Synthesis And Properties Of Fluorine-containing Polyhedral Oligomeric Silsesquioxanes(POSS) Modified Hyperbranched Polymer Light-emitting Materials For White OLEDs

As a new and efficient semiconductor planar light-source,white organic light emitting devices(WOLEDs)exhibit significant advantages in fields of flexible display and solid-state lighting.The unique three-dimensional structure of hyperbranched polymer(HBP)can inhibit the fluorescence quenching and crystallization of the polymers,which become a kind of luminescent material with great application prospects for WOLEDs.However,the efficiency,brightness and stability of the devices made of white light HBP need to be improved.To solve this problem,in this thesis,the HBP light-emitting materials were modified by introducing hydrophobic and highly transparent polyhedral oligomeric silsesquioxane(POSS)with hydrophobic groups(trifluoropropyl)into the side chains of the polymers.The polymer structure and properties were studied elaborately by changing the contents of POSS and the length of the linking group between POSS and the main chain in the polymers.The contents of the thesis were outlined as follows.Firstly,using 2,7-dibromo-9,9-bis(ethoxypropyl-hepta(3,3,3-trifluoropropyl)POSS)fluorene as the functional monomer,a series of white light HBP materials PFSDF10A2-POSSx was synthesized by Suzuki polycondensation.PFSDF10A2-POSSx maintained good photophysical properties and film morphology of white-light HBP materials.The hydrophobicity of the polymers is greatly improved due to the incorporation of trifluoropropyl on the peripheral groups of the POSS group.The water contact angle of the polymers was increased from 90°to 114.5°with increasing the content of POSS in HBP.The maximum brightness and current efficiency of the devices of polymer light emitting device(PLED)was improved,and the PLEDs showed good white light emission and high saturation with maximum color rendering index(CRI)of 96.In order to optimize the steric hindrance caused by the POSS group,the length of the alkyl chain between fluorene and POSS in the functional monomer was modified,and white-light HBP materials PFSDF10A5-POSSx and PFSDF10A7-POSSx were prepared by Suzuki polycondensation.The polymers also maintained good photoelectric properties and film morphologies.The degree of polymerization,the solubility,thermal stability and hydrophobicity of the polymers were greatly improved by increasing the alkyl chain length between fluorene and POSS.Therefore,the brightness and efficiency of PLEDs were significantly improved,and the maximum brightness was 424.1 cd/m~2,and the maximum current efficiency was 0.66 cd/A.The CRIs of PFSDF10A7-POSSx were around 90.Based on the results above,the white light HBP material PFSDF10A5-POSS20 based on nonyl linking group in the functional monomer and 20 mol%POSS in the polymer achieved the best performance with highest device efficiency.This work provided a new insight and experimental basis for the development of highly efficient and stable white light hyperbranched polymer materials.