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 2020 (until September) there were about 43 papers published every day that contained the word 'aromatic' (or its antithesis) in 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 (anti)aromaticity, to reveal its true colors and unearth its real predictive power. Project hypotheses:
- Chemical resonance underlying electron delocalization is essentially of information-entropic nature: the key effect of the interference of different resonance forms is that we lose information on the assignment of electrons to particular bonds,
- One of the most distinguished features of aromatic compounds is their capacity to counterbalance 'destructive' effects of the electron excitations on the ground-state system of π-conjugated bonds by redistribution of the resonance forms in such a way that maximizes the resonance-entropy production or at least minimizes the resonance-entropy loss to preserve as much information contained in their π-systems as possible.
In this context of project hypotheses, the core objective of the project is to decipher information contained in the ground-state wavefunctions of selected topologically diversified aromatic molecules and underlying their unique physico-chemical properties, and to progress toward understanding of the first-principle rules that determine evolution of this information in the lowest-lying excited states, under the influence of external magnetic field as well as along chemical reactions.
All the research tasks in this project are organized in such a way that they enable validation of the project hypotheses gradually by providing answers to the following scientific questions:
(1) How to extract from the molecular wavefunction the information about assignments of electrons into particular bonds, and how to translate this information into the 'chemical language'?
(2) Is it possible to prove experimentally that the source of the chemical resonance is indeed of entropic nature?
(3) Why the currently used theoretical methods fail to provide a consistent and reliable description of the interplay between chemical resonance and the magnetic-response properties of the expanded porphyrins and PAHs?
(4) Is it possible to construct the lowest-lying excited singlet states from the ground-state wavefunction without explicit solving of the time-dependent Schrodinger equation, and what are the limits of the MIEP applicability?
(5) How can we use the resonance-entropy concept and MIEP in the design of emitters exhibiting thermally activated delayed fluorescence (TADF)
(6) and as a rationale for singlet fission chromophore design?
Thus, verification of project hypotheses requires cross-disciplinary approaches using knowledge from mathematics (probability and information theory), theoretical and computational chemistry, physics, and materials science, which makes it truly exciting multidisciplinary challenge. To make sure that all the key aspects of the project can be tackled within the foreseen time a team consisting of PI, 2 PhD and 3 MSc students will be composed. To guarantee the best expertise and resources available most of the research tasks will be carried out in close collaboration with the world-renowned experts (theoreticians and experimentalists) in the field of molecular aromaticity and materials science from China, USA, UK, Spain, and Sweden. All the research tasks in this proposal will be carried out with partial support of the PL-Grid Infrastructure (Poland), BSC-CNS (Spain), CSD3 (UK), and resources provided by Jagiellonian University and University of Girona. The most demanding high-level calculations will be performed using the purchased workstations with unique specifications. The state-of-the-art computational methods and experimental techniques will be used.
Validation of the maximum information-entropy principle for electronic transitions in aromatic molecules would potentially have far-reaching implications for predictive computational chemistry as well as organic chemistry in general
. The results of the project will hopefully provide the basis for an updated and more comprehensive IUPAC definitions of the concepts of aromaticity (antiaromaticity), olefinicity, aliphaticity, etc. The project will also deliver a novel methodology, software tools and research-based knowledge that in the future could support the design of modern spin-bearing compounds, organic fields-effect transistors, resonance-driven optical-mechanistic switches, dye-lasers, solar collectors, and many others. A tangible result of the research project will be scientific papers published in reputed journals from the ISI Master Journal List.