Electronic and optical properties of families of polycyclic aromatic hydrocarbons: a systematic (time-dependent) density functional theory study

TL;DR

This study systematically compares the electronic, optical, and transport properties of various polycyclic aromatic hydrocarbons using density functional theory, revealing trends related to molecular size and charge state relevant for organic opto-electronic applications.

Contribution

It provides a comprehensive DFT-based analysis of multiple PAH classes, highlighting their potential for opto-electronic devices and offering insights into their size-dependent properties.

Findings

Circumacenes exhibit superior transport properties.

Oligorylenes are highly efficient in low-energy photon absorption.

General trends of properties as a function of molecular size and charge are identified.

Abstract

Homologous classes of Polycyclic Aromatic Hydrocarbons (PAHs) in their crystalline state are among the most promising materials for organic opto-electronics. Following previous works on oligoacenes we present a systematic comparative study of the electronic, optical, and transport properties of oligoacenes, phenacenes, circumacenes, and oligorylenes. Using density functional theory (DFT) and time-dependent DFT we computed: (i) electron affinities and first ionization energies; (ii) quasiparticle correction to the highest occupied molecular orbital (HOMO)-lowest unoccupied molecular orbital (LUMO) gap; (iii) molecular reorganization energies; (iv) electronic absorption spectra of neutral and $\pm1$ charged systems. The excitonic effects are estimated by comparing the optical gap and the quasiparticle corrected HOMO-LUMO energy gap. For each molecular property computed, general trends as a function of molecular size and charge state are discussed. Overall, we find that circumacenes have the best transport properties, displaying a steeper decrease of the molecular reorganization energy at increasing sizes, while oligorylenes are much more efficient in absorbing low-energy photons in comparison to the other classes.