Multifunctional Materials Based on Self Assembly of Molecular Nanostructures

摘要

In this program we developed an important class of multifunctional and self assembling materials based on the use of triblock molecular structures that had both luminescent chromophores and dipole moments. The objective was to integrate self assembly, encoded in the triblock structure, luminescent properties, and the properties characteristic of materials that have macroscopically polar structure. Our research over the past few years demonstrated self assembly in these materials with the formation of layered nanostructures measuring a few nanometers, and also photoluminescent behavior in the solid state of these materials. We also found these materials form thin films on substrates such as glass that exhibit spontaneous second harmonic generation when probed with infrared laser beams. An important milestone in the program was the discovery of piezoelectricity in the self assembling materials containing triblock molecules composed of oligostyrene, oligoisoprene, and biphenyl ester-phenylene vinylene blocks. The experiments were performed in a Nomarski interferometer, and a piezoelectric coefficient of 0.028 pm/volt was observed in thin films that were never exposed to an electric field. We concluded from this observation that the observed signal is the result of spontaneous polar organization by self assembly. The multifunctional materials were also found to have the unusual property of having almost identical absorption spectra in both dilute solution as well as the solid state with only a relatively small blue shift of 9 nm. A narrow red shifted emission was observed also which is not common in similar materials without self assembling properties. We believe this behavior is connected to the nanostructured nature of these materials. Finally, the program started an investigation of materials that could self assemble in aqueous media and were therefore designed to have amphiphilic nature.