Selvaraj Pravinraj, Li Po-Yin, Antony Mareena, Wang Yu-Wu, Chou Jyh-Pin, Chen Zhi-Hao, Hsu Che-Ju, Huang Chi-Yen
Opt Express. 2022 Mar 14;30(6):9521-9533. doi: 10.1364/OE.454130.
Liquid crystals (LCs) have been a vital component of modern communication and photonic technologies. However, traditional LC alignment on polyimide (PI) requires mechanically rubbing treatment to control LC orientation, suffering from dust particles, surface damage, and electrostatic charges. In this paper, LC alignment on organic single-crystal rubrene (SCR) has been studied and used to fabricate rubbing-free LC devices. A rubrene/toluene solution is spin-coated on the indium-tin-oxide (ITO) substrate and transformed thereafter to the orthorhombic SCR after annealing. Experimental result reveals that SCR-based LC cell has a homogeneous alignment geometry, the pretilt angle of LCs is low and the orientation of LCs is determined with capillary filling action of LCs. LC alignment on SCR performs a wider thermal tolerance than that on PI by virtue of the strong anchoring nature of LCs on SCR due to van der Waals and π-π electron stacking interactions between the rubrene and LCs. SCR-based LC cell performs a lower operation voltage, faster response time, and higher voltage holding ratio than the traditional PI-based LC cell. Organic SCR enables to play a role as weakly conductive alignment layer without rubbing treatment and offers versatile function to develop novel LC devices.
液晶（LCs）一直是现代通信和光子技术的重要组成部分。然而，传统的聚酰亚胺（PI）上的液晶取向需要机械摩擦处理来控制液晶取向，存在灰尘颗粒、表面损伤和静电电荷等问题。本文研究了有机单晶红荧烯（SCR）上的液晶取向，并将其用于制造无摩擦液晶器件。将红荧烯/甲苯溶液旋涂在氧化铟锡（ITO）衬底上，退火后转变为正交晶系的SCR。实验结果表明，基于SCR的液晶盒具有均匀的取向几何结构，液晶的预倾角较低，液晶的取向由液晶的毛细管填充作用决定。由于红荧烯与液晶之间的范德华力和π-π电子堆积相互作用，使得液晶在SCR上的取向比在PI上具有更宽的热耐受性。基于SCR的液晶盒比传统的基于PI的液晶盒具有更低的工作电压、更快的响应时间和更高的电压保持率。有机SCR能够在不进行摩擦处理的情况下作为弱导电取向层发挥作用，并为开发新型液晶器件提供多种功能。
