Growth-induced polarity formation in two-component crystals of organic molecules: A statistical analysis Original Research Article

On the basis of a layer-by-layer growth model, growth-induced polarity formation is investigated in two-component crystals (solid solutions) of polar HH (host) and non-polar GG (guest) or polar HH and GG molecules, with native HH and GG crystals being assumed centrosymmetric. These two types of chemical systems are compared with one another in terms of a statistical analysis being comprised by an investigation of polarity for a large number of molecular interaction energies chosen randomly within an assumed but realistic parameter space for energies. The study focuses on a statistical estimate of the potentiality of each type of chemical system to evolve macroscopic polarity. Results are obtained by means of Monte Carlo simulations. Regardless of the type of GG molecules (non-polar or polar), solid solution formation significantly increases the probability to obtain polarity in comparison with single-component crystals of polar HH molecules only. However, a very high degree of vectorial alignment of polar molecules is only likely for ordered structures HGHG, but not for statistically uncorrelated distributions of HH and GG molecules as in real solid solutions. Within the scope of the present description, polarity formation is governed mainly by longitudinal interactions in systems with non-polar GG molecules, whereas it is also strongly influenced by lateral interactions in systems with polar GG molecules.