A solvent–solute cooperative mechanism for symmetry-breaking charge transfer†,Physical Chemistry Chemical Physics

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A solvent–solute cooperative mechanism for symmetry-breaking charge transfer†
Physical Chemistry Chemical Physics ( IF 2.9 ) Pub Date : 2019-12-12 , DOI: 10.1039/c9cp05090f
Changmin Lee _{1,

2,

3,

4} , Cheol Ho Choi _{1,

4,

5,

6} , Taiha Joo _{1,

2,

3,

4}

Affiliation

Symmetry-breaking charge transfer (SBCT) is an important process at the early stages of the photoinduced processes in multichromophore systems such as the photosynthetic apparatus. We investigated the photoinduced SBCT dynamics of 9,9′-bianthracene (BA), a representative molecule showing SBCT, by time-resolved fluorescence (TF) with the highest time-resolution and excited-state quantum mechanics/effective fragment potential molecular dynamics (MD) simulation. TF experiments show that the SBCT kinetics matches quantitatively with the solvation function excluding the initial ultrafast component that is assigned to the inertial motion of the solvent. Therefore, it is established that the SBCT of BA is coupled solely with the rotational diffusion of solvent molecules excluding the inertial motion of solvents. MD simulations show that random rotational fluctuation of solvents mostly in the first solvation shell generates a transient electric field as high as 1.0 × 10⁹ V m⁻¹, which provides an asymmetric environment required for the generation of a CT state in this symmetric dimer. Once the CT state is formed, the dipole moment in the solute causes further rotation of solvent molecules leading to an augmented electric field, which in turn further stabilizes the CT state prohibiting the reverse reaction.

中文翻译：

打破对称电荷转移的溶剂-溶质协同机制†

打破对称电荷转移（SBCT）是多发色团系统（例如光合装置）中光诱导过程早期的重要过程。我们通过具有最高时间分辨率和激发态量子力学/有效片段势分子动力学的时间分辨荧光（TF）研究了9,9'-联蒽（BA）（显示SBCT的代表性分子）的光诱导SBCT动力学（ MD）模拟。TF实验表明，SBCT动力学与溶剂化功能定量匹配，但不包括分配给溶剂惯性运动的初始超快组分。因此，可以确定BA的SBCT仅与溶剂分子的旋转扩散（不包括溶剂的惯性运动）耦合。⁹ V m^-1，提供了在该对称二聚体中产生CT状态所需的非对称环境。一旦形成CT状态，溶质中的偶极矩会使溶剂分子进一步旋转，从而导致电场增强，进而使CT状态更稳定，从而阻止逆反应。

更新日期：2020-01-08

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