Essential States Model for Merocyanine Dye Stacks: Bridging Electronic and Optical Absorption Properties
Essential States Model for Merocyanine Dye Stacks: Bridging Electronic and Optical Absorption Properties
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DOI：
10.1021/acs.jpcc.9b04430
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发表时间：
2019-08-01
影响因子：
3.7
通讯作者：
Spano, Frank C.
中科院分区：
文献类型：
--
作者：
Bialas, David;Zhong, Chuwei;Spano, Frank C.
发展了一个扩展的基本态模型，用于研究高偶极花菁染料和由适当间隔链系留双(花菁)染料的折叠和自组装形成的双和四pi堆栈的吸收和电子性质。我们的分析表明，简单的两态模型不足以充分描述单个发色团的吸收特征。然而，通过引入额外的桥态，吸收特性得到了很好的描述，并且得到了永久偶极矩和跃迁偶极矩的合理值。结果表明，折叠双堆栈的低能吸收带是由振动耦合引起的，而自组装四重堆栈的光谱中观察到的额外吸收肩是由于跃迁到较低激发态。此外，相对于由极化效应引起的单个生色团，两个pi堆栈中的发色团在基态时的电荷转移特性有所增加，这在传统的Frenkel激子理论中是不能解释的。这些见解对于基于花菁和偶极生色团的功能材料的正确设计具有重要意义。
An extension of the essential states model is developed to investigate the absorption and electronic properties of a highly dipolar merocyanine dye and double and quadruple pi-stacks formed upon the folding and self-assembly of appropriate spacer-tethered bis(merocyanine) dyes. Our analysis reveals that a simple two-state model is not sufficient to adequately describe the absorption features of a single chromophore. However, by including an additional bridge state, the absorption features are well described and reasonable values for the permanent and transition dipole moments are obtained. We show that the low-energy absorption band of the folded double stack results from vibronic coupling, whereas the additional absorption shoulder observed in the spectrum of the self-assembled quadruple stack is due to a transition to a lower excited state. Furthermore, the chromophores within both pi-stacks exhibit an increase in the charge-transfer character in the ground state with respect to the single chromophore arising from polarizability effects, which are not accounted for in the conventional Frenkel exciton theory. These insights are of significant importance for the proper design of functional materials based on merocyanines and dipolar chromophores in general.