SusChEM: Design Principles Inspired by Symmetry for Controlling Singlet Fission in Structurally Well-Defined Covalent Dimers

在化学系化学结构与动力学机制B项目资助的课题中，Niels H.科罗拉多大学博尔德分校化学和生物化学系的达姆劳尔和塔里克·萨马基亚正在合成含有两个发色团的新有机分子系统（即，分子中可以吸收光的部分），并使用光谱学来探索它们的光物理学。我们的目标是开发设计规则，如何安排的发色团控制激发态反应后可见光光激发。感兴趣的特定反应在某些下一代策略中是重要的，以通过限制通常在吸收更高能量的太阳光子时发生的废热产生来提高太阳能电池的效率。该提案建立了一个基础研究计划，学生将接触到合成，光谱学和电子结构理论应用的相当广泛的想法。与当地高中教师合作的一项具体推广工作是资助工作的一部分，旨在为科罗拉多高中科学项目提供复杂但负担得起的光谱工具和课程理念。单线态裂变是在某些有机材料中观察到的光物理现象，其中光吸收产生自旋允许的单线态激发态，然后非辐射地转换为一对三线态激发。如果这些三重态可以进一步转化为电荷载流子，那么与目前运行的设备相比，可以设想更有效地利用太阳光谱的设备场景。这项研究是基于这样的想法，即分子二聚体是单线态裂变的基本单元，它们可以提供一个平台，其中控制发色团的空间并置和共价相互作用的合成操作被要求影响关键的电子物理速率常数。正在测试的最重要的设计机会涉及二聚体点群对称性，以及它可以控制单重态裂变非绝热耦合量子力学描述中路径的干扰（建设性与破坏性）的想法。其他策略将要求取代基影响电荷转移态的相对能量。

In this project funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, Professors Niels H. Damrauer and Tarek Sammakia of the Department of Chemistry and Biochemistry at the University of Colorado Boulder are synthesizing new organic molecular systems that contain two chromophores (i.e., parts of the molecules that can absorb light) and using spectroscopy to explore their photophysics. The goal is to develop design rules for how the arrangement of the chromophores controls excited state reactivity following visible light photoexcitation. The particular reaction of interest is important in certain next-generation strategies to increase the efficiency of solar cells by limiting waste heat production that generally occurs when higher energy solar photons are absorbed. This proposal establishes a fundamental research program where students are exposed to a considerable breadth of ideas in synthesis, spectroscopy, and applications of electronic structure theory. A specific outreach effort in collaboration with local high school teachers is part of the funded work that aims to provide sophisticated but affordable spectroscopic tools and curriculum ideas to Colorado high school science programs. Singlet fission is a photophysical phenomenon observed in certain organic materials wherein light absorption produces a spin-allowed singlet excited state that then non-radiatively converts to a pair of triplet excitations. If these triplets can be further transformed to charge carriers, it is possible to envision device scenarios where the solar spectrum is more efficiently utilized compared to devices in operation today. This research is predicated on the idea that molecular dimers are the fundamental unit for singlet fission and that they can provide a platform wherein synthetic manipulations that control the spatial juxtaposition and covalent interaction of chromophores are called upon to affect key photophysical rate constants. The most important design opportunity that is being tested relates to dimer point group symmetry and the idea that it can control the interference (constructive vs. destructive) of pathways in the quantum mechanical description of diabatic coupling for singlet fission. Other strategies will call on substituents to affect the relative energy of charge transfer states.