Self-organization of four symmetric tri-phenyl-benzene derivatives

The self-assembly of four symmetrically substituted tri-aryl-benzene derivatives of formula C24H15X3, where X = H (1), Cl (2), COOMe (3), and COOH (4), was studied as a function of the substituent X. Crystal packing analysis of compounds 1-3 showed that in 1, there are no strong face-to-face stacking interactions, whereas in both compounds 2 and 3, molecular columns were formed, held by numerous lateral C-H center dot center dot center dot Cl and C-H center dot center dot center dot O hydrogen bonds, respectively. However, strong intermolecular face-to-face aromatic interactions, appropriate for excimer formation, were observed only in 3, in line with results obtained by fluorescence spectroscopy. The pi-pi aromatic interactions are significantly stronger in the case of the triacid 4, but a lack of adequate single crystals of this compound prevented any detailed study for correlating crystal architecture with fluorescence emission observed. However, FT-IR and TEM experiments showed the existence of dimeric H-bonds and short (0.35 nm) distances between the phenyl rings.