Barford William, Gardner John L A, Mannouch Jonathan R
Department of Chemistry, Physical and Theoretical Chemistry Laboratory, University of Oxford, Oxford, OX1 3QZ, UK.
Faraday Discuss. 2019 Dec 16;221(0):281-298. doi: 10.1039/c9fd00054b.
We use the coarse-grained Frenkel-Holstein model to simulate the relaxation, decoherence, and localization of photoexcited states in conformationally disordered π-conjugated polymers. The dynamics are computed via wave-packet propagation using matrix product states and the time evolution block decimation method. The ultrafast (i.e., t < 10 fs) coupling of an exciton to C-C bond vibrations creates an exciton-polaron. The relatively short (ca. 10 monomers) exciton-phonon correlation length causes ultrafast exciton-site decoherence, which is observable on conformationally disordered chains as fluorescence depolarization. Dissipative coupling to the environment (modelled via quantum jumps) causes the localization of quasi-extended exciton states (QEESs) onto local exciton ground states (LEGSs, i.e., chromophores). This is observable as lifetime broadening of the 0-0 transition (and vibronic satellites) of the QEES in two-dimensional electronic coherence spectroscopy. However, as this process is incoherent, neither population increases of the LEGSs nor coherences with LEGSs are observable.
我们使用粗粒化的弗伦克尔 - 霍尔斯坦模型来模拟构象无序的π共轭聚合物中光激发态的弛豫、退相干和局域化。通过使用矩阵乘积态和时间演化块抽取方法的波包传播来计算动力学。激子与C - C键振动的超快（即t < 10 fs）耦合产生了激子 - 极化子。相对较短（约10个单体）的激子 - 声子相关长度导致超快的激子 - 位点退相干，这在构象无序的链上表现为荧光去极化。与环境的耗散耦合（通过量子跳跃建模）导致准扩展激子态（QEESs）局域到局部激子基态（LEGSs，即发色团）上。这在二维电子相干光谱中表现为QEES的0 - 0跃迁（以及振动卫星峰）的寿命展宽。然而，由于这个过程是非相干的，既观察不到LEGSs的布居增加，也观察不到与LEGSs的相干性。
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