Significance of nuclear quantum effects in hydrogen bonded molecular chains

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 π-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.

Significance Of Nuclear Quantum Effects In Hydrogen Bonded Molecular Chains

“…Computational resources were provided by the CESNET LM2015042 and the CERIT Scientific Cloud LM2015085, provided under the programme “Projects of Large Research, Development, and Innovations Infrastructures”. The manuscript has been previously submitted to the preprint server …”

Nuclear quantum effects made accessible: local-density fitting in multicomponent methods

“…Experimental and computational studies of the Quinonediimine chain were carried out by A. Cahlík et al. 29 A combination of scanning probe microscopy experiments and path integral molecular dynamics (PIMD) elucidated the complex interplay of nuclear quantum effects in hydrogen bonds on the chemical and physical properties of the chain. While in a canted ge-ometry of the chain the protons are localised, they identified a second form of a straight chain where the protons are delocalized.…”

“…Our first test system is a two-dimensional network of quinonediimine molecules, where NQEs visibly impact the structure and are relevant for the development of new engineered materials in the future. 29 The second example is a DNA fragment build from guanine-cytosine base pairs, unarguably one of the most important molecules from biochemistry. 30,31 It should be noted that in the following calculations we only compare local (LDF) to conventional (DF) implementations, as integral-direct calculations would be prohibitively expensive.…”