Photoexcitation Mechanisms and Transport Properties of Polarons and Solitons in Conjugated Polymers

本文主要研究共轭聚合物中载流子的光产生机理和载流子动力学。这些将通过两个实验来研究：1。亚皮秒时间内快速瞬态载流子密度测量，利用6-10 ？M光谱区，它跨越了聚合物主链上载流子产生的红外主动振动模式；2. 瞬态光电导率测量。前者测量将确定载流子量子效率对光子能量和链间耦合强度的依赖关系，以及载流子重组动力学，后者测量将探测载流子动力学。本研究的目的是探讨共轭聚合物领域的一些最基本的问题：孤子是主要激励吗？孤子-孤子相互作用的本质是什么？能否在高孤子激发密度下跨越绝缘体-金属跃迁？在严格的一维系统中载流子生成是否可能（例如在单个聚合物链上）？这项研究涉及到最先进的实验技术，因此将为参与该项目的学生和博士后提供显著的教育效益。本研究主要通过瞬态载流子密度和瞬态光电导率的测量来研究各种共轭聚合物中的载流子光产生机制和载流子动力学。本研究的目的是探讨共轭聚合物领域的一些最基本的问题：孤子是主要激励吗？孤子-孤子相互作用的本质是什么？能否在高孤子激发密度下跨越绝缘体-金属跃迁？在严格的一维系统中载流子生成是否可能（例如在单个聚合物链上）？或者更确切地说，是否需要链间耦合来避免载体的重新组合？改变链间耦合对载流子量子效率、载流子重组动力学和载流子输运有何影响？中性激子在载流子光激发过程中的作用是什么？拟议的研究将提供一种数据，应该结束这些核心问题。此外，拟议的研究涉及最先进的实验技术，因此将为加州大学圣巴巴拉分校聚合物和有机固体研究所的学生和博士后提供显著的教育效益。

The proposed research is focused on the carrier photogeneration mechanism as well as the carrier dynamics in conjugated polymers. These will be investigated by means of two experiments: 1. Fast transient carrier density measurements in the sub-picosecond time regime, using transient photoinduced absorption probed in the 6-10 ?m spectral region, which spans the infrared active vibrational modes that arise from carriers on the polymer backbone; 2. transient photoconductivity measurements. The former measurement will determine the dependence of the carrier quantum efficiency on photon energy and interchain coupling strength, as well as carrier recombination dynamics, while the latter one will probe the carrier dynamics. The goal of this research is to investigate some of the most fundamental questions in the field of conjugated polymers: Are solitons primary excitations? What is the nature of soliton-soliton interaction? Can one cross the insulator-metal transition at high soliton excitation densities? Is carrier generation possible in strictly one-dimensional systems (e.g. on a single polymer chain)? The proposed research involves state-of-the-art experimental techniques, and thus will provide significant educational benefit to the students and post-doctoral fellows involved in the project. %%%This research is focused on the carrier photogeneration mechanism and carrier dynamics in various conjugated polymers by means of transient carrier density as well as transient photoconductivity measurements. The goal of this research is to investigate some of the most fundamental questions in the field of conjugated polymers: Are solitons primary excitations? What is the nature of soliton-soliton interaction? Can one cross the insulator-metal transition at high soliton excitation densities? Is carrier generation possible in strictly one-dimensional systems (e.g. on a single polymer chain)? Or rather, is interchain coupling inherently required for carriers to escape geminate recombination? How are the carrier quantum efficiency, carrier recombination dynamics, and carrier transport affected by modifying the inter-chain coupling? What is the role of neutral excitons in the carrier photoexcitation process? The proposed research will provide the kind of data that should bring a closure to these core questions. Additionally, the proposed research involves state-of-the-art experimental techniques, and thus will provide significant educational benefit to the students and post-doctoral fellows in the Institute for Polymers and Organic Solids at UC Santa Barbara.