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中国物理学会期刊

基于量子模型对非富勒烯受体分子内电荷转移的研究

Investigation of intramolecular charge transfer in non-fullerene acceptors based on quantum models

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  • 本文通过紧束缚量子模型研究了非富勒烯受体分子中电荷转移的调控机理,从推拉式电子结构、原子间耦合及电子-晶格相互作用三个方面揭示了影响分子内电荷转移的关键因素。研究发现,增强中间基团的给电子能力或端基的吸电子能力,可通过缩小能级差和增强分子内局域电场的协同效应,显著提升电荷转移量并降低电荷转移态束缚能,从而促进激发态自解离。中间基团原子间跃迁积分(包括杂原子和碳原子)的增大会因轨道局域化或体系刚性化导致电荷转移量出现先减少后趋于平稳的非单调响应;而端基碳原子间跃迁积分增强则能优化给体-受体单元间的相互作用,使电荷转移量单调递增。此外,电子-晶格耦合强度的提升会加剧极化子局域束缚与非辐射能量损失,显著抑制电荷转移。结果表明,高效的非富勒烯分子设计需协同优化推拉式电子结构以最小化电荷转移态束缚能,通过精确调控中间基团的适度离域与端基的强耦合,并辅以分子修饰策略抑制过强的电子-晶格相互作用,从而实现高效的分子内电荷转移与分离。

     

    In this paper, the regulation mechanism of intramolecular charge transfer in non-fullerene acceptors was investigated through a tight-binding quantum model. The key factors influencing intramolecular charge transfer were elucidated from three aspects: push-pull electronic structure, interatomic coupling, and electron-lattice interaction. The study has demonstrated that improving the electron-donating ability of the central group or the electron-withdrawing ability of terminal group can significantly increase the charge transfer amount and reduce the binding energy of the charge transfer state through the synergistic effect of narrowing energy level gaps and strengthening the intramolecular local electric field, thereby facilitating self-dissociation of the excited state. The increase in the interatomic transition integral of the central group (including heteroatoms and carbon atoms) leads to a non-monotonic response of the charge transfer amount, firstly decreasing and then stabilizing. This behavior arises from either orbital localization or system rigidification. However, the increase in the interatomic transition integral of carbon atoms in the terminal group can optimize the interaction between the donor and acceptor units, resulting in monotonically increasing charge transfer amount. In addition, the increase in the electron-lattice coupling strength will intensify polaron localization and non-radiative energy loss, thereby significantly suppressing charge transfer process. The results indicate that the design of high-performance non-fullerene molecules requires coordinated optimization of the push-pull electronic structure to minimize the binding energy of the charge transfer state. By finely tuning the moderate delocalization of central group and the strong coupling of terminal group, along with employing molecular modification strategies to mitigate excessively strong electron-lattice interaction, efficient intramolecular charge transfer and separation can be accomplished.

     

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