Faculty of Natural Sciences University of Matej Bel

Charge-transfer complexes

For a long time the main interest in chemistry was mainly focused on processes of creation and breaking of chemical bonds - chemical reactions. The last decades of modern research has shown that for proper description of various molecules in living organisms one needs to use more subtle mechanisms of interaction.

For example, the mechanism of action of many drugs in human body does not involve creation of chemical bonds with the target receptor, but arises from weak, non-bonding interactions (which in practice means also reversible bonding).

Figure 1 Mapped electrostatic potential for a) complex between benzene and TCNE, b) recently prepared complex with the donor (center) and acceptors (the edges) linked by aliphatic bridge in one molecule.

Figure 1 Mapped electrostatic potential for a) complex between benzene and TCNE, b) recently prepared complex with the donor (center) and acceptors (the edges) linked by aliphatic bridge in one molecule.

Charge transfer (CT) complexes consist of two or more organic molecules, one of which is electron acceptor and the second electron donor (Figure 1). CT complexes are characterized by electronic transition to an excited state in which there is a partial transfer of electronic charge from the donor to the acceptor moiety, manifested in typically coloured solutions of these complexes (Figure 2).

Figure 2 Complexes between methylated benzenes and TCNQ (tetracyanoquinodimethane) in chloroform

Figure 2 Complexes between methylated benzenes and TCNQ (tetracyanoquinodimethane) in chloroform

Our research is oriented on studying processes of CT complex formation, their properties, excited states as well as impact of different solvent environments by using modern approaches of computational chemistry including MP2, CCSD(T) and DFT methods. For example, charge transfer interactions in complexes between one of the strongest organic acceptor TCNE (tetracyanoethylene) and several donors - especially methyl substituted benzenes (Figure 1) have been studied in our group. For these donor molecules the ionization energy decreases with the increasing number of methyl groups, i.e. the donor strength increases. Calculations are typically performed using the computer cluster in High Performance Computing Centre (HPCC, Figure 3).

Figure 3 HPCC in Banská Bystrica

Figure 3 HPCC in Banská Bystrica

Selected publications

1. KYSEĽ, O., BUDZÁK, Š., MEDVEĎ, M., MACH, P.: MP2, DFT-D, and PCM study of the HMB-TCNE Complex: Thermodynamics, Electric Properties, and Solvent Effects. In International Journal of Quantum Chemistry, 2008, vol. 108, issue 9, p. 1533-1545.
2. KYSEĽ, O., BUDZÁK, Š., MACH, P., MEDVEĎ, M.: MP2 and DFT study of IR spectra of TCNE-methylsubstituted benzene complexes: Is charge transfer important? In International Journal of Quantum Chemistry, 2010, vol.110, iss. 9, p. 1712-1728.
3. MACH, P., BUDZÁK, Š., MEDVEĎ, M., KYSEĽ, O.: Theoretical analysis of charge-transfer electronic spectra of methylated benzenes – TCNE complexes including solvent effects: Approaching experiment. In Theoretical Chemistry Accounts, vol. 131, p. 1268 -1282.
4. MACH, P., JUHÁSZ, G., KYSEĽ, O.: Theoretical study of electronic absorptions in aminopyridines - TCNE CT complexes by quantum chemical methods, including solvent. In Journal of Molecular Modeling, Doi 10.1007/s00894-012-1437-9.


Faculty of Natural Sciences University of Matej Bel