Computational studies in organic chemistry: from metalloporphyrins to fullerenes
Dr. Tatyana E. Shubina (Computer-Chemie-Centrum and Interdisciplinary Center for Molecular Materials, Friedrich-Alexander-Univ. Erlangen-Nürnberg)

Computational chemistry has become an indispensable tool for studying properties of known and predicting them for new compounds as well as investigating reaction mechanisms. In this talk I will show few examples from our current work that demonstrate success and failure of traditionally used methods in describing interaction energies, electron affinities (EA), UV-Vis spectra.
For example, interaction of small molecules such as O₂, NO and CO with hemoglobin (Hb) and myoglobin (Mb) plays a central role in living cells and is important for the respiration and regulation processes. It is thus very important and challenging to understand and predict/reproduce binding energies of these ligands reliably by quantum-chemical calculations. Additionally, the accuracy of such calculations serves as a good benchmark for the modeling of similar bioinorganic processes. Despite the increasing number of theoretical studies on this topic, the results still remain inconsistent and somewhat puzzling.
On the other hand, porphyrins and related systems recently have found successful application as sensitizers for dye-sensitized solar cells (DSSC).
In this work, I present computational studies involving some of the metalloporphyrins that are relevant to bioinorganic processes and solar cells. An accurate description of metalloporphyrine molecules (electronic structure and optical properties) is discussed. The present investigation also explores the accuracy of several DFT methods and compares them to other wavefunction-based methods.
As the second example, fullerenes, and particularly C₆₀ that have found use as organic n-type semiconductors in electronic devices, are discussed. Recenty,[1] it was shown that a self-organized layer (SAM) of substituted-fullerenes that combine the dielectric and the semiconductor functionalities in a single molecule can be used in the low-voltage organic field-effect transistors (FETs). Analysis of semiempirical molecular orbital calculations on such SAMs revealed deep electron traps in the interstitial volumes between adjacent fullerenes in the semiconductor layer. We therefore investigated the one- and two-electron reduced forms of the C₆₀-dimer, -trimer and –tetramer using DFT, HF-DFT and post-HF methods. This work reports results on stability of such dimers, their properties, spin-states crossings and electron transfers.

[1] C. M. Jäger, T. Schmaltz, M. Novak, A. Khassanov, A. Vorobiev, M. Hennemann, A. Krause, H. Dietrich, D. Zahn, A. Hirsch, M. Halik and T. Clark, J. Am. Chem. Soc., 135, 4893-4900 (2013).