CAREER: Structural and solvent control of nonadiabatic bond formation probed with ultrafast time-resolved spectroscopies

化学系化学结构、动力学和机制（CSDM-A）项目将资助约翰霍普金斯大学的Arthur Bragg教授进行实验研究，研究如何由反应物结构和化学环境控制光驱动的非绝热键形成过程。非绝热过程是能量激发分子的基本弛豫途径，是产生快速高效光化学过程的基础。目标包括提高对能量转换机制的理解，例如光化学和光生物学，以及确定可以控制光驱动化学过程的条件。采用多种最先进的研究方法，为学生研究人员提供高水平的培训机会。这些学生还参与了基于网络摄像头的光谱仪和相关的中学化学课程的开发，使化学，光谱学和仪器设计的基本概念得以探索。通过开发课程单元和培训教育工作者的专业发展讲习班，在JHU教育推广中心（CEO）提供的行政项目协助下，实现教育目标。课程开发的目标是将基本的定量光谱实验整合到课堂项目中，以满足新一代科学标准中概述的新目标。光谱仪和教材将提供给巴尔的摩市学校的教师和学生。本研究的目的是确定与非绝热电环键形成相关的核动力学性质及其整体效能如何受到反应物结构和化学环境的根本影响。这项工作特别侧重于邻芳烃和相关系统的光化学动力学，因为这些系统易于处理，可以进行详细的实验询问。时间分辨吸收光谱和拉曼光谱用于探测几十飞秒时间尺度下的激发态分子动力学，因为这些时间尺度上的键形成和断裂。这些测量和支持性量子化学计算的目标是分子动力学的表征，这些分子动力学发生在激发时电子状态之间的交叉点上，从而产生键形成或其他能量失活途径。这些系统的光诱导动力学也被研究，以探测影响溶液化学过程的溶剂-溶质相互作用。研究结果有望为这些过程的结构和溶剂依赖性提供实验基准，支持从经验和计算两方面预测大分子的弛豫和能量转移途径。

With this CAREER award, the Chemical Structure, Dynamics and Mechanisms (CSDM-A) Program of the Division of Chemistry is funding Professor Arthur Bragg of Johns Hopkins University to conduct experimental investigations on how the course of light-driven nonadiabatic bond formation is controlled by reactant structure and chemical environment. Nonadiabatic processes are fundamental relaxation pathways of energetically excited molecules and give rise to fast and efficient photochemical processes. Aims include improved understanding of energy conversion mechanisms, for example, in photochemistry and photobiology, and determination of conditions under which light-driven chemical processes can be controlled. Multiple state-of-the-art research methods are employed, providing high level training opportunities for student researchers. These students are also involved in development of webcam-based spectrometers and associated secondary-level chemistry curricula, enabling exploration of basic concepts in chemistry, spectroscopy, and instrument design. Educational objectives are met through development of curricular units and professional development workshops for training educators, with administrative program assistance provided by the Center for Educational Outreach (CEO) at JHU. Curriculum development targets integration of basic quantitative spectroscopic experimentation into classroom projects that meet new targets outlined in the Next Generation Science Standards. The spectrometers and curricular materials will be provided to teachers and students in the Baltimore City Schools. The goal of this research is to determine how the nature of nuclear dynamics associated with nonadiabatic electrocyclic bond formation and its overall efficacy are affected fundamentally by reactant structure and chemical environment. The work focuses specifically on the photochemical dynamics of ortho-arenes and related systems, as these are tractable systems for detailed experimental interrogation. Time-resolved absorption and Raman spectroscopies are used to probe dynamics of excited molecules on timescales down to tens of femtoseconds, as these are the timescales on which bonds form and break. These measurements and supportive quantum chemical computations target characterization of molecular dynamics that occur on the approach to and crossing through intersections between electronic states upon excitation, giving rise to bond formation or other energy deactivation pathways. The photoinduced dynamics of these systems is also studied to probe solvent-solute interactions that impact the course of solution-phase chemistry. Findings are expected to provide experimental benchmarks on the structure and solvent dependence of these processes, supporting prediction of relaxation and energy transfer pathways of large molecules both empirically and computationally.