Self-Organization of Four Symmetric Tri-phenyl-benzene Derivatives

The self-assembly of four symmetrically substituted tri-aryl-benzene derivatives of formula C 24 H 15 X 3, 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···Cl and C−H···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 π−π 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.