Opto-Electronic Materials Section, Department of Chemical Engineering, Faculty of Applied Sciences, Delft University of Technology, Van der Maasweg 9, 2629 HS Delft, The Netherlands.
J Chem Phys. 2019 Sep 7;151(9):094301. doi: 10.1063/1.5110306.
Perylene diimides (PDIs) are attractive chromophores that exhibit singlet exciton fission (SF) and have several advantages over traditional SF molecules such as tetracene and pentacene; however, their photophysical properties relating to SF have received only limited attention. In this study, we explore how introduction of bulky bromine atoms in the so-called bay-area PDIs, resulting in a nonplanar structure, affects the solid-state packing and efficiency of singlet fission. We found that changes in the molecular packing have a strong effect on the temperature dependent photoluminescence, expressed as an activation energy. These effects are explained in terms of excimer formation for PDIs without bay-area substitution, which competes with singlet fission. Introduction of bromine atoms in the bay-positions strongly disrupts the solid-state packing leading to strongly reduced excitonic interactions. Surprisingly, these relatively amorphous materials with weak electronic coupling exhibit stronger formation of triplet excited states by SF because the competing excimer formation is suppressed here.
并五苯二酰亚胺（PDIs）是一种吸引人的发色团，具有单重态激子裂变（SF）的特性，并且与苝和薁等传统 SF 分子相比具有多个优势；然而，与 SF 相关的其光物理性质仅受到有限的关注。在这项研究中，我们探讨了在所谓的海湾区域 PDIs 中引入大体积的溴原子导致非平面结构，如何影响固态堆积和单重态裂变的效率。我们发现，分子堆积的变化对温度依赖性的光致发光有很强的影响，表现为激活能。这些效应可以用没有海湾区域取代的 PDIs 中激子的形成来解释，这与单重态裂变竞争。在海湾位置引入溴原子强烈地破坏了固态堆积，导致激子相互作用大大减弱。令人惊讶的是，这些相对无定形的材料具有较弱的电子耦合，由于此处抑制了竞争的激子形成，因此通过 SF 形成更强的三重态激发态。
