Patrick Horst Strebert

• Despite their “weak nature” London dispersion interactions are omnipresent and of fundamental importance for many aspects of chemistry and biology and have often been underestimated in the description of intra- and intermolecular interactions. In this thesis, London dispersion is investigated in the gas phase with molecular beam experiments and quantum chemistry. The focus of this work lies in the investigation of London dispersion in the electronic ground state and the electronically excited state. For the electronic ground state, dispersion-bound dimers of triphenylmethane derivatives were analyzed. Depending on the dispersion energy donor, a tail-to-tail (TPM), head-to-tail (iPrTPM) or head-to-head (tBuTPM) arrangement can be assumed for the minimum structure. The tBuTPM dimer exhibits an exceptionally small C-H·· H-C contact which is stabilized by strong London dispersion interactions which was quantified by energy composition analysis. For the characterization of the dimer, the calculation of anharmonic frequencies was of high importance and was also validated with literature data. The second system, the chromone-MeOH balance represents an ideal molecular balance with two competing docking sites at the carbonyl oxygen. The experimental results are compared to theoretical predictions obtained from (TD)DFT-, DLPNO-CCSD(T) and SAPT-calculations to study the balance between electrostatics, induction and dispersion interaction in the S0 and T1 state. The chromone-solvent system was identified as an ideal system for studying London dispersion in multiple electonic states. Furthermore, candidates for derivivatives of chromone were analyzed with quantum chemical methods in the electronic ground and electronically excited state in an attempt to identify suitable candidates for further experiments. The 6-methylchromone shows promising behavior in stabilizing the inside pocket regardless of the electronic state and was analyzed in more detail with a variety of methods. Similar analysis of 2-CF3chromone and the 2-CF3, 6-methylchromone showed no special effect of a substitution in 2-position or possible cooperative effects.