Concavity Effects on the Optical Properties of Aromatic Hydrocarbons

TL;DR

This study investigates how the shape and connectivity of curved aromatic hydrocarbons influence their optical properties, revealing shifts in optical absorption and the emergence of dark excitations, with implications for designing new molecular materials.

Contribution

It introduces a systematic analysis of concavity and cccccccccccccccccccccccccc and their effects on the optical properties of PAHs, supported by quantum chemistry calculations and experimental data.

Findings

Concavity and cccccccccccccccccccccccccc Shifted bright optical lines to higher energies.

Introduced symmetry-forbidden dark excitations at low energy.

Good agreement with experimental data.

Abstract

We study the modifications on the ground and excited state properties of polycyclic aromatic hydrocarbons (PAHs), induced by the variation of concavity and $\pi$-connectivity. Inspired by experimentally feasible systems, we study three series of PAHs, from H-saturated graphene flakes to geodesic buckybowls, related to the formation of fullerene C60 and C50-carbon nanotube caps. Working within the framework of quantum chemistry semi-empirical methods AM1 and ZINDO/S, we find that the interplay between concavity and \pi-connectivity shifts the bright optical lines to higher energies, and introduces symmetry-forbidden dark excitations at low energy. A generally good agreement with the available experimental data supports our results, which can be viewed as the basis for designing optical properties of novel curved aromatic molecules.