An amphiphilic barbituric acid derivative was found to form stable monolayers showing a clear phase transition at the air/water interface. It is interesting to find that the deposited Langmuir-Blodgett (LB) films of the compound showed circular dichroism (CD) although the molecule itself was achiral. AFM measurements on the transferred one-layer LB film revealed that spiral nanoarchitectures were formed. It was further found that the supramolecular chirality of the LB films was related to symmetry breaking at the interface. Hydrogen bonding and the pi-pi stacking between the neighboring molecules resulted in chiral fibers which formed the spiral structures. To the best of our knowledge, this is the first report on the chirality of the molecular assemblies and spiral nanostructures formed through the air/water interface by achiral molecules.

Some novel properties of organized molecular films of 10,12-tricosadiynoic acid (TDA), which were modulated by transition metal ions, were investigated. It was found that metal ions such as Cu(2+), Zn(2+), Ni(2+), Cd(2+), and Ag(+) in the subphase can greatly affect the monolayer formation of TDA and the properties of the subsequently deposited Langmuir-Blodgett (LB) films, particularly in the case of Ag(+), Zn(2+), and Cu(2+) ions. TDA LB film from the subphase containing Ag(+) ion could not be photopolymerized. It was suggested that both the strong chelating property to the carboxylate and the easy reduction of Ag(+) in the film disrupted the topochemical sequence of TDA and resulted in no polymerization in the film. Zinc ion coordinated TDA film could be photopolymerized into a blue polydiacetylene (PDA) film, which showed a reversible thermochromism between blue and purple color upon thermal stimulation. Fourier transform infrared spectra revealed the difference of the Zn(2+)-PDA film from those of the other ions, and the mechanism of the thermochromism was discussed. Copper ion coordinated TDA film could only be photopolymerized to a red PDA film, which showed supramolecular chirality although TDA itself was achiral. Atomic force microscopic measurements revealed the nanofiber structure in the Cu(2+)-PDA film. The supramolecular chirality of the Cu(2+)-PDA film was suggested to be due to the arrangement of the polymer backbone in a helical sense. Furthermore, it was found that the chiral assemblies from the achiral TDA molecules were very stable and the chirality could be kept even upon heating or treating with alkaline solution. While many synthetic efforts have been devoted to the functionalization of PDA films, we provided a simple method of modulating the organization and function of PDA films through metal ions.

The aggregation and induced chirality of an anionic meso-tetraphenylsulfonato porphyrin (TPPS) on a layerby-layer assembled deoxyribonucleic acid/poly(allylamine hydrochloride) (DNA/PAH) film were investigated. It was found that TPPS could directly penetrate into a DNA/PAH film and be assembled into both H-aggregates and J-aggregates. Both of the aggregates showed strong induced circular dichroism (CD) in the film. On the other hand, TPPS could also penetrate into the DNA/PAH film through the help of a cationic meso-tetrakis-(4-N-methylpyridyl) porphyrin (TMPyP), as a spacer. In this case, J-aggregates formed in the DNA/PAH matrix and induced chirality was also observed. The induced chirality of the TPPS J-aggregate followed the DNA chirality, in the presence of TMPyP; however, an opposite induced chirality was observed in the absence of TMPyP. Atomic force microscopy images showed nanorods on the surface of DNA layer in both cases, which were composed of H-type and/or J-type aggregates of TPPS. The mechanism of the formation of the opposite induced CD signals was discussed.