The energy of the lowest-lying triplet state (T1) relative to the ground and first-excited singlet states (S0, S1) plays a critical role in optical multiexcitonic processes of organic chromophores. Focusing on triplet–triplet annihilation (TTA) upconversion, the S0 to T1 energy gap, known as the triplet energy, is difficult to measure experimentally for most molecules of interest. Ab initio predictions can provide a useful alternative, however low-scaling electronic structure methods such as the Kohn–Sham and time-dependent variants of Density Functional Theory (DFT) rely heavily on the fraction of exact exchange chosen for a given functional, and tend to be unreliable when strong electronic correlation is present. Here, we use auxiliary-field quantum Monte Carlo (AFQMC), a scalable electronic structure method capable of accurately describing even strongly correlated molecules, to predict the triplet energies for a series of candidate annihilators for TTA upconversion, including 9,10 substituted anthracenes and substituted benzothiadiazole (BTD) and benzoselenodiazole (BSeD) compounds. We compare our results to predictions from a number of commonly used DFT functionals, as well as DLPNO-CCSD(T₀), a localized approximation to coupled cluster with singles, doubles, and perturbative triples. Together with S1 estimates from absorption/emission spectra, which are well-reproduced by TD-DFT calculations employing the range-corrected hybrid functional CAM-B3LYP, we provide predictions regarding the thermodynamic feasibility of upconversion by requiring (a) the measured T1 of the sensitizer exceeds that of the calculated T1 of the candidate annihilator, and (b) twice the T1 of the annihilator exceeds its S1 energetic value. We demonstrate a successful example of in silico discovery of a novel annihilator, phenyl-substituted BTD, and present experimental validation via low temperature phosphorescence and the presence of upconverted blue light emission when coupled to a platinum octaethylporphyrin (PtOEP) sensitizer. The BTD framework thus represents a new class of annihilators for TTA upconversion. Its chemical functionalization, guided by the computational tools utilized herein, provides a promising route towards high energy (violet to near-UV) emission.

中文翻译：

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通过辅助场量子蒙特卡罗对三重态-三重态湮没上转换的湮没物进行计算机预测

最低三重态 (T1) 相对于基态和第一激发单重态 (S0, S1) 的能量在有机发色团的光学多激子过程中起关键作用。专注于三重态-三重态湮没 (TTA) 上转换，对于大多数感兴趣的分子，S0 到 T1 的能隙（称为三重态能量）很难通过实验测量。从头算预测可以提供一个有用的替代方案，但是低尺度电子结构方法，例如 Kohn-Sham 和密度泛函理论 (DFT) 的时间相关变体，在很大程度上依赖于为给定泛函选择的精确交换分数，并且往往是当存在强电子相关性时不可靠。在这里，我们使用辅助场量子蒙特卡罗 (AFQMC)，一种能够准确描述强相关分子的可扩展电子结构方法，来预测一系列用于 TTA 上转换的候选湮灭剂的三重态能量，包括 9,10 取代的蒽和取代的苯并噻二唑（BTD）和苯并硒二唑（BSeD）化合物。我们将我们的结果与一些常用的 DFT 泛函以及 DLPNO-CCSD(T ₀)，一个局部近似耦合集群与单，双，和微扰三元组。连同来自吸收/发射光谱的 S1 估计，这些估计通过使用范围校正的混合功能 CAM-B3LYP 的 TD-DFT 计算很好地再现，我们通过要求 (a) 测量的 T1 来提供关于上转换的热力学可行性的预测敏化剂超过了候选歼灭者的计算 T1，并且（b）歼灭者的 T1 的两倍超过了其 S1 能量值。我们展示了一个成功的例子，在计算机上发现了一种新型湮没剂，苯基取代的 BTD，并通过以下方式进行了实验验证当与铂八乙基卟啉 (PtOEP) 敏化剂偶联时，低温磷光和上转换蓝光发射的存在。因此，BTD 框架代表了一类新的用于 TTA 上转换的歼灭剂。在本文使用的计算工具的指导下，其化学功能化为高能（紫色到近紫外）发射提供了一条有希望的途径。