Majumder Kanad, Mukherjee Soham, Panjwani Naitik A, Lee Jieun, Bittl Robert, Kim Woojae, Patil Satish, Musser Andrew J
Solid State and Structural Chemistry Unit, Indian Institute of Science, Bangalore 560012, India.
Department of Chemistry and Chemical Biology, Cornell University, Ithaca, New York 14853, United States.
J Am Chem Soc. 2023 Sep 27;145(38):20883-20896. doi: 10.1021/jacs.3c06075. Epub 2023 Sep 13.
Covalent dimers, particularly pentacenes, are the dominant platform for developing a mechanistic understanding of intramolecular singlet fission (iSF). Numerous studies have demonstrated that a photoexcited singlet state in these structures can rapidly and efficiently undergo exciton multiplication to form a correlated pair of triplets within a single molecule, with potential applications from photovoltaics to quantum information science. One of the most significant barriers limiting such dimers is the fast recombination of the triplet pair, which prevents spatial separation and the formation of long-lived triplet states. There is an ever-growing need to develop general synthetic strategies to control the evolution of triplets following iSF and enhance their lifetime. Here, we rationally tune the dihedral angle and interchromophore separation between pairs of pentacenes in a systematic series of bridging units to facilitate triplet separation. Through a combination of transient optical and spin-resonance techniques, we demonstrate that torsion within the linker provides a simple synthetic handle to tune the fine balance between through-bond and through-space interchromophore couplings that steer iSF. We show that the full iSF pathway from femtosecond to microsecond timescales is tuned through the static coupling set by molecular design and structural fluctuations that can be biased through steric control. Our approach highlights a straightforward design principle to generate paramagnetic spin pair states with higher yields.
共价二聚体，尤其是并五苯，是深入理解分子内单重态裂变（iSF）机理的主要平台。大量研究表明，这些结构中的光激发单重态能够快速且高效地发生激子倍增，在单个分子内形成一对相关的三重态，其潜在应用涵盖从光伏到量子信息科学等多个领域。限制此类二聚体应用的最显著障碍之一是三重态对的快速复合，这阻碍了空间分离以及长寿命三重态的形成。因此，开发通用的合成策略来控制iSF后三重态的演化并延长其寿命的需求日益增长。在此，我们通过一系列系统的桥连单元，合理调节并五苯对之间的二面角和发色团间距离，以促进三重态分离。通过瞬态光学和自旋共振技术相结合，我们证明连接体中的扭转提供了一个简单的合成手段，可调节引导iSF的键间和空间发色团间耦合的精细平衡。我们表明，从飞秒到微秒时间尺度的完整iSF路径可通过分子设计设定的静态耦合以及可通过空间控制进行偏向的结构波动来调节。我们的方法突出了一种直接的设计原则，能够以更高产率生成顺磁自旋对态。
