Amphiphilic conjugated dendritic macromolecules by molecular engineering: Properties and applications

We have synthesized a class of new dendritic materials consisting of hydrophobic oligo(p-phenylene vinylene) core branches and hydrophilic oligo(ethylene oxide) terminal chains. Due to the amphiphilic properties arising from the large difference in solubility between the two constituent components, unique concentration-dependent, photo-physical and temperature-responsive properties were observed for these dendritic macromolecules. The critical micelle concentration (CMC), solvatochromic properties and lower critical solution temperature (LCST) behavior are the most outstanding properties obtained from these novel amphiphilic conjugated dendritic macromolecules. These stimuli-responsive properties are quite sensitive and controllable by changing the branch number and the ratio of the hydrophilic oligo(ethylene oxide) to hydrophobic oligo(p-phenylene vinylene) moieties.; Many interesting applications in various areas also have been developed base on their unique properties. First of all, the efficient energy transfer between new dendrimers in aqueous medium can be acheved, because the energy level of donors and acceptor was suitable for energy transfer and they can be located very closely in micellar structure. The higher Stern-Volmer constants (KSV) for energy transfer obtained from suitable combination of donor and accepter. Furthermore, the formation of various sizes and shapes of gold particles and their fiber like self-assembled structures also can be observed, when the light was irradiated to the mixture of suitable gold salts and appropriate novel macromolecules in aqueous medium. The main reaction of this process is the singlet oxygen meditated photo-oxidation of dendrimers. Novel amphpiphilic dendrimers can act not only reducing agents but also the protecting agents for stabilizing/self-assembling of the resultant gold nanoparticles. Finally, the strong interactions between one of our novel maromolecules ( RD) and single wall carbon nanotubes (SWNTs) via pi-pi stacking forces between conjugated core units in RD and the flat graphite structures of SWNTs were observed, which resulted in the enhanced solubility of SWNTs in aqueous medium with RD. One more noticeable feature of this study is the surface-bonded RD can be replaced by other amphiphiles ranged from conventional surfactants like sodium dodecylbenzene sulfonate (SDBS) and sodium dodecylsulfate (SDS) to biomolecules like lysophopholipids, which are supposed to have stronger interaction with SWNTs. As a result of exchange reaction, the enhanced fluorescent from detached RD was obtained.; As illustrated above, as synthesized a class of amphiphilic conjugated dendritic macromolecules possessed many interesting properties including temperature and concentration dependent phase transition behavior, photosensitivity and high affinity to SWNTs. Thus, these molecules could be used in a wide range of applications like controlled fabricate (via micellization in selective solvents or self-assembling), biosensors and multifunctional nanocomposites with various nanomaterials (e.g. metal nanoparticles, carbon nanotubes) for advanced optoelectronic systems, whose performance can be tuned in response to an external stimulus (e.g. temperature, pH).