Probing excitation delocalization in supramolecular chiral stacks by means of circularly polarized light: Experiment and modeling
Probing excitation delocalization in supramolecular chiral stacks by means of circularly polarized light: Experiment and modeling
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DOI：
10.1021/ja067321g
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发表时间：
2007-06-06
影响因子：
15
通讯作者：
Beljonne, David
中科院分区：
文献类型：
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作者：
Spano, Frank C.;Meskers, Stefan C. J.;Beljonne, David
功能化、手性低聚亚苯基乙烯撑 (MOPV) 的螺旋聚集体中的光激发以修饰（极化）弗伦克尔激子的形式超越了玻恩-奥本海默近似。这样可以对实验观察到的荧光圆偏振的波长依赖性进行精确建模，从而直接探测该系统中电子振动 (EV) 耦合的非绝热性质。荧光光子从核几何结构中发射，其中一个 MOPV 及其两个最近的邻居具有由于激发态的存在而与基态明显不同的核平衡。吸收和发射带形状以及圆二色性与大约两个相邻分子的发射激发的相干范围一致。 MOPV 的零级激发态能量（无序）的随机波动限制了激子离域，并且可以通过宽度 sigma = 0.12 eV 和空间相关长度 l(0) 近似于 5 个分子的能量高斯分布来描述。我们发现无序和 EV 耦合在将发射激子集中到单个 MOPV 上的概率为 95% 时协同作用。
Photoexcitations in helical aggregates of a functionalized, chiral oligophenylenevinylene (MOPV) are described going beyond the Born-Oppenheimer approximation, in the form of dressed (polaronic) Frenkel excitons. This allows for accurate modeling of the experimentally observed wavelength dependence of the circular polarization in fluorescence, which directly probes the non-adiabatic nature of the electron-vibration (EV) coupling in this system. The fluorescence photon is emitted from a nuclear geometry in which one MOPV and its two nearest neighbors have a nuclear equilibrium that differs appreciably from the ground state due to the presence of the excited state. The absorption and emission band shape and the circular dichroism are consistent with a coherence range of the emitting excitation of approximately two neighboring molecules. Random fluctuations in the zero-order excited-state energy of the MOPVs (disorder) limit the exciton delocalization and can be described by a Gaussian distribution of energies with a width sigma = 0.12 eV and a spatial correlation length l(0) approximate to 5 molecules. We find that disorder and EV coupling act synergistically in localizing the emitting exciton to a single MOPV in the aggregate with 95% probability.