Conjugated polymers have been used for various optoelectronic applications, such as organic solar cells, thin film transistors, and light emitting diodes. Their optical and electronic properties, such as absorption, emission, and conductivity, are highly anisotropic due to the 1-dimensional <i>p</i>-orbital overlap along the conjugated polymer backbone. Therefore, unless conjugated polymers are assembled and aligned with a well-defined structure, their optical and electronic properties cannot be fully realized in their device applications. In reality, however, the directed assembly and particularly macroscopic alignment of CPs is a challenging task. Recently, our group investigated molecular design for directed alignment of CPs, and realized anisotropic optoelectronic properties from aligned CP films. When CPs satisfied three identified design rules; (1) concentration-induced planarization unit, and (2) bulky side chains linked to (3) a tetrahedral carbon, CP chains are readily aligned to the direction of flow field and exhibit a high dichroic ratio. The developed molecular design principle and application of lyotropic liquid crystalline conjugated polymers (LC CPs) having directed self-assembly and alignment feature will be discussed. Thin film transistors built on highly aligned such CP films showed more than three orders of magnitude faster carrier mobility along the CP alignment direction than the perpendicular direction. The established molecular design principle for directed alignment of CPs is readily applicable to many useful CP developments for various optoelectronic devices and to achieve the full realization of the anisotropic properties of CPs in devices such as photovoltaic cells.

Lyotropic liquid crystalline conjugated polymers with directed self-assembly and alignment capability for plastic electronics

256th National Meeting (2018)

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