Metal ion coordination with an asymmetric fan-shaped dendrimer at the air-water interface.

Metal coordination to monolayers of 4-{10-[4-(3,5-bis-benzyloxy)-phenyl]-anthracen-9-yl}-benzoic acid ([G1-An]-CO(2)H, G1) and 4-(10-{4-[3,5-bis-(3,5-bis-benzyloxy)-benzyloxy]-phenyl}-anthracen-9-yl)-benzoic acid ([G2-An]-CO(2)H, G2) at the air-water interface and to Langmuir-Blodgett (LB) films was investigated using surface pressure-area isotherms, ultraviolet-visible (UV-vis) spectroscopy, atomic force microscopy (AFM), and X-ray reflectivity (XRR). Surface pressure-area isotherms show that G1 and G2 have different limiting areas according to the type of subphase. The limiting area of G1 and G2 increased more with Al(3+) than with Eu(3+) in the subphase. This result indicates that the hydrophilic core group is anchored to ions in the water via bidentate chelates with the carboxylate oxygen atoms of G1 and G2. Circular domains and aggregates were observed for the LB film. The different behavior of Eu(3+) and Al(3+) complexes is originated from the intrinsic nature of the ion, i.e., coordination number.