Helical Poly(Phenyl Isocyanide) Based Conjugated Polymers: Synthesis, Structure Regulation, And Application

Herein, two kinds of poly(phenyl isocyanide) (PPI) based conjugated polymers were designed and synthesized. The first kind was tetraphenylethene (TPE) functionalized linear poly(TPE-NC)n and four-armed TPE-[poly-(TPE-NC)m]4 conjugated poly(phenyl isocyanide). In this work, TPE functionalized phenyl isocyanide (PI) monomers (TPE-NC) and TPE-based Pd(II) catalysts (TPE-Cat.a and TPE-Cat.b) were first synthesized, all of them were aggregation enhenced emission (AEE) active. The corresponding linear poly(TPE-NC)n and four-armed TPE-[poly-(TPE-NC)m]4 with controlled molecular weights, narrow molecular weight distributions, tunable structures were subsequently prepared through the living polymerization of TPE-NC with TPE-Cat.a or TPE-Cat.b in THF, respectively. Atomic force microscopy (AFM) and scanning electron microscopy (SEM) were used to investigate the self-assemble structures of the PPI in different solvents due to the unique helical structure of them. Stable helical assemblies could be formed by poly(TPE-NC)n at high concentration conditions while four-armed TPE-[poly(TPE-NC)m]4 could self-assemble into an apparent bumpy "caterpillar" like assembly. The introduction of TPE unit provided the PPI with excellent thermal stability, but their optical properties showed the typical phenomenon of aggregation-caused quenching (ACQ), which were opposite to the small molecules. These properties also made the PPI to generate a vapochromism phenomenon and accomplish the detection of volatile organic compounds. Moreover, these conjugated polymers could act as good dispersants for carbon agglomerates in poor solvents.The other kind was thiol groups functionalized poly(4-isocyano benzoic acid/ pyridine-4-thiol)-b-poly(3-hexylthiophene) (PPI(-SH)-b-P3HT) conjugated copolymers. The PPI(-SH)-b-P3HT conjugated polymers were synthesized through hydrogen bonding induced micellization and subsequent thiol-disulfide exchange reaction. The assembly of PPI(-SH)-b-P3HT and gold nanoparticles (Au NPs) was spontaneously occurred by taking advantage of the formation of Au-S bond at chloroform/water interface, leading to a separated composite film. Transmission electron microscopic (TEM) and AFM observations showed the film had a highly ordered architecture with tunable Au NPs density, depending on the initial concentration of Au NPs. Interestingly, the film substrate exhibited a strongly Au NPs concentration dependent surface enhanced Raman scattering (SERS) activity, which were sensitive to the kinds and concentrations of target analytes in the SERS measurement.