π-π interaction of quinacridone derivatives.

The π–π stacking interactions play an important role in molecular assemblies of quinacridone derivatives (QAs). In our previous work (Sun et al., J Phys Chem A 2008, 112, 11382), we have shown that quinacridone derivatives can be self-associated as dimers in solution by means of NMR study. Herein, we perform theoretical studies on the molecular interaction in the dimers of QAs to illustrate π–π interactions in terms of their strength, geometrical preference, substituent effect, and physical nature. Density functional theory (DFT-D) was adopted to calculate potential energy surfaces. The detailed analysis on the intermolecular interaction in diversity of dimeric configurations reveals that the displaced conformations with specific geometries in both parallel and antiparallel stacking manners can be stabilized, which are in agreement with NMR experimental findings. 2011 Wiley Periodicals, Inc.