99 Semesters of Chemistry - A Personal Retrospective on the Molecular State Approach by Preparative Chemists

Molecular states are the real building blocks of the chemist, because the structure of a molecule can change considerably as its energy and thus its electron distribution varies within the time-domain of dynamic relaxation. The ever increasing use of measuring methods from the armory of physics to characterize molecules by their molecular state fingerprints and, above all, of computers to rationalize both their properties and their microscopic reaction pathways, provides a wealth of information for the development of chemistry. To deal with the complexity of molecular states, a qualitative model based on the topology and symmetry of their structures as well as of their energies resulting from the electron distribution over the respective effective nuclear potentials is presented and is illustrated by examples of our own efforts to elucidate molecular state properties including time-dependent dynamics, microscopic reaction pathways both in the gas phase and in solution, and the self-assembly of molecules on crystallization. In conclusion, a personal retrospective is summarized and some prospects for the future are outlined.