Concavity Effects on the Optical Properties of Aromatic Hydrocarbons

Caterina Cocchi, Deborah Prezzi, Alice Ruini, Marilia J. Caldas, Annalisa Fasolino, Elisa Molinari

Published 2013-06-12Version 1

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.