Synthesis And Properties Of Organic Light-emitting Materials Based On Enaminones And Their Boron Complexes

Enaminones and their boron complexes have facile synthesis and structural versatility,tunable photophysical properties and excellent stability.The formation of four-coordinate organoboron compounds can efficiently enhance their molecular rigidities and electron-withdrawing abilities,which are ideal to construct purely organic thermally activated delayed fluorescence(TADF)materials as acceptor units.However,there are only limited examples of light-emitting enaminones and their boron complexes reported,which always exhibit feeble solid-state emission.Especially,their application as TADF acceptors lags far behind three-coordinate organoboron compounds.In this thesis,we designed and synthesized novel enaminones and their boron complexes-based organic optoelectronic materials with remarkable luminescent properties in solid states through tuning their molecular structures and intermolecular interactions,and explored their ability to construct red TADF materials as acceptor units.The main contents are follows:1.Trans-enaminone and cis-enaminone fluorescent molecules were synthesized according to mild and effective aza-Michael addition reaction,and their luminescence properties were regulated by introducing bromine atomic substituents.Three trans-enaminone fluorescent molecules with different number of bromine atomic substituents,TE,BrTE and Br3TE have shown aggregation induced luminescence(AIE)behavior.For BrTE containing one bromine atom,two types of crystals with different fluorescence properties are obtained:BrTE-B and BrTE-G.The crystal BrTE-G containing halogen bond interactions has a higher fluorescence quantum yield(9.6%)than that of BrTE-B without halogen bonds(1.4%)and nonbrominated TE(2.1%).The crystal of Br3TE with three bromine substituents exhibits an even higher fluorescence quantum yield(12.5%)than BrTE-G.Two cis-enaminone molecules BrE and HE with intramolecular hydrogen bond formed highly planar conformations are AIE-active which are different from typical AIE molecules showing twisted or helical molecular structures.The fluorescence quantum efficiency of bromine-substituted BrE crystal is 18.1%,ten times as large as that of unsubstituted HE crystal due to form intermolecular Br…Br halogen bonding to block nonradiative relaxation pathways efficiently but also promote the radiative process.2.A series of enaminone boron complexes were synthesized by complexing cis-enaminone ligands with boron compounds,and the effects of substituents on luminescence behavior were studied.Through changing the complexing group on boron(fluorine,phenyl,pentafluorophenyl),three boron complexes BF,BPH,BPF5,were obtained based on HE ligand.All three boron complexes have higher crystal luminescence efficiency(32.3%,13.6%and 35.6%)than HE(1.8%),especially BF and BPF with fluoride and pentafluorophenyl substituted show higher solid-state luminescence efficiency than BPH with phenyl substituted due to their higher rigidity of enaminone boron chelated six-membered ring,accompanied by multiple intermolecular C-H…F hydrogen bonds.Different electronic pushing and drawing substituents(dimethylaminobenzene,methoxy,cyanide and nitro)were connected to the B-O and B-N sides of BF,respectively,which could regulate the photophysical behavior effectively.Among them,NMe2-BF with dimethylamine on the B-O side was conducive to the formation of quinone structure,and green fluorescence emission with narrow full width at half maximum(FWHM)was observed in the single molecule states(solution state:PLQY is 89.3%,FWHM is 50 nm;doped film:PLQY is 98.6%,FWHM is 55 nm).However,due to ?-? stacking,the crystal luminescence efficiency decreased to 21%and FWHM increased to 92nm.When dimethylamine was introduced on the B-N side,the emission peak of BF-NMe2 was red shifted more than 80 nm red than that of NMe2-BF.The emission peak of BF-NMe2 crystal reached to 640 nm,presenting pure red emission.3.A series of solution-processed twisted donor-receptor(D-A)structured orange-red and red TADF molecules were designed and synthesized with 9,9-dimethylacridine(DMAC)as the donor and enaminone boron complexes as the receptor.Two TADF molecules,DMAC-BF and BF-DMAC,were prepared by changing the link position of the donor unit on the enaminone boron complexes.Due to stronger molecular rigidity,the PLQY of the DMAC-BF with donor attached at the B-O side is higher than BF-DMAC with donor set on B-N side.The fluorescence quantum yield of DMAC-BF is 52%,while BF-DMAC is only 29%.The device based on DMAC-BF achieved the maximum external quantum efficiency(EQE)of 1 1.3%,and displayed orange-red emissions with the peak at 598 nm.Two red TADF molecules,DMAC-BPF5 and DMAC-BPF 5-CN,were synthesized with pentafluorobenzene as complexing group and further introducing cyanogen into the structure of enaminone boron complexes.Compared with DMAC-BF,The ?ESTS of DMAC-BPF5 and DMAC-BPF5-CN reduced from 0.09eV to 0.22 and 0.07 eV,and delay fluorescence life reduced from 164 ?s to 1.75 and 0.98 ?s.The OLEDs based on DMAC-BPF5 and DMAC-BPF5-CN realize red electroluminescent with at 620 nm and 643 nm,and the maximum EQE reached 12.5%and 6.8%respectively.