermal dissipation due to the rotationally labile imine bonds, [ 40,41 ] while for 2D CCP‐Th, the intimate interaction between the donor and acceptor units can lead to nonradiative recombination processes. [ 42,43 ]…”

All sp2 carbon covalent organic frameworks

“…The dual-pore trigonal 2D CCP-1 (Figure 3G) and 2D CCP-2 (Figure 3H) emit at 507 and 500 nm, respectively [24]. The fluorescence quantum yields of 2D CCP-1 and 2D CCP-2 in the solid state are 24.9% and 32.3%, which are more than 60 times as high as that of the imine-linked analog 2D C=N COF-1 (0.4%).…”

“…Kagome COFs usually comprise two different types of pores, hexagonal mesopores and trigonal mesopores or micropores [17]. The [C 3 + C 2 ] diagram with a C 3 -symmetric knot but six reactive sites and a C 2 -symmetric linker allows the design of trigonal skeletons with two different pore sizes (Figure 1E) [19,24,37,38]. These topology diagrams constitute the chemical base for the design of 2D sp 2 carbon COFs.…”

“…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].…”