A Renaissance of the (Anti)Aromaticity Concept in Modern Applications of Organic Chemistry

This dissertation focuses on applying computational quantum chemical tools to explore modern applications of aromaticity and antiaromaticity in organic chemistry. Even though all sophomore organic chemistry students learn about the concepts of aromaticity and antiaromaticity, these ideas continue to find exciting applications in active areas of research. The topics covered in this dissertation include understanding the effects of supramolecular self-assembly on the electronic properties of organic pigments and understanding the origin of acidity differences in popular photoacids. We found that organic pigments with bifunctional hydrogen bonding sites, such as indigo, isoindigo, diketopyrrolopyrrole, and naphthodipyrrolidone, can self-assemble through hydrogen bonding interactions, showing increased [4n] π-electron antiaromaticity and lower LUMO energy levels. The reciprocal relationship between hydrogen bonding and antiaromaticity gain makes them good candidates for components of n-type organic field-effect transistor (OFET) materials. We found that π-polarization of acridone compounds can perturb the numbers and positions of Clar sextet rings. Decreasing numbers of Clar sextets are connected to experimental observations of a narrowing HOMO-LUMO gap and increased charge mobility in hydrogen-bonded assemblies of quinacridone and epindolidione. We also found that many organic acids that are Hückel aromatic in the ground state can convert to Baird antiaromatic in the excited state, triggering facile proton transfer. Stronger photoacids show enhanced “antiaromaticity relief” upon releasing a proton. Together this series of works highlight examples of the underlying effects of (anti)aromaticity in organic chemistry and increase chemical understanding.