Design,Synthesis,and Characterization Of Optoelectronic Materials Based On Spiro Structure

Spiro compounds are constructed by two orthogonal identical or different conjugated units through an sp3-hybridized carbon atom owing to the unique bonding angle,resulting in a rigid and orthogonal stereo configuration.Spiro-type materials can develop various efficient organic optoelectronic functional materials by effectively modulating the substituted position.Spiro-compounds,such as 9,9’-spiro-bifluorene(SBF)and 9-spiro-triphenylamine-fluorene(SAF),have been widely used in the organic light-emitting diodes(OLEDs)owing to their unique three-dimensional structure and good molecular rigidity,and a variety of efficient host and luminescent materials have been developed based on the spiro structure.How to further explore the potential of spiro structure has become a concern for the academic community.In this paper,the author first developed two novel host materials for high-efficiency red phosphorescence OLEDs(PhOLEDs)by introducing SBF groups at different substituted sites of naphthalene.Next,four light-emitting polymers based on the high-efficiency light-emitting small molecule DM-B,which had a spiro-structure as the skeleton,had been constructed.In order to integrate the light-emitting unit into the main chain of the polymers,fluorene and carbazole groups with different alkyl chains as the connecting unit had been copolymerized with DM-B derivatives.However,the triplet states of the polymer materials were reduced,leading to the disappearance of the TADF feature,resulting in poor device efficiency.Therefore,the strategy for constructing high-performance small molecules for spin-coated OLEDs by attaching alkyl chains away from the acceptor groups was developed.This paper provides a new design strategy for the development of organic optoelectronic materials and exploits the new avenue for the utilization of spiro materials.In Chapter 2,the simplest fused phenyl,naphthalene,was introduced into the pure hydrocarbon(PHC)host system for the first time,with SBF motifs at different attachment sites.In this way,1,4-SBF-Nap and 1,8-Oct-Nap were obtained with unique orthogonal configurations,rigid backbone,high glass transition temperatures,and high triplet energy levels,thus enhancing their abilities as host materials.It should be pointed out that there is an interesting cyclization reaction in 1,8-Oct-Nap,forming an octatomic ring structure instead of the SBF.Using bis(2-methyldibenzo[f,h]quinoxaline)(acetylacetonate)iridium(Ⅲ)(Ir(MDQ)2(acac))as the guest,red PhOLED devices based on these two hosts were fabricated,with maximum external quantum efficiencies(EQE)of 15.0%and 13.7%,respectively.This result demonstrates the diversity in the design of PHC host materials.In Chapter 3,light-emitting polymer materials,named 1Me-DMB-Cz,1Me-DMBFl,3Me-DMB-Cz,and 3Me-DMB-Fl,were obtained by copolymerizing the thermally activated delayed fluorescence(TADF)material,named DM-B,with the alkyl chainmodified fluorene and carbazole.Due to the introduction of connecting units,the triplet energy levels of these polymers were reduced,and their ΔESTS were significantly increased,which made it difficult for the polymers to maintain the original TADF properties and ultimately resulted in a decrease in device performance.Among the four light-emitting polymers,only the EQE of the device based on 3Me-DMB-Cz reached 11.6%,and the device efficiencies of other polymers were worse,which indicated that the method of directly introducing high-efficiency light-emitting small molecules into light-emitting polymers could not maintain the high device performances.Other effective construction methods should be explored to obtain high-efficiency spin-coated TADF materials based on high-efficiency evaporated TADF small molecules.In Chapter 4,based on Chapter 3,two spin-coated TADF luminescent materials were constructed,named C6-DMB and tBu-DMB.To improve the solubility,the tert-butyl group and the n-hexyl group as solubilizing groups(SGs)were introduced,respectively,into the C7 site of the fluorenyl group in DM-B.The C7 site of the fluorenyl group exhibited the least influence on the donor/acceptor and could maintain the TADF properties.Utilizing them as light-emitting materials in spin-coated OLEDs,high-efficiency devices with maximum EQEs of 21.0%and 21.7%,respectively,were obtained.This work provides a new strategy to construct highly efficient spin-coated TADF materials by introducing SGs on the "bridge" groups of highly efficient evaporating luminescent materials to increase their solubilities,suitable for spin-coated devices.