Twisted tetrathiafulvalene crystals
Twisted tetrathiafulvalene crystals
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DOI：
10.1039/d2me00010e
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发表时间：
2022-02-16
影响因子：
3.6
通讯作者：
Lee, Stephanie S.
中科院分区：
文献类型：
--
作者：
Yang, Yongfan;Zong, Kai;Lee, Stephanie S.
光学活性光电材料在许多应用中引起了极大的兴趣，包括手性传感和圆偏振光发射。传统上，此类应用是通过设计手性有机半导体和导体的合成策略来实现的。在这里，中心对称四硫富瓦烯（TTF）晶体通过晶体扭曲在介观尺度上呈现手性。在熔体结晶过程中，观察到螺旋 TTF 纤维从成核中心以球晶形式径向向外生长，并围绕生长方向一致扭转。由于分子晶体表现出与取向相关的折射率，因此当在交叉偏振器之间成像时，在球晶内观察到与连续旋转晶体取向相关的周期性同心带。在某些条件下，观察到伴随的晶体扭曲和弯曲，导致不规则晶体光学行为。在不同球晶带上收集的 X 射线衍射测量表明，直 TTF 晶体和扭曲 TTF 晶体之间的分子堆积没有差异，正如对 20-200 μm 之间的微观扭曲节距所预期的那样。然而，穆勒矩阵成像显示，扭曲晶体中左旋或右旋圆偏振光的优先吸收和折射取决于生长方向的顺时针或逆时针扭曲方向。此外，对于沉积在有机场效应晶体管平台上的直型和扭曲型TTF晶体，测量到的空穴迁移率分别为2.0 +/- 0.9 x 10(-6) cm(2) V-1 s(-1)和1.9 +/- 0.8 x 10(-5) cm(2) V-1 s(-1)，表明晶体扭曲不会对这些系统中的电荷传输产生负面影响。
Optically-active optoelectronic materials are of great interest for many applications, including chiral sensing and circularly polarized light emission. Traditionally, such applications have been enabled by synthetic strategies to design chiral organic semiconductors and conductors. Here, centrosymmetric tetrathiafulvalene (TTF) crystals are rendered chiral on the mesoscale by crystal twisting. During crystallization from the melt, helicoidal TTF fibers were observed to grow radially outwards from a nucleation centre as spherulites, twisting in concert about the growth direction. Because molecular crystals exhibit orientation-dependent refractive indices, periodic concentric bands associated with continually rotating crystal orientations were observed within the spherulites when imaged between crossed polarizers. Under certain conditions, concomitant crystal twisting and bending was observed, resulting in anomolous crystal optical behavior. X-ray diffraction measurements collected on different spherulite bands indicated no difference in the molecular packing between straight and twisted TTF crystals, as expected for microscopic twisting pitches between 20-200 mu m. Mueller matrix imaging, however, revealed preferential absorption and refraction of left- or right-circularly polarized light in twisted crystals depending on the twist sense, either clockwise or counterclockwise, about the growth direction. Furthermore, hole mobilities of 2.0 +/- 0.9 x 10(-6) cm(2) V-1 s(-1) and 1.9 +/- 0.8 x 10(-5) cm(2) V-1 s(-1) were measured for straight and twisted TTF crystals deposited on organic field-effect transistor platforms, respectively, demonstrating that crystal twisting does not negatively impact charge transport in these systems.