CAS: Collaborative Research: Mapping Excited State Trajectories of Multi-metal Centered Complexes by Two-Dimensional Electronic Spectroscopy

在化学学部化学结构、动力学与机制B项目的支持下，西北大学化学系的Lin X. Chen教授和北卡罗莱纳州立大学化学系的Felix N. Castellano教授致力于理解激发态光化学和光物理过程中振动相干性对能量和电子转移反应的影响。该项目旨在获得电子和原子水平上光与物质相互作用的新见解，并利用这些知识通过化学结构调谐和光调制来利用凝聚态、分子光子学和光催化的受控反应性。通过提出的研究获得的知识有可能显著提高我们合理设计用于催化、光电子和能源可持续性的化学材料/设备的能力。拟议的研究让大学研究生参与先进的激光光谱表征，结合最先进的计算化学，并利用先进的化学实验室设施进行分子合成和结构表征，产生多学科的科学专业知识。拟议的研究和教育活动与两所机构的K-12公共宣传活动相结合。该合作团队将利用二维电子光谱（2DES）和宽带瞬态吸收光谱（BBTA）研究三类多发色团合成平台中激发态电子转移的振动相干性影响。三个特定的分子平台是：(1)新一代Pt（II）共面二聚体，具有末端三齿环金属化配体，由单取代吡甲酸酯、羟吡啶、巯基吡啶或二膦桥接，具有金属-金属-配体电荷转移（MMLCT）激发态，其中金属-金属键在光激发后瞬间形成；(2)(1)的铂（II）二聚体，其末端环金属化配体以萘二亚胺（NDI）基电子受体修饰；(3)由Pt（II）单体构建块形成的共面自组装多核聚集体，有或没有电子受体。这些实验系统被设计成在它们的激发态中调谐电子耦合，这要么负责，要么可以与光子激发引起的同相核运动产生的电子和振动相干性相关。在这些设计的分子中，电子和振动相干的检测将使用具有~7飞秒时间分辨率和足够宽的光谱带宽的宽带2DES进行评估。测量的相干性将与光物理过程和光诱导的分子内电子转移化学相关联，使用不断发展的理论来评估电子和/或振动相干性在与光激活相关的这些基本初级过程中的作用。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

With support of the Chemical Structure, Dynamics & Mechanisms B Program of the Chemistry Division, Professor Lin X. Chen of the Department of Chemistry at Northwestern University and Professor Felix N. Castellano of the Department of Chemistry at North Carolina State University seek to understand the effects of vibronic coherence in excited state photochemical and photophysical processes for energy and electron transfer reactions. This project aims to gain new insights into light-matter interactions at the levels of electrons and atoms and use this knowledge to leverage controlled reactivity in condensed phases, molecular photonics, and photocatalysis via both chemical structural tuning and light modulation. The knowledge obtained through the proposed studies has the potential to significantly enhance our ability to rationally design chemical materials/devices for catalysis, optoelectronics, and energy sustainability. The proposed research engages University graduate students in advanced laser spectroscopy for characterization, incorporates state-of-the-art computational chemistry, and utilizes advanced chemistry laboratory facilities for molecular syntheses and structural characterization, engendering multidisciplinary scientific expertise. The proposed research and education activities are integrated with K-12 public outreach events at both institutions. The collaborative team will investigate the effects of vibronic coherence in excited state electron transfer in three classes of multi-chromophore synthetic platforms using two-dimensional electronic spectroscopy (2DES) and broadband transient absorption (BBTA) spectroscopy. The three specific molecular platforms are (1) new generation Pt(II) co-facial dimers featuring terminal tridentate cyclometalating ligands bridged by a single substituted pyrazolate, hydroxypyridine, mercaptopyridine, or diphosphine featuring metal-metal-to-ligand charge transfer (MMLCT) excited states where a metal-metal bond is transiently formed following light excitation; (2) Pt(II) dimers from (1) whose terminal cyclometalating ligands are decorated with naphthalenediimide (NDI)-based electron acceptors; and (3) co-facial self-assembled polynuclear aggregates formed from Pt(II) monomer building blocks with and without electron acceptors. These experimental systems are engineered to tune electronic coupling in their excited states, which are either responsible for or can be correlated to electronic and vibronic coherence originating from in-phase nuclear motions induced by photon excitation. The detection of electronic and vibronic coherences in these designed molecules will be assessed using broadband 2DES featuring ~7 femtosecond time resolution and sufficiently broad spectral bandwidth. The measured coherences will be correlated with photophysical processes and photoinduced intramolecular electron transfer chemistry, rationalized using continuously developing theory to assess the role of electronic and/or vibronic coherence in these fundamental primary processes related to light activation.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.