Layer-by-layer assembly of a new L-glutamic acid based polymer with PAH: formation of hollow sphere during deposition, dye loading and chiroptical switch

A new polymer with acryl backbone and L-glutamic acid (PAGlu) as the side chain was synthesized and their assembly with cationic poly(allylamine hydrochloride) (PAH) through a layer-by-layer technique was investigated. Although PAGlu dissolved in water showed no particular organized structures, it formed hollow spheres when assembling with PAH. Both SEM and TEM observation for the deposited films confirmed the hollow structure. Furthermore, observation by SEM for each deposition revealed that the hollow structure was formed during the layer-by-layer assembly process. Differently from that of the hollow capsules formed from template nanoparticles, this method provided directly the hollow structure without any template. Moreover, the water-insoluble LbL film with the hollow structure showed a rapid loading and release of dye molecules such as TMPyP (5,10,15,20-tetrakis(4-N-methylpyridyl)porphinetetra(p-toluenesulfonate)). Due to the chiral nature of the PAGlu, the loaded dye molecule showed induced chirality owing to the interaction with the L-glutamic acid moiety. In addition, this dye-loaded film can show a reversible color and chirality change upon alternative exposure to HCl and NH3 gases, realizing a gas sensing chiroptical switch.