Significance of nuclear quantum effects in hydrogen bonded molecular chains

TL;DR

This paper investigates how nuclear quantum effects, especially proton tunneling, influence the structural, electronic, and mechanical properties of hydrogen-bonded molecular chains, revealing their critical role in material behavior.

Contribution

It demonstrates that nuclear quantum effects induce proton transfer and electron delocalization, significantly impacting the stability and electronic states of hydrogen-bonded molecular systems.

Findings

Proton transfer enhances electron delocalization along the chain.

Nuclear quantum effects increase the cohesive energy and stability.

New electronic in-gap states localized at chain ends are identified.

Abstract

In hydrogen bonded systems, nuclear quantum effects such as zero-point motion and tunneling can significantly affect their material properties through underlying physical and chemical processes. Presently, direct observation of the influence of nuclear quantum effects on the strength of hydrogen bonds with resulting structural and electronic implications remains elusive, leaving opportunities for deeper understanding to harness their fascinating properties. We studied hydrogen-bonded one-dimensional quinonediimine molecular networks which may adopt two isomeric electronic configurations via proton transfer. Herein, we demonstrate that concerted proton transfer promotes a delocalization of {\pi}-electrons along the molecular chain, which enhances the cohesive energy between molecular units, increasing the mechanical stability of the chain and giving rise to new electronic in-gap states localized at the ends. These findings demonstrate the identification of a new class of isomeric hydrogen bonded molecular systems where nuclear quantum effects play a dominant role in establishing their chemical and physical properties. We anticipate that this work will open new research directions towards the control of mechanical and electronic properties of low-dimensional molecular materials via concerted proton tunneling.