Berlin 2018 – scientific programme
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DS: Fachverband Dünne Schichten
DS 25: Organic Thin Films, Organic-Inorganic Interfaces: Session I (joint session DS/CPP)
DS 25.2: Talk
Wednesday, March 14, 2018, 16:45–17:00, H 0111
Synthesis and combined experimental and theoretical characterization of dihydro-tetraaza-acenes — •Bernd Kollmann1, Zhongrui Chen2, Daniel Lüftner1, Olivier Siri2, and Peter Puschnig1 — 1Institute of Physics, University of Graz, NAWI-Graz, Universitätsplatz 5. 8010 Graz, Austria — 2Aix Marseille Universite, CNRS, CINaM UMR 7325, 13288 Marseille, France
We present a combined experimental and theoretical study of electronic and optical properties of dihydro-tetraaza-acenes (DHTAn). Using a solvent-free condensation, we are able to synthesize DHTA5, DHTA6 and DHTA7 molecules. We investigate their gas-phase electronic structures of by means ab-initio density functional calculations employing an optimally-tuned range-separated hybrid functional. By comparing with the parent linear oligoacenes (nA) and based on computed ionization potentials and electron affinities, we predict DHTAn molecules to be more stable than acenes of the same length, where we expect DHTAn molecules to be persistent at least up to n = 7 rings. We further exploit the analogy with nA by analyzing the entire intramolecular π-band structure of the DHTAn molecules. This clearly reveals that the additional two electrons donated by the dihydropyrazine group are delocalized over the entire molecule and contribute to its π-electron system. As a consequence, the symmetry of the frontier orbitals of DHTAn differs from that of the parent nA molecule. This is also illustrated by the UV-vis absorption spectra which have been measured for DHTA5, 6 and 7 dissolved in dimethyl sulfoxide and analysed by means of excited state calculations with an time-dependent DFT framework.