Thin films of organic semiconductors have a wide application in modern electronic devices. Until now we have used base surfaces for organic molecular beam epitaxy (OMBE) [1] provided by b-alanine crystal cleavage along (010) surfaces. Having a stake in different types and symmetries of base surfaces, we searched through the Cambridge Structural Database (release 5.35, nov 2013) by means of the ToposPro program package [2] modified with specially tailored procedure that determines possibility of the crystal to cleave along given surface. This procedure is based on the analysis of the share of intermolecular interaction energy of molecules within the layer comparing to the total energy of interaction.
As a result, we have extracted 5203 monomolecular structures with 2-periodic hydrogen bonded network as the most probable candidates in easily cleavable crystals. We rejected the structures of solvates and hydrates as inappropriate in order to guarantee stability to ultra-high vacuum conditions needed for OMBE. Also we did not consider salts because of inability to use AA-CLP force field [3] for computation of interaction energies in ionic compounds. Additionally, for some key structures we calculated intermolecular interaction energies by means of the more accurate PIXEL method [4] trying to establish the structural features that can lead to the ability of molecular crystals to cleave.
The work was supported by the Russian government (Grant 14.B25.31.0005).
Figure 1. The hydrogen bond network in a b-alanine crystal built of zwitter-ionic dimers.
References
[1] S. Trabattoni, M. Moret, M. Campione, L. Raimondo, A. Sassella Cryst. Growth Des. 2013, 13, 4268.
[2] V.A. Blatov, A.P. Shevchenko, D.M. Proserpio Cryst. Growth Des. 2014, 14, 3576
[3] A. Gavezzotti New J. Chem. 2011, 35, 1360.
[4] A. Gavezzotti J. Phys. Chem. 2002, 106, 4145; A. Gavezzotti J. Phys. Chem. 2003, 107, 2344.