Large Exciton Diffusion Coefficients in Two Dimensional Covalent Or-ganic Frameworks with Different Domain Sizes Revealed by Ultrafast Exciton Dynamics,Journal of the American Chemical Society

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Large Exciton Diffusion Coefficients in Two Dimensional Covalent Or-ganic Frameworks with Different Domain Sizes Revealed by Ultrafast Exciton Dynamics
Journal of the American Chemical Society ( IF 14.4 ) Pub Date : 2020-07-11 , DOI: 10.1021/jacs.0c05404
Nathan C Flanders ₁ , Matthew S Kirschner ₁ , Pyosang Kim ₁ , Thomas J Fauvell _{1,

2} , Austin M Evans ₁ , Waleed Helweh ₁ , Austin P Spencer ₁ , Richard D Schaller _{1,

3} , William R Dichtel ₁ , Lin X Chen _{1,

2}

Affiliation

Large singlet exciton diffusion lengths are a hallmark of high performance in organic based devices such as photovoltaics, chemical sensors, and photodetectors. In this study, exciton dynamics of a two-dimensional covalent organic framework, COF-5, is investigated using ultrafast spectroscopic techniques. Following photoexcitation, the COF-5 exciton decays via three pathways: 1) excimer formation (4 ± 2 ps), 2) excimer relaxation (160 ± 40 ps), and 3) excimer decay (>3 ns). Excita-tion fluence-dependent transient absorption studies suggest that COF-5 has a relatively large diffusion coefficient (0.08 cm2/s). Furthermore, exciton-exciton annihilation processes are characterized as a function of COF-5 crystallite domain size in four different samples, which reveal domain-size dependent exciton diffusion kinetics. These results reveal that exciton diffusion in COF-5 is constrained by its crystalline domain size. These insights indicate the outstanding promise of delocalized excitonic processes available in 2D COFs, which motivate their continued design and implementation into optoelectronic devices.

中文翻译：

超快激子动力学揭示了具有不同域尺寸的二维共价有机框架中的大激子扩散系数

大单线态激子扩散长度是有机器件（如光伏器件、化学传感器和光电探测器）中高性能的标志。在这项研究中，使用超快光谱技术研究了二维共价有机骨架 COF-5 的激子动力学。光激发后，COF-5 激子通过三种途径衰减：1) 准分子形成 (4 ± 2 ps)，2) 准分子弛豫 (160 ± 40 ps)，和 3) 准分子衰减 (> 3 ns)。依赖于激发通量的瞬态吸收研究表明 COF-5 具有相对较大的扩散系数 (0.08 cm2/s)。此外，激子-激子湮灭过程被表征为四个不同样品中 COF-5 微晶域尺寸的函数，这揭示了域尺寸依赖的激子扩散动力学。这些结果表明，COF-5 中的激子扩散受到其晶畴尺寸的限制。这些见解表明 2D COF 中可用的离域激子过程的杰出前景，这促使它们继续设计和实施到光电器件中。

更新日期：2020-07-11

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