Ask Not How Many, But Where They Are: Substituents Control Energetic Ordering of Frontier Orbitals/Electronic Structures in Isomeric Methoxy-Substituted Dibenzochrysenes

Abstract

Redox properties of polycyclic aromatic hydrocarbons (PAHs) can be modulated by substitution with electron-rich groups. Here we show, using the example of dibenzo­[g,p]­chrysene (DBC), that substitution <i>position</i> (i.e., <i>meta</i> vs <i>para</i>) alters the energetic ordering of frontier molecular orbitals (FMOs), leading to cation radicals with altered electronic structures and thereby redox/optical properties. In particular, incorporation of four methoxy groups in parent DBC at <i>meta</i> positions similarly impacts the energies of phenanthrene-like HOMO and biphenyl-like HOMO-1, while their incorporation at <i>para</i> position swaps energetic ordering of HOMO and HOMO-1. We demonstrate that a straightforward analysis of FMOs provides valuable insight toward the rational design of novel PAHs with tailored redox properties