盘状液晶有序结构构筑与性能关系

Discotic liquid crystals(DLCs) are promising candidates for use as charge-transport materials in organic photovoltaics (OPVs) and thin film transistors (TFTs) due to their comparatively high charge carrier mobility and large exciton diffusion length. In order to realize high charge carrier mobility of DLCs, the essential questions are as follows: how to realize the room-temperature liquid crystal character of DLCs, how to self-assemble into ordered one-dimensional columnar stacks and how to realize the orientation of columnar stacks. On account of these key issues, this research project will focus on the following aspects: (1) room-temperature liquid crystal character and liquid crystal phase stability for n-type DLC molecules: obtaining LCs and preserving columnar hexagonal packing in a broad temperature domain by variations of the properties of flexible side chains, which include length, number, branched structures, asymmetry, etc. (2) self-assembly dynamics, ordered columnar stacks and oriented alignment for n-type DLC molecules: achieving DLCs ordered columnar packing by control of non-equilibrium force; providing much more time for self-assembly of discotic molecules; studying the ability of discotic liquid crystals to self-heal stacking defects due to their liquid-like character; realizing long-range ordered stacks and face-on orientation of discotic molecules by substrate induction and solution gradient method. (3) establish the relationship between DLC molecular structure, thin film morphology and performance of organic photovoltaic devices.

盘状液晶分子由于具有较高的载流子迁移率和激子扩散长度，在有机光伏电池以及薄膜晶体管方面具有潜在的应用前景。其核心问题是如何实现盘状液晶的室温液晶性、一维有序柱状堆积以及柱状相的取向排列，从而实现较高的载流子迁移率。针对这些关键问题，本项目将重点研究：（1）盘状液晶分子的室温液晶性和液晶相稳定性：通过调控柔性侧链的长度和数目、分支结构、非对称烷基侧链等使得盘状分子具有宽的液晶性温度区间而且在较宽的温度区间内均以六方柱状液晶相的形式存在。（2）盘状液晶分子的动力学与有序柱状堆积和取向排列：通过调控内核、侧链相互作用和非平衡力的作用调控盘状液晶有序柱状堆积。使盘状分子具有更长的时间进行自组装。研究其在液晶态下的流动性对分子堆叠缺陷的修复作用。通过基底诱导和溶液梯度等成膜方式，实现长程有序堆叠形成face-on取向排列。（3）建立盘状液晶分子分子结构、薄膜形貌与载流子迁移率之间的关系。

盘状液晶分子等具有共轭结构的小分子其合成简单、结构明确及纯度较高，且具有较高的载流子迁移率和激子扩散长度，在有机光伏电池以及薄膜晶体管方面具有潜在的应用前景。分子凝聚态结构决定其性能，然而由于共轭小分子扩散能力强，纯相薄膜及相应共混体系中聚集行为可控性差。因此如何在较低的温度区间加工使其具有一维有序柱状堆积以及柱状相的取向排列；如何调控共轭小分子结晶动力学及热力学稳定态，使其聚集行为可控；及如何实现共混体系中共轭小分子的相区尺寸可控等是目前亟需解决的关键问题。鉴于此，本项目在调控分子有序排列、聚集形态及相应共混体系相分离行为等方面做了初步探讨，取得如下结论：（1）通过调节分子间烷基侧链间作用力与π-π作用力竞争关系及引入电荷转移作用调节液晶温度区间的方法降低盘状液晶分子液晶温度区间。（2）通过调控分子内核尺寸、溶剂性质调节、后退火处理及高分子添加剂等手段实现分子间作用力的调节实现分子长程有序排列，利用互补性的盘状分子构筑具有双极传输性质的共晶薄膜。（3）通过调节溶剂分子、给体分子以及受体分子间的相互作用，实现了共混体系中相区尺寸、共混相含量的调控及互穿网络结构的构筑。