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

TL;DR

This study demonstrates that long alkyl chains can facilitate ballistic energy transport at speeds up to 48 Å/ps, with experimental and modeling results showing increased efficiency in longer chains, advancing molecular energy transfer understanding.

Contribution

It introduces a new experimental and modeling approach to measure and understand ballistic energy transport in long alkyl chains, revealing a significant speed increase with chain length.

Findings

Transport speed increases with chain length, reaching 48 Å/ps for n=37.

Modeling requires three wavepackets: twisting, wagging, and rocking.

Experimental results align with previous predictions for longer chains.

Abstract

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)n-COOMe type (denoted as aznME) were synthesized with n = 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 (n = 19-37) compared to the shorter chains, from 14.7 {\AA}/ps to 48 {\AA}/ps, in line with an earlier prediction (Nawagamuwage et al. 2021, J. Phys. Chem. B, 125, 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 higher speed and efficiency of energy transport are discussed.