Hergenhahn Janko, Holmes Jake M, Deng Jie-Ren, Gotfredsen Henrik, Jacobs Robert M J, Kopp Sebastian M, Timmel Christiane R, Anderson Harry L
Centre for Advanced Electron Spin Resonance, Department of Chemistry, University of Oxford, Oxford OX1 3QR, U.K.
Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Oxford OX1 3TA, U.K.
J Am Chem Soc. 2025 Jan 8;147(1):978-987. doi: 10.1021/jacs.4c14161. Epub 2024 Dec 30.
The delocalization length of charge carriers in organic semiconductors influences their mobility and is an important factor in the design of functional materials. Here, we have studied the radical anions of a series of linear and cyclic butadiyne-linked porphyrin oligomers using CW-EPR, H Mims ENDOR and NIR/MIR spectroelectrochemistry together with DFT calculations and multiscale molecular modeling. Low-temperature hyperfine EPR spectroscopy and optical data show that polarons are delocalized nonuniformly over about four porphyrins with most of the spin density on just two units even in the cyclic structures, in which all porphyrin sites are identical. Room temperature CW-EPR spectra indicate a larger spatial distribution of spin density on the EPR time scale. We introduce a combined molecular dynamics simulations and DFT approach to demonstrate that dynamic migration of delocalized polarons can occur in porphyrin oligomers and that this fully accounts for the apparent spin density distribution at room temperature. This method is a powerful tool in both the study and development of molecular wires and molecular electronics.
有机半导体中电荷载流子的离域长度会影响其迁移率，并且是功能材料设计中的一个重要因素。在此，我们使用连续波电子顺磁共振（CW-EPR）、H Mims电子核双共振（ENDOR）和近红外/中红外光谱电化学，结合密度泛函理论（DFT）计算和多尺度分子建模，研究了一系列线性和环状丁二炔连接的卟啉低聚物的自由基阴离子。低温超精细EPR光谱和光学数据表明，极化子在大约四个卟啉上非均匀离域，即使在环状结构中所有卟啉位点都相同的情况下，大部分自旋密度也仅在两个单元上。室温CW-EPR光谱表明在EPR时间尺度上自旋密度有更大的空间分布。我们引入了一种结合分子动力学模拟和DFT的方法，以证明离域极化子的动态迁移可以在卟啉低聚物中发生，并且这完全解释了室温下的表观自旋密度分布。该方法是分子导线和分子电子学研究与开发中的有力工具。
