Modeling of a Tröger’s tweezer and its complexation properties

Molecular tweezers attracted attention because of their potential to selectively bind important chemicals, which can be utilized in medicine or in pollution treatment. In this study, the aromatic binding properties of a recently synthesized tweezer based on the Tröger’s base and its complex with nitrobenzene are investigated ab initio, using the DFT and MP2 computations. The predicted geometries and energies of the complex with nitrobenzene are well comparable with the experimental data. The B3LYP and BPW91 functionals did not provide a stable binding, in contrast to the observation. Only addition of the empirical Grimme correction for the van der Waals forces, not present in conventional DFT, yielded results consistent with the experiment, MP2 computations, and similar benchmark models. The correction also caused minor improvements of the Raman and infrared spectra, but not in the entire region of vibrational frequencies. The results suggest that the role of the electrostatic interaction in the investigated complex is minor and the interaction stabilization is driven by the contact area between the polarizable aromatic systems. The vdW-DFT method thus provides an efficient tool for the rational synthesis of the complexes.