Fabricating ultrathin two-dimensional (2D) covalent organic framework (COF) nanosheets (NSs) in large scale and high yield still remains a great challenge. This limits the exploration of the unique functionalities and wide range of application potentials of such materials. Herein, we develop a scalable general bottom-up approach to facilely synthesize ultrathin (<2.1 nm) imine-based 2D COF NSs (including COF-366 NSs, COF-367 NSs, COF-367-Co NSs, TAPB-PDA COF NSs, and TAPB-BPDA COF NSs) in large scale (>100 mg) and high yield (>55%), via an imine-exchange synthesis strategy through adding large excess amounts of 2,4,6-trimethylbenzaldehyde into the reaction system under solvothermal conditions. Impressively, visualization of the periodic pore lattice for COF-367 NSs by a scanning tunneling microscope (STM) clearly discloses the ultrathin 2D COF nature. In particular, the ultrathin COF-367-Co NSs isolated are subject to the heterogeneous photocatalyst for CO2-to-CO conversion, showing excellent efficiency with a CO production rate as high as 10 162 μmol g–1 h–1 and a selectivity of ca. 78% in aqueous media under visible-light irradiation, far superior to corresponding bulk materials and comparable with the thus far reported state-of-the-art visible-light driven heterocatalysts.

Poly(4,8-dialkyl-2,6-bis(3-alkylthiophen-2-yl)benzo[1,2-b:4,5-b‘]dithiophene) 1 represents a new class of polymer semiconductors which self-assemble into higher structural orders without thermal annealing and provide excellent field-effect transistor performance with mobility up to 0.25 cm2 V-1 s-1 when used as a solution-processed thin-film semiconductor in thin-film transistors.

Printed organic thin-film transistors (OTFTs) have received great interests as potentially low-cost alternative to silicon technology for application in large-area, flexible, and ultra-low-cost electronics. One of the critical materials for TFTs is semiconductor, which has a dominant impact on the transistor properties. We review here the structural studies and design of thiophene-based polymer semiconductors with respect to solution processability, ambient stability, molecular self-organization, and field-effect transistor properties for OTFT applications. We show that through judicial monomer design, delicately controlled pi-conjugation, and strategically positioned pendant side-chain distribution, novel solution-processable thiophene polymer semiconductors with excellent self-organization ability to form extended lamellar pi-stacking orders can be developed. OTFTs using semiconductors of this nature processed in ambient conditions have provided excellent field-effect transistor properties.

[1] represent a promising class of polymer semiconductors for solution-processed thin-film transistors (TFTs), [2][3][4][5][6] an emerging technology that has received phenomenal interest as a lowcost alternative to silicon-based TFTs to enable ubiquitous, large-area, flexible electronics. In general, low-cost TFT fabrication requires a noninert processing environment, which necessitates the semiconductors to possess a certain level of air stability, particularly resistance against photoinduced oxidative doping. From this perspective, several regioregular polythiophenes with improved air stability have been developed, [6][7][8] potentially enabling low-cost TFT manufacturing.The sensitivity of regioregular polythiophenes to photo-oxidative doping is a consequence of photoexcitation, leading to charge transfer to atmospheric oxygen and, hence, charge-carrier generation. [3,9] This results in increased semiconductor conductivity, and thus degraded semiconductor properties. This difficulty has recently been overcome by a simple structural design, schematically represented by structure A (Fig. 1). The effective p-conjugation length of the polythiophene system is curtailed by a conjugating moiety, M, suppressing its sensitivity by lowering its highest occupied molecular orbital (HOMO) level.[6] Thus, we observe that with a proper choice of M such as unsubstituted bithienylene as in poly(didodecylquarterthiophene) (PQT) 1, [6c] high-mobility TFTs can be fabricated under ambient conditions. Very recently, other members of this class have also been developed as functionally capable semiconductors. [7,8] Specifically, poly(2,5-bis(3-dedecyl-thiophen-2-yl)thieno[3,2-b]thiophene) was reported to give a mobility of 0.2-0.6 cm 2 V -1 s -1 , albeit under inert atmosphere.[10] This latest result has prompted us to report our independent study of another novel system, schematically described by structure B, in which the alkyl side chains are bound to M to optimize its processability, molecular organization, and electronic properties in the solid state. We show herein, through poly(2,5-bis(2-thienyl)-3,6-dialkylthieno[3,2-b]-thiophene), 2, that this class of polythiophenes affords high mobility at low processing temperatures under ambient conditions. The synthesis of poly(2,5-bis(2-thienyl)-3,6-dipentadecylthieno[3,2-b]thiophene) 2 is described in Scheme 1. 2,5-Dibromo-3,6-dipentadecylthieno[3,2-b]thiophene 3 was prepared from 3,4-dibromothiophene in good yields. Stille coupling of 3 with 2-tributylstannylthiophene, followed by bromination, gave 2,5-bis(2-bromo-thienyl)-3,6-dipentadecylthieno[3,2-b]thiophene 5 in ca. 60 % yield.[11] Subsequent dehalogenative coupling polymerization was carried out in the presence of a slight excess of Ni(COD) 2 (COD: 1,5-cyclooctadiene) and a catalytic amount of 2,2′-dipyridil in refluxing toluene. Soxhlet extraction of the crude product to remove oligomeric materials yielded 2 as a dark red solid in 92 % yield. High-temperature gel permeation chromatography (GPC) analysis gave a number-average...