Theoretical modeling of defects in the molecular crystal of 2-(2'-hydroxyphenyl)benzothiazole
2-(2'-hydroxyphenyl)benzothiazole is a photoreactive compound that exhibits excited state intramolecular proton transfer in the structure with an OH...N hydrogen bond. Energy of various structures is calculated for isolated molecules, clusters and periodic structures of 2-(2'-hydroxyphenyl)benzothiazole by density-functional based tight-binding methods. It is shown that the most stable conformation of the isolated molecule is a planar structure with an OH...N hydrogen bond. Other conformations have significantly larger energy in comparison with the average room temperature heat energy that implies a low equilibrium number of those structures in non-polar solvents. In crystal the defect with lowest energy is non-hydrogen-bonded conformation formed by rotation of the OH bond. The energy of this defect is close to the energy difference for corresponding conformations of the isolated molecule. For other conformations, the energy values of the defects are larger than the energy differences for isolated molecules. In contrast to the crystal of 2-(2'-hydroxyphenyl)benzoxazole, energy of the defect caused by the entire molecule reorientation is comparable with the energy of defects caused by different conformations.