Studies On The Construction Of Stretchable Conjugated Polymers Through Siloxane Side Chain Engineering

Stretchable semiconducting polymers have received considerable attention in recent years,due to their molecular designability,solution processability,and the ability to prepare large-area flexible or elastic electronic devices.A great deal of work has been performed to develop high-performance stretchable semiconducting materials,focusing on the main and side chains of conjugated polymers.Side chain engineering can be used to modulate the solubility and mobility of semiconducting polymers,as well as their stretchability and ductility.Although some progress has been made in side chain engineering,most stretchable semiconducting polymers exhibit low charge mobility and show varying degrees of degradation in charge transport properties after stretching.Therefore,the simultaneous improvement of charge mobility and tensile ductility of semiconducting polymers through effective side chain engineering,has become a key issue in this field of research.In this thesis,the effect of hybrid siloxane-based side chains on the aggregate-state structure,solubility,electrical properties,and mechanical properties of conjugated polymers was investigated,with the aim of obtaining high-performance and multi-functional conjugated polymers,based on the design and synthesis of semiconductor materials.The main results have been achieved as follows:1)Novel hybrid siloxane side chains were designed and synthesized,which were able to significantly improve the solubility of the semiconducting polymer.The introduction of fluorine atoms into the polymer backbone effectively enhances the crystallinity of the films,leading to improved device performance.With the synergistic effect of main and side chain structure,a semiconducting polymer（PAIIDBFT-Si）with high solubility and mobility was successfully prepared.Thin-film transistors prepared using tetrahydrofuran,ether,and alkane solvents achieved hole mobilities of 3.78,2.14,and 2.34 cm²V^-1s^-1,respectively.2)The effect of carbon chain length in the hybrid siloxane side chains on the aggregation and properties of semiconducting polymers has been systematically investigated.Three semiconducting polymers（PIID-C₅-Si₇,PIID-C₆-Si₇,PIID-C₇-Si₇）were prepared by changing the carbon chain length in the long linear hybrid siloxane side chains.As the carbon chain length increased,the polymer films showed enhanced crystallinity,increased stacking order,and improved charge transport properties.The processing solvent was also found to significantly affect the pre-aggregation of the polymer in solution and the ordering of the molecular stacking in films.Based on the high solubility of the polymer,flexible transistor arrays were prepared,with stable electrical properties under different bending conditions.3)The effect of silicon chain length in the hybrid siloxane side chains on the aggregation and properties of semiconducting polymers has been further investigated.Five semiconducting polymers（PTDPPSe-x Si,x=3～7）were prepared by precisely controlling the silicon chain length in the hybrid siloxane side chains.As the silicon chain length increased,the solubility increases,solution pre-aggregation weakens,film crystallinity decreases,and molecular stacking changes.The charge transport properties of semiconducting polymers can be effectively tuned by controlling the silicon chain length.Increasing the silicon chain length leads to a decrease in the elastic modulus and an increase in the fracture strain of the semiconducting polymer.Stretch-induced enhancement of charge transport properties was found in the prepared donor-acceptor conjugated polymer,and the hole mobility was higher than 1 cm²V^-1s^-1 at 100%strain.4)The feasibility of side chain engineering in the preparation of high-performance stretchable n-type semiconductors was explored.High performance stretchable n-type semiconducting polymer was prepared by selecting electron transporting BDOPV as the conjugated main chain,while changing the side chain type and increasing the side chain density.It was found that the side chain engineering enables the surface morphology,molecular stacking,and charge transport properties of the polymer to be regulated.Moreover,side chain engineering can reduce the crystallinity and elastic modulus of the polymer,thereby improving the ductility.CSi-PBIBDF achieved an electron mobility of 0.21 cm²V^-1s^-1at 100%strain,which is higher than that of its unstretched films.The use of both alkyl side chains and hybrid siloxane-based side chains has been shown to be an effective strategy for the construction of stretchable n-type semiconducting polymers.