# Aromaticity switching by quantum tunnelling

## TL;DR

This paper shows how quantum tunnelling can switch aromaticity in certain molecules, even at near-zero temperatures.

## Contribution

The study reveals ultrafast carbon tunnelling in antiaromatic systems that can switch aromaticity or create quantum superpositions.

## Key findings

- Pentalene derivatives exhibit aromaticity switching via carbon tunnelling at near-absolute zero.
- Quantum superposition of aromatic and antiaromatic states is possible in a coherent tunnelling regime.
- Substituted derivatives show similar aromaticity switching behavior.

## Abstract

Antiaromatic π-conjugated systems provide a powerful framework for understanding ultrafast molecular rearrangements driven by quantum tunnelling over their degenerate double-well potential surfaces. Here, we explore with computational tools the π-bond-shifting automerization in the antiaromatic dinaphtho[2,1-a : 1,2-f]pentalene (1), dinaphtho[1,2-a : 2,1-f]pentalene (2), and a series of substituted derivatives. These molecules exhibit a distinctive feature: local aromatic and antiaromatic rings can interconvert their aromaticity character even close to the absolute zero via unusually fast carbon tunnelling. If these systems can be prepared in a coherent regime, the quantum superposition between the original states would delocalise their nuclear wavefunctions in a state that we describe as a “Schrödinger's aromaticity cat.”

Carbon tunnelling in pentalene-based polycyclic molecules enables ultrafast π-bond rearrangements switching local aromaticity/antiaromaticity, or leading to a quantum “Schrödinger's aromaticity cat” in a coherent tunnelling regime.