Two molecular disks 1 and 2 composed of a central pyrene core, four oligothiopenes, and peripheral alkyl chains were synthesized and characterized with respect to optical and redox properties in solution and in solid films. It was found that the lowest unoccupied molecular orbital (LUMO) energy levels of 1 and 2 were ideal for achieving efficient electron transfer to fullerene derivatives PC₆₀BM and PC₇₀BM, and that 1 and 2 can function as electron donor components in solution-processed bulk-heterojunction (BHJ) solar cells. Disk-shaped molecules 1 and 2 organized ordered structures through intermolecular π-π interactions as monitored by temperature-controlled polarized optical microscope (TPOM), differential scanning calorimetry (DSC), and powder X-ray diffraction (XRD). Solution-processed BHJ solar cells using 1 or 2 as electron donor materials and fullerene derivatives as acceptor materials were fabricated and investigated. The oligothiophene lengths were reflected in the performance characteristics of solar cell devices fabricated using disk-shaped donors 1 and 2. Power conversion efficiency (PCE) of 2.6% was achieved for small-molecule BHJ solar cells containing self-organized crystals of 2 in the active layer under one sun condition.
We demonstrate that air-treated conjugated polymer diodes under photoexcitation give rise to a transient current exceeding a steady-state photocurrent by electron-spin resonance (ESR). The current induced by ESR is shown to exhibit a spiked time response for modulation of the resonance condition. The nature of the spike current is demonstrated to be a displacement current, which suggests that the spin transitions can change the film permittivity. This system has applications as devices enabling direct control of diode current by spin manipulation.
This study investigated the psychological conditions of Chinese international students in Japan during the COVID-19 pandemic, and the association between different forms of social capital and psychological outcomes (i.e., worries about being infected, subjective wellbeing, loneliness, and psychological coping responses). In our study, different forms of social capital refer to bonding social capital originating from host national and co-national networks, bridging social capital, and maintained social capital. A web-based cross-sectional survey was conducted in January 2021. Our results demonstrated that the effects of social capital on psychological conditions differed according to its form. Worries about being infected, loneliness, and negative coping had negative associations with bonding social capital originating from host national network, but no associations with bonding social capital originating from co-national network, bridging social capital, and maintained social capital. Subjective wellbeing had a positive relationship with social capital originating from host national network and bridging social capital. Positive coping was only significantly associated with bridging social capital. To help international students cope better with the pandemic, efforts are required to strengthen their host national networks and expand their weak-tie networks.
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