Bridging the gap between H- and J-aggregates: Classification and supramolecular tunability for excitonic band structures in two-dimensional molecular aggregates
Bridging the gap between H- and J-aggregates: Classification and supramolecular tunability for excitonic band structures in two-dimensional molecular aggregates
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DOI：
10.1063/5.0094451
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发表时间：
2022-06-01
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影响因子：
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通讯作者：
Caram, Justin R.
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文献类型：
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作者：
Deshmukh, Arundhati P.;Geue, Niklas;Caram, Justin R.
具有远程激子偶联的分子聚集体与它们的单体对应物相比具有截然不同的光物理性质。从Kasha的一维系统模型来看，正或负激子耦合导致单体的光谱蓝移或红移，分别标记为h和j聚集体。高维系统中的整体激子耦合要复杂得多，不能仅仅从它们的谱移来简单地分类。在这里，我们使用温度相关的峰移，热展宽和量子产率为扩展的2D聚集体提供了统一的分类。我们讨论了六个二维聚集体的例子，它们具有类j吸收光谱，但量子产率和超辐度发生了很大的变化。我们发现差异的根源实际上是不同的激子能带结构，其中亮态的能量低于单体，但仍然远离能带边缘。我们称之为“I-aggregate”。我们的结果提供了一个复杂的激子行为的描述，不能解释仅仅在卡莎的模型。此外，这些特性可以通过聚集体内部的填充几何形状来调节，为控制它们提供了超分子途径。这将允许在光电子、光子学、激子能量转移和短波红外技术领域的应用中精确优化聚集体特性。由AIP出版社独家授权出版。
Molecular aggregates with long-range excitonic couplings have drastically different photophysical properties compared to their monomer counterparts. From Kasha's model for one-dimensional systems, positive or negative excitonic couplings lead to blue or red-shifted optical spectra with respect to the monomers, labeled H-and J-aggregates, respectively. The overall excitonic couplings in higher dimensional systems are much more complicated and cannot be simply classified from their spectral shifts alone. Here, we provide a unified classification for extended 2D aggregates using temperature dependent peak shifts, thermal broadening, and quantum yields. We discuss the examples of six 2D aggregates with J-like absorption spectra but quite drastic changes in quantum yields and superradiance. We find the origin of the differences is, in fact, a different excitonic band structure where the bright state is lower energy than the monomer but still away from the band edge. We call this an "I-aggregate." Our results provide a description of the complex excitonic behaviors that cannot be explained solely on Kasha's model. Furthermore, such properties can be tuned with the packing geometries within the aggregates providing supramolecular pathways for controlling them. This will allow for precise optimizations of aggregate properties in their applications across the areas of optoelectronics, photonics, excitonic energy transfer, and shortwave infrared technologies. Published under an exclusive license by AIP Publishing.