First-Principles Calculation of the Optical Properties of an Amphiphilic Cyanine Dye Aggregate
First-Principles Calculation of the Optical Properties of an Amphiphilic Cyanine Dye Aggregate
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DOI：
10.1021/jp4112487
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发表时间：
2014-02-13
影响因子：
2.9
通讯作者：
Knoester, Jasper
中科院分区：
文献类型：
--
作者：
Haverkort, Frank;Stradomska, Anna;Knoester, Jasper
使用第一性原理方法，我们计算的电子和光学性质的分子聚集体的染料两亲-pseudoisocyanine，其结构，我们从分子动力学（MD）模拟的自聚集过程。使用量子化学方法，我们翻译成一个有效的含时的Frenkel激子哈密顿量的结构信息的主要光学跃迁的聚合物。该哈密顿量用于计算吸收光谱。详细分析的动态波动的分子跃迁能量和分子间的激发转移相互作用，在这个哈密顿量使我们能够阐明相关的时间尺度的起源;短的时间尺度，在高达几百飞秒的顺序，导致内部运动的染料分子，而较长的时间尺度（几皮秒），我们归因于环境运动。从MD获得的聚集体结构的吸收光谱特征蓝移峰相比，单体，因此，我们的聚集体可以被归类为H-聚集体，虽然相当大的振子强度进行状态沿着整个激子带。与实验结果的比较表明，模拟的吸收光谱线的形状太宽，指向太多的模拟聚集体的内部结构的混乱。
Using a first-principles approach, we calculate electronic and optical properties of molecular aggregates of the dye amphi-pseudoisocyanine, whose structures we obtained from molecular dynamics (MD) simulations of the self-aggregation process. Using quantum chemistry methods, we translate the structural information into an effective time-dependent Frenkel exciton Hamiltonian for the dominant optical transitions in the aggregate. This Hamiltonian is used to calculate the absorption spectrum. Detailed analysis of the dynamic fluctuations in the molecular transition energies and intermolecular excitation transfer interactions in this Hamiltonian allows us to elucidate the origin of the relevant time scales; short time scales, on the order of up to a few hundreds of femtoseconds, result from internal motions of the dye molecules, while the longer (a few picosecond) time scales we ascribe to environmental motions. The absorption spectra of the aggregate structures obtained from MD feature a blue-shifted peak compared to that of the monomer; thus, our aggregates can be classified as H-aggregates, although considerable oscillator strength is carried by states along the entire exciton band. Comparison to the experimental absorption spectrum of amphi-PIC aggregates shows that the simulated line shape is too wide, pointing to too much disorder in the internal structure of the simulated aggregates.