Design,Synthesis And Application Of Functional Polyphenylenes

Light-emitting conjugated polymers(LCPs),especially ?-conjugated polymers(?-CPs)have received extensive attention from both industrial and fundamental research due to their excellent intrinsic one-dimensional orientation,long-range ?-conjugated system and structural stability.LCPs have promising applications in organic light emitting diode(OLED),field effect transistors,photovoltaic cells and bio/chemical sensors.In the midst of the broad sea of ?-CPs,polyphenylenes,particularly poly(p-phenylene)(PPP),are the simplest molecules,which could be utilized for fluorescence.However,there are some problems such as complicated synthetic method,severe synthetic conditions,poor thermal and optical stability,short fluorescence life,fluorescence quenching and so on,which hinder its application of photoelectric devices.Here,different from typical synthesis method adding flexible,soluble function groups in side-chain,a series of unsubstituted polyphenylenes which exhibit multi-colored fluorescence emissions(from 475?386 nm),excellent stabilities and high fluorescence quantum efficiencies(up to 70%)are designed and facilely synthesized under mild conditions in aqueous solutions.Detailed structural and optical characterizations and theoretical investigations reveal that the improvement of the optical behavior of polyphenylene molecules are predominantly induced by the induction of meta-phenylene units,which further caused the reduction of ?-electrons delocalization and interchain ?-? stacking.Meanwhile,modifying electron donor on the end of PHMP can also obtain a conjugated polymer which exhibit red-shift behavior of PL emission(from 444 nm to 475 nm).Elastic films with high fluorescent performances are further obtained by encapsulating the polyphenylenes with flexible polymers(PVP and PEG),forming insulated molecular wires.Furthermore,when desired polyphenylenes are facilely synthesized by Suzuki polycondensation,the uncoordinated palladium catalyst Pd(OAc)2 in situ covert into palladium nanoclusters.In the process of polymerization,emerging polyphenylene also serves as suitable support for nucleation and growth of the palladium nanoclusters.As a result,palladium nanoclusters are more stable against aggregation and maintain higher catalytic activity.Further structural characterizations reveal that the small-size palladium nanoclusters are uniformly dispersive.Pd@PHMP exhibits excellent catalytic performance when catalyzing hydrogenation of 4-nitrophenol(4-NPh)(reaction constant(k)=1.10 min-1).Remarkably,Pd@PHMP can reflect whole hydrogenation reaction process of various nitroaromatic compounds because light-emitting conjugated polymer PHMP shows different extent of fluorescence quenching when detecting nitro and amino.This work provides a mild,low-cost,and highly efficient method for synthesizing various polyphenylenes,which can be post-modified and encapsulated to make flexible fluorescent films.As short-wavelength emission fluorescence materials,these polyphenylenes can be used in industrial and commercial applications.At the same time,as long as the luminescent conjugated polymer are synthesized,small and uniformly dispersive palladium nanoclusters were simultaneously produced.The reduction process of different nitroaromatic compounds can be detected due to the remarkable combination of the fluorescence substrate and the active catalytic center-palladium nanoclusters.