Ballistic Energy\nTransport via Long Alkyl Chains:\nA New Initiation Mechanism

In an effort to increase the speed and efficiency of\nballistic\nenergy transport via oligomeric chains, we performed measurements\nof the transport in compounds featuring long alkyl chains of up to\n37 methylene units. Compounds of the N<sub>3</sub>-(CH<sub>2</sub>)<sub><i>n</i></sub>-COOMe type (denoted as az<i>n</i>ME) were synthesized with <i>n</i> = 5, 10, 15, 19, 28,\n37 and studied using relaxation-assisted two-dimensional infrared\nspectroscopy. The speed of the ballistic transport, initiated by the\nN<sub>3</sub> tag excitation, increased ca. 3-fold for the longer\nchains (<i>n</i> = 19–37) compared to the shorter\nchains, from 14.7 to 48 Å/ps, in line with an earlier prediction\n(Nawagamuwage et al. 2021, <i>J. Phys. Chem. B</i>, <b>125</b>, 7546). Modeling, based on solving numerically the Liouville\nequation, was capable of reproducing the experimental data only if\nthree wavepackets are included, involving CH<sub>2</sub> twisting\n(Tw), wagging (W), and rocking (Ro) chain bands. The approaches for\ndesigning molecular systems featuring a higher speed and efficiency\nof energy transport are discussed.