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Mauro Causa'

Deparment of Chemical and Materials Engineering, Universita' di Napoli "Federico II"

Maximum Probability Domains in molecular crystals and surfaces

The Maximum Probability Domain (MPD) analysis due to Andreas Savin is applyed to molecular crystals and their surfaces. The correlation effects are included using Quantum Monte Carlo techniques. The MPD correlated method will be applied to rare gas solids, organic materials applied in photo-electronics, and to crystal phases relevant in heterogeneous atmospheric chemistry.

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Piotr Kasprzycki

Institute of Experimental Physics, Faculty of Physics, University of Warsaw, ul. Hoza 69, 00-681 Warsaw, Poland

The correlation between the proton transfer time and electron density in the inner cavity of porphycenes

Numerical solutions of the Schrödinger equation can nowadays be obtained for reasonably large organic and organometallic molecules with useful accuracy using approximate ab initio or DFT methods. These approximate solutions are also available for porphycene which is an important chromophore [1]. Porphycene and its derivatives show useful properties for material sciences and are also considered excellent photosensitive media for applications in photodynamical therapy of cancer [2]. Several papers have discussed the energy structure and dynamic aspects of hydrogen transfer in this systems [4, 5]. We report on the results of NCI analysis - theoretical tool based on Bader approach [6] - performed for symmetrically and asymmetrically substituted porphycene derivatives. We have carried out DFT calculations at the level B3LYP/6-311(d,p) of theory. These calculations were followed by NCI analysis. Calculations showed a correlation between the value of electron density gradient localized between nitrogen and hydrogen atoms in the inner cavity of a molecule and the time of the proton transfer in the examined systems. Proton transfer times were obtained in a femtosecond transient absorption anisotropy experiment, which is a polarisation-sensitive variant of an ultrafast pump-probe technique. Double hydrogen transfer leads to the change of transition dipole moment directions - transition moment of chemically identical tautomerization product forms an angle of α = (72±2)◦ with that of initially excited form. This change is manifested as variation in transmitted light intensity measured in two orthogonal polarizations. Under appropriate conditions, rise/decay times of anisotropy reflect the kinetics of double hydrogen transfer. We show that quantum theory of atoms in molecules (QTAIM) based on Bader approach is useful not only for detection of covalent bond but also for hydrogen bonds and weak van der Waals interaction. NCI analysis provides the possibility to compare strength of hydrogen bonds in porphycene derivatives, which allows one to predict the proton transfer time for new molecules. Additionally, these approach have helped us to design structure of a derivative with the proton transfer time of the order of tens of picoseconds. Furthermore, substitution in 2,7 and in 10,19 position of porphycene can induce differentiation of hydrogen bonds. The effect is especially evident in the case of 10,19-di-methylporphycene (2MPc) and 2,7-di-t-buthylporphycene (DTBP). This behavior may be the result of asymmetric distribution of electron density in the center of the molecule. This fact can be significant for understanding the mechanism of double hydrogen transfer between inner nitrogen atoms.

References

[1] D. Sanchez-Garcia, J. L. Sessler, Chem. Soc. Rev., 37, 215, (2008). [2] J. C. Stockert, M. Canete, A. Juarranz, A. Villanueva, R. W. Horobin, J. I. Borrell, J. Teixido, S. Nonell, Curr. Med. Chem., 14, 997, (2007) . [4] Ł. Walewski, J. Waluk, B. Lesyng, J. Phys. Chem. A., 114, 2313–2318, (2010). [5] M. Gil, J. Waluk J. Am. Chem. Soc. 5, 129, (2007). [6] E. R. Johnson, S. Keinan, , J. Contreras-García, R. Chaudret, J-P Piquemal, D. Beratant, W. Yang, J. Chem. Theo. and Comp., 25, (2011).

Slawomir J. Grabowski

Faculty of Chemistry, University of the Basque Country UPV/EHU, and Donostia International Physics Center (DIPC),P.K. 1072, 20080 Donostia, Spain IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain

Non-covalent interactions: characteristics and mechanisms of formation - the topological approach

Numerous non-covalent interactions are characterized by the electron charge transfer from the Lewis base unit to the Lewis acid [1]. This is connected with the other processes reflected by the change of geometrical, energetic and topological parameters. For example, different characteristics of the hydrogen bond and various criteria of the existence of this interaction were discussed in the literature [2]. One can mention the topological criteria of Koch and Popelier [3,4]. On the other hand, the hydrogen bond mechanism was discussed in terms of NBO method [5]. Very recently it was found that the hydrogen bond, the halogen bond and other non-covalent interactions are steered by the same processes [6]. This is reflected by the same changes of parameters. For example, the A-H...B hydrogen bond formation is connected with the increase of the positive charge of H-atom and the decrease of its volume. The same changes are observed for X-halogen atom in the A-X...B halogen bond. Various similarities and differences between numerous non-covalent interactions may be discussed.

References

[1] Lipkowski, P.; Grabowski, S. J.; Leszczynski, J. J. Phys. Chem. A 2006, 110, 10296–10302. [2] Grabowski, S.J. Chem.Rev. 2011, 11, 2597-2625. [3] Koch, U.; Popelier, P.L.A. J.Phys.Chem. 1995, 99, 9747-9754. [4] Popelier, P. Atoms in Molecules. An Introduction, Prentice Hall, Pearson Education Limited 2000. [5] Alabugin, I.V.; Manoharan, M.; Peabody, S.; Weinhold, F. J.Am.Chem.Soc. 2003, 125, 5973-5987. [6] Grabowski, S.J. Phys.Chem.Chem.Phys. accepted

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