Perylene Diimide-Based Hj- and hJ-Aggregates: The Prospect of Exciton Band Shape Engineering in Organic Materials
Perylene Diimide-Based Hj- and hJ-Aggregates: The Prospect of Exciton Band Shape Engineering in Organic Materials
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DOI：
10.1021/acs.jpcc.9b04429
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发表时间：
2019-08-22
影响因子：
3.7
通讯作者：
Spano, Frank C.
中科院分区：
文献类型：
--
作者：
Oleson, April;Zhu, Tong;Spano, Frank C.
共轭有机发色团π叠层中的激子带色散是决定光物理响应和输运性质的关键因素。在这样的堆叠中，激子带宽，特别是在带中心的曲率，是由由于波函数重叠和长程库仑耦合过渡偶极-偶极相互作用所产生的短程耦合之间的干扰确定。干涉可以是完全破坏性的，产生无色散的“平”带，导致聚集体显示单体样性质的不寻常情况，尽管具有紧密间隔的发色团。诸如此类的偶联发色团被称为“空聚集体”，并且导致它们的相互作用的完美平衡被称为“空点”。在这里，我们研究了两个二萘嵌苯二酰亚胺（PDI）的衍生物，其中正长程耦合诱导H-聚集体行为，而抵消短程耦合诱导J-聚集体行为。因此，这两种衍生物都显示出所谓的HJ-聚合物特性，但在这里显示为跨越零点。在N-苯基PDI π-堆叠中，较强的库仑耦合使尺度倾斜，有利于整体H-样行为，从而产生Hj-聚集体，其特征在于弱的0-0振动光致发光（PL）峰，其随温度增加。相比之下，在四苯基PDI π堆叠中，短程耦合占主导地位，导致hJ聚集体，其特征在于占主导地位的0-0发射。此外，在四苯基PDI中，0-0/0-1 PL比率保持约为单体值的两倍，与温度无关，表明强烈的Peierls样二聚化。识别PDI衍生物中的零点为通过例如化学诱导或压力诱导的分子堆积变化的带形工程提供参考几何形状。
The exciton band dispersion in pi-stacks of conjugated organic chromophores is a critical factor in determining the photophysical response and transport properties. In such stacks, the exciton band width and, in particular, the curvature at the band center, is determined by an interference between short-range coupling due to wave function overlap and long-range Coulomb coupling arising from transition dipole-dipole interactions. The interference can be completely destructive, yielding a dispersionless "flat" band resulting in an unusual situation where the aggregate displays monomer-like properties, despite having closely spaced chromophores. Coupled chromophores such as these are called "null aggregates" and the perfect balance of interactions that leads to them are referred to as "null points". Here, we study two perylene diimide (PDI) derivatives where positive long-range coupling induces H-aggregate behavior, whereas counteracting short-range coupling induces J-aggregate behavior. As such, both derivatives display so-called HJ-aggregate properties but are shown here to straddle a null point. In N-phenyl PDI pi-stacks, the stronger Coulomb coupling tilts the scales in favor of overall H-like behavior resulting in Hj-aggregates, characterized by a weak 0-0 vibronic photoluminescence (PL) peak, which increases with temperature. By contrast, in tetraphenyl PDI pi-stacks, the short-range coupling dominates, resulting in hJ-aggregates, as characterized by dominant 0-0 emission. Furthermore, in tetraphenyl PDI, the 0-0/0-1 PL ratio remains approximately twice the monomer value, independent of temperature, indicating strong Peierls-like dimerization. Identifying the null points in PDI derivatives provides reference geometries for band shape engineering through, for example, chemically induced or pressure induced changes in molecular packing.