[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...

Organic solids and polymers that absorb in the near-infrared (NIR) region (1000-2000 nm) represent a class of emerging materials and show a great potential for use in photonics and telecommunications. The radical anions of stacked aromatic imides, fused phorphyrin arrays, polythiophenes, sandwich-type lanthanide bisphthalocyanines, semiquinones, and mixed-valence dinuclear metal complexes are a few known examples of NIR-absorbing organic materials. Most of these NIR-absorbing materials are also electrochemically active or electrochromic (EC). This brief review covers several types of NIR-absorbing organic materials and discusses their potentials for applications in EC variable optical attenuators (VOAs).

The synthesis and near-infrared electrochromic properties of pentacenediquinone-containing monomers and polymers are reported. The electroactive pentacenediquinone units were incorporated into poly(aryl ether)s in varying degrees by copolymerization. The polymers possessed good thermal stabilities and high glass transition temperatures, and could undergo two reversible steps of electrochemical reduction. Near-infrared electrochromic properties of pentacenediquinone-containing poly(aryl ether)s were studied by spectroelectrochemical analysis, which showed that the radical anions possess intense near-infrared absorption with λ max values between 1331 and 1430 nm, while the dianions also exhibit absorption between 880 and 965 nm. The reduced polymer film displayed intense and broad near-infrared absorption, which was surprisingly stable in air over a long period. The neutral and reduced polymers had electrical conductivity of 1 × 10 -6 and 3 × 10 -3 S/cm, respectively.

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