Yue Yuankai, Qasim Layla N, Kurnosov Arkady A, Rubtsova Natalia I, Mackin Robert T, Zhang Hong, Zhang Boyu, Zhou Xiao, Jayawickramarajah Janarthanan, Burin Alexander L, Rubtsov Igor V
Department of Chemistry, Tulane University, New Orleans, Louisiana 70118, United States.
J Phys Chem B. 2015 May 28;119(21):6448-56. doi: 10.1021/acs.jpcb.5b03658. Epub 2015 May 14.
Intramolecular transport of vibrational energy in two series of oligomers featuring alkane chains of various length was studied by relaxation-assisted two-dimensional infrared spectroscopy. The transport was initiated by exciting various end-group modes (tags) such as different modes of the azido (ν(N≡N) and ν(N═N)), carboxylic acid (ν(C═O)), and succinimide ester (νas(C═O)) with short mid-IR laser pulses. It is shown that the transport via alkane chains is ballistic and the transport speed is dependent on the type of the tag mode that initiates the transport. The transport speed of 8.0 Å/ps was observed when initiated by either ν(C═O) or νas(C═O). When initiated by ν(N≡N) and ν(N═N), the transport speed of 14.4 ± 2 and 11 ± 4 Å/ps was observed. Analysis of the vibrational relaxation channels of different tags, combined with the results for the group velocity evaluation, permits identification of the chain bands predominantly contributing to the transport for different cases of the transport initiation. For the transport initiated by ν(N≡N) the CH2 twisting and wagging chain bands were identified as the major energy transport channels. For the transport initiated by ν(C═O), the C-C stretching and CH2 rocking chain bands served as major energy transporters. The transport initiated by ν(N═N) results in direct formation of the wave packet within the CH2 twisting and wagging chain bands. These developments can aid in designing molecular systems featuring faster and more controllable energy transport in molecules.
通过弛豫辅助二维红外光谱研究了具有不同长度烷烃链的两个系列低聚物中振动能量的分子内传输。传输通过用短中红外激光脉冲激发各种端基模式（标记）来启动，例如叠氮基的不同模式（ν(N≡N)和ν(N═N)）、羧酸（ν(C═O)）和琥珀酰亚胺酯（νas(C═O)）。结果表明，通过烷烃链的传输是弹道式的，传输速度取决于启动传输的标记模式类型。当由ν(C═O)或νas(C═O)启动时，观察到的传输速度为8.0 Å/ps。当由ν(N≡N)和ν(N═N)启动时，观察到的传输速度分别为14.4 ± 2 Å/ps和11 ± 4 Å/ps。对不同标记的振动弛豫通道进行分析，并结合群速度评估结果，可以确定在不同传输启动情况下对传输起主要作用的链带。对于由ν(N≡N)启动的传输，CH2扭转和摆动链带被确定为主要的能量传输通道。对于由ν(C═O)启动的传输，C-C伸缩和CH2摇摆链带是主要的能量传输通道。由ν(N═N)启动的传输导致在CH2扭转和摆动链带内直接形成波包。这些进展有助于设计在分子中具有更快、更可控能量传输特性的分子系统。
