Theoretical Insights into Chemical Functionalization of Carbon Nanotubes: from Chirality Separation to Photoexcited Dynamics

Svetlana V Kilina（北达科他州州立大学法戈分校），Dmitri S Kilin（南达科他州大学）和Andrei Kryjevski（北达科他州州立大学法戈分校）获得了由大分子，超分子和纳米化学（MSN）计划，实验计划办公室共同资助的奖项，以刺激竞争研究（EPSCoR）和化学理论，模型和计算方法（CTMC）计划。该项目是使用计算技术来研究碳纳米管（CNT），这是一种将碳连接在一起的小管。一系列碳-碳键可以围绕管的轴螺旋，并且不同的螺旋速率指示不同类型的CNT。这些管可以用小的有机分子或聚合物的附件（功能化）来装饰，并且可以定制哪些附件和在哪里的选择，以便设计，例如，当外部光照射在CNT上时，什么光出来以及它有多强。追求的另一个目标是使用计算来优化每种类型的CNT的分子装饰，使得化学过程可以用于分离具有不同螺旋速率的CNT的粘性束，这是生产CNT的通常方式。将它们分离是对CNT进行实验的理想选择，因为实验可以提供更多的区分信息。修饰或功能化的CNT的计算使用量子力学和经典力学来解释和预测与实验相关的性质。 这项研究旨在从根本上促进对功能化碳纳米管中太阳能捕获和转化过程的控制，因此与化学相关，通过小的有机表面活性剂和共轭聚合物官能化CNT可以改善其光电和传输性质的化学控制，并且在分离技术中提供用于获得具有类似光电性质的CNT样品的希望。手性本研究的目的是对不同类型的共轭低聚物和聚合物功能化的碳纳米管的形态、电子结构和激发态动力学进行系统的理论研究。使用计算建模，研究人员正在努力了解发生在有机-无机界面的基本物理过程，并管理基于CNT的光电和光伏器件的操作，如激子弛豫和重组，电荷转移，以及从一个吸收的光子（载流子倍增）中产生几个激子。密度泛函理论（DFT）和含时密度泛函理论（TDDFT）被用来计算聚合物-碳纳米管杂化物的精确电子结构和光学响应。此外，量子经典非绝热动力学方法被用来模拟声子介导的动力学，包括在这些系统中的电荷和能量转移。一种新的方法来计算量子效率，由一个光子产生的激子的数量，基于量子场论的多体微扰理论技术的DFT增强被施加到功能化的碳纳米管。各种光谱观测值的计算允许直接比较和验证与超快激光光谱数据（由其他lasboratories）探测功能化碳纳米管的基本电子动力学。同样重要的是，这些计算为实验测量中发生的关键现象提供了明确的解释和预测。

Svetlana V Kilina (North Dakota State University Fargo), Dmitri S Kilin (University of South Dakota) and Andrei Kryjevski (North Dakota State University Fargo) are supported in an award co-funded by the Macromolecular, Supramolecular and Nanochemistry (MSN) Program, the Office of the Experimental Program to Stimulate Competitive Research (EPSCoR) and the Chemical Theory, Models and Computational Methods (CTMC) program. The project is to use computational techniques to investigate carbon nanotubes (CNTs), which are small tubes with carbon connected together. Series of carbon-carbon bonds may spiral around the axis of the tube, and different spiraling rates indicate different types of CNTs. The tubes can be decorated with attachments of small organic molecules or polymers (functionalization), and the choices of which attachments and where can be customized so as to design, for example, what light comes out and how intense it is when an outside light shines on a CNT. Another goal being pursued is to use computations to optimize the molecular decoration for each type of CNT so that chemical processes may be used to separate sticky bundles of CNTs with different rates of spiral, which is the usual way CNTs are produced. Having them separated is ideal for carrying out experiments on CNTs, since experiments can then provide much more discriminating information. The computations for the decorated or functionalized CNTs use both quantum and classical mechanics to interpret and predict properties relevant to experiments. This research aims to facilitate control over the processes of solar energy capture and conversion in functionalized CNTs at the fundamental level, and, thus, will be relevant to chemistry, materials science and engineering.Functionalization of CNTs by small organic surfactants and conjugated polymers can improve chemical control of their optoelectronic and transport properties as well as offer promise in separation techniques for obtaining CNT samples with similar chiralities. The objective of this research is a systematic theoretical investigation of morphology, electronic structure, and excited state dynamics of CNTs functionalized by different types of conjugated oligomers and polymers. Using computational modeling, the investigators are working to understand fundamental physical processes occurring at organic-inorganic interfaces and governing the operation of CNT-based optoelectronic and photovoltaic devices such as exciton relaxation and recombination, charge transfer, and creation of several excitons from one absorbed photon (carrier multiplication). Density functional theory (DFT) and time dependent DFT (TDDFT) are being used for computing accurate electronic structure and optical response of polymer-CNT hybrids. Furthermore, quantum-classical non-adiabatic dynamics methods are being used to model phonon-mediated dynamics including charge and energy transfer in these systems. A novel approach to the calculation of quantum efficiency, the number of excitons generated by a photon, based on DFT augmented by the many body perturbation theory technique of quantum field theory is being applied to functionalized CNTs. Calculations of a variety of spectroscopic observables permit direct comparison and validation with ultrafast laser spectroscopic data (by other lasboratories) probing the fundamental electronic dynamics in functionalized CNTs. Just as importantly, these calculations provide explicit interpretations and predictions of the key phenomena occurring in the experimental measurements.