Over the past two decades, the charge carrier mobility of πconjugated polymers has vastly improved. This has been mostly achieved by increasing the π−π stacking ability of the polymers through advanced molecular design, thereby improving "interchain" charge carrier transport. However, the rational design of π-conjugated polymers for improving "intrachain" charge carrier transport along the backbone still remains a formidable challenge. Here, we show the synthesis of a new π-conjugated polymer based on a quinoidal bithiophene moiety (PSP4T), which interestingly, was found to have significantly extended π-electron delocalization along the backbone compared to its isomer (PBTD4T), although these polymers have an identical basic structure. Importantly, despite the similar π−π stacking structure, PSP4T demonstrated transistor mobilities of around 1−2.5 cm 2 V −1 s −1 that are 1−2 orders of magnitude higher than that of PBTD4T. On the basis of further investigations of energetic disorder and theoretical simulations, the higher mobility in PSP4T than in PBTD4T is most likely attributed to the remarkably higher intrachain charge carrier transport, which originates in the highly extended π-electron delocalization. We believe that our study can provide new guidelines for the design of πconjugated polymers with high intrachain charge carrier transport.

Development of n-type semiconducting polymers is essential for organic electronic devices. In this work, we synthesize a new strong acceptor unit by converting the fluorine groups on the naphthobisthiadiazole (NTz) moiety into cyano groups via a nucleophilic aromatic substitution reaction. As a result, the p-type character observed for polymers based on NTz and difluorinated NTz is switched into an ambipolar and/or n-type character in polymers based on dicyano NTz because of the significantly improved electron affinity and thus lowered lowest unoccupied molecular orbital levels. Interestingly, although the cyano groups cause an unfavorable sterical twist in the backbone, the polymers show high electron mobilities in organic field-effect transistors. We highlight that the dicyano NTz-based polymers form a high crystalline structure similar to the noncyano NTz-based polymers and that there seems to be short contacts between the cyano group and the NTz core in the adjacent polymer chain. These structural features would account for the high mobilities despite the backbone twisting. We propose that the introduction of cyano groups into a large π-system with an electron-poor nature is crucial for the development of n-type semiconducting polymers.

The effects of temperature and dwell time on the low-cycle fatigue life of Ag-epoxy based conductive adhesive have been investigated by using a micro-joint specimen. The low cycle fatigue life of the conductive adhesive increases when test temperature is elevated beyond the glass transition point. On the other hand, the dwell time at 398 K reduces the fatigue life, which, however, is increased by the dwell time at 348 K. The cross-sectional image suggests the embrittlement of epoxy resin during the dwell time at 398 K, which reduces the fatigue endurance of the conductive adhesive. In contrast, some kind of recovery effects exists during dwell time near the glass transition temperature, which improves the fatigue life.