Micron School of Materials Science & Engineering, Boise State University, Boise, ID 83725, USA.
Department of Chemistry & Biochemistry, Boise State University, Boise, ID 83725, USA.
Molecules. 2022 Oct 5;27(19):6612. doi: 10.3390/molecules27196612.
Molecular aggregates are of interest to a broad range of fields including light harvesting, organic optoelectronics, and nanoscale computing. In molecular aggregates, nonradiative decay pathways may emerge that were not present in the constituent molecules. Such nonradiative decay pathways may include singlet fission, excimer relaxation, and symmetry-breaking charge transfer. Singlet fission, sometimes referred to as excitation multiplication, is of great interest to the fields of energy conversion and quantum information. For example, endothermic singlet fission, which avoids energy loss, has been observed in covalently bound, linear perylene trimers and tetramers. In this work, the electronic structure and excited-state dynamics of dimers of a perylene derivative templated using DNA were investigated. Specifically, DNA Holliday junctions were used to template the aggregation of two perylene molecules covalently linked to a modified uracil nucleobase through an ethynyl group. The perylenes were templated in the form of monomer, transverse dimer, and adjacent dimer configurations. The electronic structure of the perylene monomers and dimers were characterized via steady-state absorption and fluorescence spectroscopy. Initial insights into their excited-state dynamics were gleaned from relative fluorescence intensity measurements, which indicated that a new nonradiative decay pathway emerges in the dimers. Femtosecond visible transient absorption spectroscopy was subsequently used to elucidate the excited-state dynamics. A new excited-state absorption feature grows in on the tens of picosecond timescale in the dimers, which is attributed to the formation of perylene anions and cations resulting from symmetry-breaking charge transfer. Given the close proximity required for symmetry-breaking charge transfer, the results shed promising light on the prospect of singlet fission in DNA-templated molecular aggregates.
分子聚集体引起了广泛领域的兴趣，包括光捕获、有机光电和纳米级计算。在分子聚集体中，可能会出现组成分子中不存在的非辐射衰减途径。这些非辐射衰减途径可能包括单重态裂变、激基复合物松弛和对称性破缺的电荷转移。单重态裂变，有时也称为激发倍增，在能量转换和量子信息领域引起了极大的关注。例如，在共价键合的线性苝三聚物和四聚物中观察到了避免能量损失的吸热单重态裂变。在这项工作中，使用 DNA 模板化的苝衍生物二聚体的电子结构和激发态动力学进行了研究。具体来说，DNA 霍利迪结被用来模板化两个通过乙炔基共价连接到修饰尿嘧啶碱基上的苝分子的聚集。苝被模板化成单体、横向二聚体和相邻二聚体构型。苝单体和二聚体的电子结构通过稳态吸收和荧光光谱进行了表征。通过相对荧光强度测量初步了解了它们的激发态动力学，这表明在二聚体中出现了新的非辐射衰减途径。随后使用飞秒可见瞬态吸收光谱来阐明激发态动力学。在二聚体中，一个新的激发态吸收特征在数十皮秒的时间尺度上增长，这归因于对称性破缺的电荷转移导致苝阴离子和阳离子的形成。鉴于对称性破缺的电荷转移所需的接近程度，这些结果为 DNA 模板化分子聚集体中单重态裂变的前景提供了有希望的线索。
