Ballistic Energy Transport via Long Alkyl Chains: A New Initiation Mechanism

In an effort to increase the speed and efficiency of ballistic energy transport via oligomeric chains, we performed measurements of the transport in compounds featuring long alkyl chains of up to 37 methylene units. Compounds of the N₃-(CH₂)_<i>n</i>-COOMe type (denoted as az<i>n</i>ME) were synthesized with <i>n</i> = 5, 10, 15, 19, 28, 37 and studied using relaxation-assisted two-dimensional infrared spectroscopy. The speed of the ballistic transport, initiated by the N₃ tag excitation, increased ca. 3-fold for the longer chains (<i>n</i> = 19-37) compared to the shorter chains, from 14.7 to 48 Å/ps, in line with an earlier prediction (Nawagamuwage et al. 2021, <i>J. Phys. Chem. B</i>, <b>125</b>, 7546). Modeling, based on solving numerically the Liouville equation, was capable of reproducing the experimental data only if three wavepackets are included, involving CH₂ twisting (Tw), wagging (W), and rocking (Ro) chain bands. The approaches for designing molecular systems featuring a higher speed and efficiency of energy transport are discussed.