Hassani Majid, Shaon Pathick Halder, Mallon Christopher J, Shi Tianjiao, Monzy Judith N, Fenlon Edward E, Leitner David M, Tucker Matthew J
Department of Chemistry, University of Nevada, Reno, Reno, Nevada 89557, USA.
Department of Chemistry, Franklin & Marshall College, Lancaster, Pennsylvania 17604-3003, USA.
J Chem Phys. 2025 Apr 21;162(15). doi: 10.1063/5.0263013.
Elucidating the nature of intramolecular vibrational energy redistribution (IVR) can guide the design of molecular wires. The ability to steer these processes through a mechanistic understanding of IVR is assessed by utilizing two-dimensional infrared (2D IR) spectroscopy. 2D IR spectroscopy allows for the direct investigation of timescales of energy transfer within three aromatic molecular scaffolds: 4'-azido-[1,1'-biphenyl]-4-carbonitrile (PAB), 2'-azido-[1,1'-biphenyl]-4-carbonitrile (OAB), and 4'-(azidomethyl)-[1,1'-biphenyl]-4-carbonitrile (PAMB). Energy transfer pathways between azido (N3)- and cyano (CN)-vibrational reporters uncover the importance of Fermi resonances, anharmonic coupling, and specific structural components in directing energy flow. Among these systems, PAB exhibits the fastest energy transfer (22 ps), facilitated by its co-planar biphenyl structure, enabling strong π-π stacking interactions to optimize vibrational coupling. In contrast, OAB demonstrates a moderate IVR timescale (38 ps) due to an orthogonal molecular plane and steric hindrance, which disrupts coupling pathways. PAMB, with a para-methylene group, introduces a structural bottleneck that significantly impedes energy flow, slowing down the energy transfer to 84 ps. The observed IVR rates align with computational predictions, highlighting intermediate ring modes in PAB as efficient energy transfer bridges, a mechanism that is less pronounced in OAB and PAMB. This study demonstrates that IVR is dictated not only by anharmonic coupling strengths but also by the extended alignment of vibrational modes across molecular planes and their delocalization within aromatic scaffolds. By modulating structural features, such as steric constraints and π-π interactions, we provide a framework for tailoring energy flow in conjugated molecular systems. These findings offer new insights into IVR dynamics for applications in molecular electronics.
阐明分子内振动能量再分配（IVR）的本质可以指导分子导线的设计。通过利用二维红外（2D IR）光谱来评估通过对IVR的机理理解来操控这些过程的能力。二维红外光谱允许直接研究三种芳香族分子支架内的能量转移时间尺度：4'-叠氮基-[1,1'-联苯]-4-腈（PAB）、2'-叠氮基-[1,1'-联苯]-4-腈（OAB）和4'-(叠氮甲基)-[1,1'-联苯]-4-腈（PAMB）。叠氮基（N3）和氰基（CN）振动报告基团之间的能量转移途径揭示了费米共振、非谐耦合和特定结构成分在引导能量流动中的重要性。在这些体系中，PAB表现出最快的能量转移（22皮秒），这得益于其共平面的联苯结构，能够实现强烈的π-π堆积相互作用以优化振动耦合。相比之下，由于分子平面正交和空间位阻，OAB表现出中等的IVR时间尺度（38皮秒），这会破坏耦合途径。带有对亚甲基的PAMB引入了一个结构瓶颈，显著阻碍了能量流动，使能量转移减慢至84皮秒。观察到的IVR速率与计算预测结果一致，并突出了PAB中的中间环模式作为有效的能量转移桥梁，而在OAB和PAMB中这种机制不太明显。这项研究表明，IVR不仅由非谐耦合强度决定，还由振动模式在分子平面上的扩展排列及其在芳香族支架内的离域化决定。通过调节结构特征，如空间位阻和π-π相互作用，我们提供了一个在共轭分子体系中定制能量流动的框架。这些发现为分子电子学应用中的IVR动力学提供了新的见解。
