Cyano-substituted Water/alcohol Soluble Conjugated Polymers:Synthesis And Application In Photocatalytic Hydrogen Evolution

Photocatalytic water splitting?including hydrogen evolution and oxygen evolution?has received wide attention in the past decade since it provides a clean and sustainable way to transfer solar energy into fuel.Organic semiconductors are regarded as promising photocatalytic materials for hydrogen evolution due to their clear structure and adjustable photoelectrochemical properties.Among them,water/achohol soluble conjugated polymers exhibite huge potential for the use of photocatalytic hydrogen evolution due to their good dispersition in water.However,most polymeric photocatalysts suffer from unexceptional hydrogen evolution rate due to the challenge in molecular design and understanding of highly efficient organic photocatalyst.In this dissertation,a series of novel water/alcohol soluble conjugated polymers were developed in order to explore the effects of chemical structures on the opto-electronic properties and photocatalytic performance for hydrogen evolution.In Chapter 2,three quaternizated conjugated polyelectrolytes?PFBr-Ph,PFBr-Ph F and PFBr-Ph CN?with different substituents?-F and-CN?were designed and synthesized.Compared to the unmodified polymer,the-F and-CN modified polymers showed 2.9-and 12-times improvements in the hydrogen evolution rate(3?mol h^-1 vs 8.8?mol h^-1 vs 38.3?mol h^-1).Notably,-CN substituents in the polymer could reduce the exciton binding energy,induce closer packing and higher crystallinity,improve the charge transporting,and reduce the charge recombination.Moreover,higher efficient exciton generation and charge transfer efficiency to cocatalysts were observed in-CN modified polymers,indicating the great promise of using substituent regulation to achieve high-performance organic photocatalysts.In Chapter 3,we synthesized a novel dicyano-substituted conjugated building block BTCN and copolymerized it with oligoethylene glycol?OEG?funtinalized bithiophene unit,resulting in a series of novel D-A-type conjugated polymer PTh-BTCNx.The increasing of the copolymerization ratio of BTCN results in enhanced intramolecular charge transfer and broadened absorption spectrum of the polymers.However,the electron withdrawing capability of the BTCN is too strong,leading to the much lowered energy level in polymers,which is not conducive to the photocatalytic hydrogen evolution reaction.The hydrogen evolution rate of PTh-BTCN10 with 10%BTCN is only 114?mol g^-1 h^-1.In Chapter 4,we synthesized a polythiophene based water/alcohol conjugated polymer PTh0,and further incorporated 30%1,4-dicyanobenzene?Ph CN?unit into its backbone,resulting in a novel D-A water-alcohol conjugated polymer PTh-Ph CN30.Compared to PTh-BTCNx in the previous chapter,PTh0 and PTh-Ph CN30 possess appropriate energy levels,and therefore sussessfully enable efficient photocatalytic hydrogen evolution.It was found that PTh-Ph CN30 exhibits stronger?-?stacking and better charge transport characteristics than PTh0.The photocatalytic hydrogen evolution efficiency of PTh-Ph CN30 reaches 4 mmol g^-1 h^-1,which is 7.9 times than that of PTh0.Furthermore,surfactant F127 was used to improve the water dispersibility of the polymer,which enables the hydrogen evolution efficiency of 12mmol g^-1 h^-1 for PTh-Ph CN30.