CAS: Photocatalysis Without Metals: Design Rules for Organic Photoredox Chemistry

CAS：无金属光催化：有机光氧化还原化学的设计规则

• 批准号: 2102044
• 负责人: Shaama Sharada
• 金额: $ 30.62万
• 依托单位: University of Southern California
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2021
• 资助国家: 美国
• 起止时间: 2021-09-01 至 2024-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2102044&HistoricalAwards=false
• 关键词: CAS; Photocatalysis; Without; Metals; Design

With support from the Chemical Structure, Dynamics, and Mechanisms-A (CSDM-A) Program in the Division of Chemistry, Shaama M. Sharada and her group at the University of Southern California (USC) are using computational methods to study organic photoredox catalysts. There is growing need for strategies to mitigate the adverse impacts of climate change. Carbon capture and utilization offers means to trap and transform anthropogenic carbon dioxide (CO2) into useful fuels and chemicals. Harnessing sunlight to carry out CO2 conversion is essential because breaking the bonds in CO2 requires high energy input. Using organic light-activated molecules, or chromophores, as catalysts to facilitate this transformation lowers cost and toxicity concerns compared to traditional, heavy metal thermal catalysts. Developing a fundamental mechanistic picture of the photoredox catalytic cycle is an essential first step toward unlocking the potential of these materials. Dr. Sharada and her research team aim to use quantum chemistry methods and machine learning to generate mechanistic insights and catalyst design rules for CO2 conversion. The design rules are expected to have broader impact beyond carbon dioxide utilization as these catalysts find applications in organic synthesis, water-splitting, drug delivery, and biocides. Open-source modeling software used by the Sharada group for research can also serve as powerful visual learning aids for high school students. Since lasting impact can be achieved through partnership with teachers, summer externships are planned for teachers at the Hawthorne Math and Science Academy, to train them in the use of modeling methods and support the design of lesson plans for environmental sciences, chemistry, and biology classes.Photoredox catalytic cycles with organic chromophores are difficult to study using experiments alone owing to the generation of several radical intermediates, complex solvation effects, varied product distributions, and low catalyst turnover numbers. Despite methodological advances in the treatment of charge transfer processes, organic chromophore studies largely focus on optoelectronic applications while mechanistic studies of photoredox cycles remain limited. This work aims to pioneer the adaptation of a foundational principle in heterogeneous catalysis – the Sabatier principle – to photoredox systems and identify innate trade-offs that govern catalytic activity and turnover number (or resistance to degradation). The goal is to characterize exciplexes formed between the excited-state chromophore and electron donor prior to quenching and determine factors that favor complete quenching and charge separation vis-à-vis chromophore degradation via Birch reduction. To this end, multiple quantum chemistry methods are to be employed, including density functional theory (DFT), constrained DFT, time-dependent DFT, and energy decomposition analysis for ground, excited-state, and solvated systems. Factors that lower the likelihood of degradation will be juxtaposed with those that also enhance the rates of electron transfer to CO2 to identify trade-offs underlying these performance metrics. Characteristics of the photoredox system – solvent, electron donor, and chromophore properties – that lead to the desired balance between activity and degradation are expected to emerge. The computational work will be supported by experimental transient absorption spectroscopy studies by a collaborator at USC. Finally, these design rules will feed into machine learning methods to accelerate discovery, by rapidly searching the vast chemical space for chromophores that possess desired characteristics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.

在化学系化学结构、动力学和机理(CSDM-A)计划的支持下，南加州大学(USC)的Shaama M.Sharada和她的团队正在使用计算方法研究有机光氧化还原催化剂。人们越来越需要制定战略来减轻气候变化的不利影响。碳捕获和利用提供了捕获人为二氧化碳(CO2)并将其转化为有用燃料和化学品的方法。利用阳光进行二氧化碳转化是必不可少的，因为打破二氧化碳中的键需要高能量输入。与传统的重金属热催化剂相比，使用有机光活化分子或发色团作为催化剂来促进这种转化降低了成本和毒性。开发光氧化还原催化循环的基本机理图是释放这些材料潜力的必要的第一步。莎拉达博士和她的研究团队的目标是使用量子化学方法和机器学习来生成二氧化碳转化的机械洞察力和催化剂设计规则。随着这些催化剂在有机合成、水分解、药物输送和杀菌剂中的应用，设计规则预计将产生比二氧化碳利用更广泛的影响。Sharada团队用于研究的开源建模软件也可以作为高中生强大的可视化学习辅助工具。由于可以通过与教师的合作来实现持久的影响，因此计划为霍桑数学和科学学院的教师提供暑期外部培训，以培训他们使用建模方法，并支持环境科学、化学和生物学课程的教案设计。由于几个自由基中间体的产生、复杂的溶剂化效应、不同的产品分布和较低的催化剂周转率，仅使用实验很难研究具有有机生色团的光氧化还原催化循环。尽管在处理电荷转移过程的方法学上取得了进展，但有机生色团的研究主要集中在光电应用上，而光氧化还原循环的机理研究仍然有限。这项工作旨在率先将多相催化中的一个基本原理-萨巴蒂尔原理-应用于光氧化还原系统，并确定控制催化活性和周转次数(或降解阻力)的内在权衡。我们的目标是表征猝灭前激发态生色团和电子给体之间形成的激基络合物，并确定有利于完全猝灭和电荷分离的因素与通过Birch还原降解生色团的对比。为此，我们将采用多种量子化学方法，包括密度泛函理论(DFT)、约束DFT、含时DFT以及基态、激发态和溶剂化体系的能量分解分析。降低降解可能性的因素将与那些提高电子转移到二氧化碳的速率的因素并列在一起，以确定这些性能指标背后的权衡。光氧化还原体系的特性--溶剂、电子供体和生色团性质--有望在活性和降解之间达到理想的平衡。这项计算工作将得到南加州大学合作者的实验瞬变吸收光谱研究的支持。最后，这些设计规则将输入到机器学习方法中，通过在广阔的化学空间中快速搜索具有所需特性的发色团来加速发现。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

项目成果

Modeling and Characterization of Exciplexes in Photoredox CO 2 Reduction: Insights from Quantum Chemistry and Fluorescence Spectroscopy

光氧化还原 CO 2 还原中激基复合物的建模和表征：来自量子化学和荧光光谱的见解

• DOI: 10.1021/acs.jpca.1c10658
• 发表时间: 2022
• 期刊: The Journal of Physical Chemistry A
• 作者: Kron, Kareesa J.;Hunt, Jonathan Ryan;Dawlaty, Jahan M.;Mallikarjun Sharada, Shaama
• 通讯作者: Mallikarjun Sharada, Shaama

Correction to “Modeling and Characterization of Exciplexes in Photoredox CO 2 Reduction: Insights from Quantum Chemistry and Fluorescence Spectroscopy”

修正“光氧化还原 CO 2 还原中激基复合物的建模和表征：来自量子化学和荧光光谱的见解”

• DOI: 10.1021/acs.jpca.3c00590
• 发表时间: 2023
• 期刊: The Journal of Physical Chemistry A
• 作者: Kron, Kareesa J.;Hunt, Jonathan Ryan;Dawlaty, Jahan M.;Mallikarjun Sharada, Shaama
• 通讯作者: Mallikarjun Sharada, Shaama

Organic photoredox catalysts for CO 2 reduction: Driving discovery with genetic algorithms

用于 CO 2 还原的有机光氧化还原催化剂：利用遗传算法推动发现

• DOI: 10.1063/5.0088353
• 发表时间: 2022
• 期刊: The Journal of Chemical Physics
• 作者: Kron, Kareesa J.;Rodriguez-Katakura, Andres;Regu, Pranesh;Reed, Maria N.;Elhessen, Rachelle;Mallikarjun Sharada, Shaama
• 通讯作者: Mallikarjun Sharada, Shaama