Aromatic rings in porphyrins and their naturally occurring derivatives are among the most important chemical individuals in the world: no aerobic life on this planet can do without the characteristic carbon- and nitrogen-based macrocycles, which carry oxygen in the bloodstream (as a part of hemoglobin) and allow plants to capture sunlight’s energy with their chloroplasts. Over the last decades the exceptional electron-transport and energy-harnessing capabilities of the macro- and polycyclic aromatic species have been utilized in cancer therapy, drug delivery, bio-imaging, molecular electronics, solar cells, lighter converters, bio-sensors, quantum computing, photoluminescent materials, photodetectors, and many, many others, making aromaticity one of the most commonly exploited theoretical concepts in chemistry – according to the ISI Web of Science, in 2018 there were about 45 papers published every day that contained the word aromatic (or its antithesis) in the title, keywords or abstract. On the other hand, the lack of a rigorous definition and the resulting superfluous diversity (dozens of types and rules of aromaticity) and numerous examples of the discrepancies between different aromaticity criteria proposed in the literature, have become the main reasons for this concept being perceived by some members of the chemical community as an elusive, questionable and suspicious concept. But, if rightly?
In this project we propose a profound paradigmatic change of the concept of aromaticity quantification to reveal its true colors and unearth its real predictive power. The long-term goal of this project is to understand how aromaticity and different resonance effects determine the physicochemical properties in such systems. In the first goal, we developed a novel computational method called the electron density of delocalized bonds (EDDB) that provides both a detailed description of local aromaticity of selected molecular fragments as well as the bird's-eye view on the global aromaticity of nanoscopic-size molecules and assemblies at a reasonable computational cost. The second research goal of the proposal was to use the EDDB method to gain insights into the mechanisms of the resonance-driven phenomena in the multifaceted aromatics that are instrumental in the design of new catalysts, spin-bearing materials, organic field-effect transistors, and many other.
