Study On The Spectral Characterization Of Conjugated Polymer Aggregates And The Effect Of The Photoelectric Properties

Since the conjugated polymer has good film forming property,a luminescent film can be prepared by a solution processing method to simplify the production process.Conjugated polymer is a great potential luminescent material.For conjugated polymers,increasing efficiency and stability and extending life are the problems they face.The aggregation structure of the conjugated polymer in the solution can directly affect the aggregation structure of the film,thereby affecting the photoelectric performance of the device.UV-vis,PL and transient absorption spectrum can characterize the aggregation structure properties of the conjugated polymer.In this paper,the aggregation structure of conjugated polymers was characterized by various spectra,and the effects of chiral side groups,solvent on the aggregation structure of conjugated polymers and their effects on photoelectric properties were discussed.一、Effect of racemic side groups on entanglement of conjugated polymer chains.Clear structure characterization is the basic of performance analysis,which is difficult for the complex structure of amorphous conjugated polymer.In this work,we have given solid evidence in copolymer of fluorene and carbazole that the carbazole with racemic branched alkyl side chain tend to form chain entanglement in high concentration of solution and thin film.The single crystal structure of two racemic carbazole dimer with stronger π-π interaction,which 1HNMR peaks is well corresponding to that of racemic polymer at high concentration and proves the existence of chain entanglement in racemic polymer.The chain entanglement segment with high molecular weight and low energy level(estimated as about 3%and absent in the chiral polymer)have enriched at the interface during film fabrication,which induce strong charge trapping and excited state quenching during the working of optoelectronic devices.These chain entanglement would be well restrained by chiral substitution,which induce one order of magnitudes improvement of device brightness and efficiency.These results indicate that the chain entangle at interface and charge trapping play the key role of bad device performance,which help to explore the instability origin and performance promotion.二、Solvent-induced reversible physical gel improves the stability of conjugated polymer devices.We found P-PPV formed a thermoreversible gel at a certain concentration when the R-limonene as solvent,and.The AFM of the spin-coated film shows that the P-PPV has a chain untangling under the action of R-limonene in the dilute solution,and the separated chain prevents the fluorescence quenching caused by the non-radiative transition,which can improve fluorescence quantum yield(PLQY)and fluorescence lifetime.Under concentrated solution,the gel temperature of P-PPV is in the temperature range of 55-35℃.During this temperature range,the isolated molecular chain begin to attract each other and the molecular chain have π-π stacking results in physical cross-linking and gelation.P-PPV is more stable due to less entanglement between molecules and the appearance of gel points,which has the effect of enhancing fluorescence emission.Cross-linking between chains makes P-PPV more stable,improving device stability,brightness and lifetime.三、Effect of chiral side groups on aggregate structure of PPV derivatives.We attempted to investigate the effect of racemic and chiral side groups on the entanglement of PPV derivatives(MMB-PPV and R-MMB-PPV).The UV-vis,PL,PLQY,fluorescence lifetime,Raman,FT-IR tests show that there is no effect on the entanglement of the R-MMB-PPV.This may be due to the fact that in R-MMB-PPV,the alkyl chain length is relatively short,the solubility is poor,and the chain entanglement is strong.However,the choice of stable chiral monomers is limited under current experimental conditions.In summary,the phenomenon of chain entanglement in the derivatives of polyfluorene,polycarbazole and PPV has a significant effect on the photoelectric properties.The chiral side chain and the interaction between the solvent and the main chain,etc.,have important significance in the regulation of aggregate structure and photoelectric properties.