Vibronic exciton model for low bandgap donor-acceptor polymers.
Vibronic exciton model for low bandgap donor-acceptor polymers.
复制标题
低带隙供体-受体聚合物的振动激子模型。
作者：
Mohammad Balooch Qarai;Xin Chang;F. Spano
引入了一个振动激子模型来描述低带隙给受体共轭聚合物的激发态能带结构和相关吸收光谱。哈密顿量用非绝热基表示，由类似frenkel的供体和受体片段激发以及相邻片段之间的电荷转移（CT）激发组成。态通过电子和空穴转移以及通过相互作用的碎片跃迁偶极矩以库伦方式相互耦合。还包括局部振动耦合，涉及突出的芳香-quinoidal振动模式，这是大多数共轭低聚物和聚合物中明显的振动进展的原因。DAD重复单元表现为j聚集三聚体，由供体和受体片段之间相当大的同相电子和空穴转移积分以及供体和受体片段激发之间的负库仑耦合驱动。在聚合物极限下，通过重复单元间耦合增强了j -聚集体的行为，在最低能量的近红外波段显著增强了0-0振动峰。此外，辐射速率通过相干连接重复单元的数量而增强。近红外波段显示出CT和Frenkel-like激发大致相等的外合。对聚合物PffBT4T-2DT进行了应用，模拟的吸收光谱定量地捕捉了测量光谱的显著特征。
A vibronic exciton model is introduced to describe the excited state band structure and associated absorption spectra of low bandgap donor-acceptor conjugated polymers. The Hamiltonian is represented in a diabatic basis consisting of Frenkel-like donor and acceptor fragment excitations as well as charge-transfer (CT) excitations between neighboring fragments. States are coupled to each other through electron and hole transfer as well as Coulombically, through interacting fragment transition dipole moments. Local vibronic coupling involving the prominent aromatic-quinoidal vibrational mode, which is responsible for pronounced vibronic progressions in most conjugated oligomers and polymers, is also included. The DAD repeat unit is shown to behave like a J-aggregate trimer, driven by both the sizable in-phase electron and hole transfer integrals between donor and acceptor fragments as well as negative Coulomb coupling between donor and acceptor fragment excitations. The J-aggregate behavior is enhanced in the polymer limit through inter-repeat unit coupling, with the 0-0 vibronic peak significantly enhanced in the lowest-energy near-IR band. In addition, the radiative rate is enhanced by the number of coherently connected repeat units. The near-IR band is shown to possess roughly equal admixtures of CT and Frenkel-like excitations. Applications are made to the polymer PffBT4T-2DT, with the simulated absorption spectrum quantitatively capturing the salient features of the measured spectrum.