Synthesis And Properties Of Thermally Activated Delayed Fluorescent Materials Based On Oxidized Thioxanthone

Thermally activated delayed fluorescence(TADF)materials have been regarded as the third generation emitters for organic light-emitting diodes(OLEDs),making up for the shortcomings of the traditional materials.In contrast,organic fluorescence emitters with thermally activated delayed fluorescence(TADF)can reach a high internal maximum quantum(100%).The TADF molecules contain a process of thermally activated up-conversion from T1 to S1 state without using rare metals.In recent years,there are mianly three research interests reported in the literatures:i)the exploration of TADF luminescence mechanism,ii)the molecular structure designing stretegy of TADF small molecules,exciplexes,and polymers,and the application of TADF emitters as an illuminating layer in organic light-emitting diodes(OLEDs).In this thesis,two small molecules with oxidized thioxanthone(TXO)as the acceptor moiety,phenothiazine(PTZ)and carbazole(CZ)as the donor moieties,respectively,were designed and synthesized(TXO-PTZ and TXO-CZ).According to the DFT calculation results,the HOMOs of TXO-PTZ and TXO-CZ were mainly dispersed over the PTZ and CZ moiety,while their LUMOs were localized on TXO moiety,showing a distinct D-A distribution.The doped OLEDs of TXO-PTZ and TXO-CZ using SimCP3-Ph as host materials,have achieved maximum current efficiency of 9.10 cd/A and 46.6 cd/A,maximum power efficiency of 3.5 lm/W and 19.4 lm/W,and maximum external quantum efficiency of 3.00%and 14.5%,respectively.Then TXO-PTZ and 9-(4-(bis(4-bromophenyl)(methyl)silyl)phenyl)-9H-carbazole were polymerized to polymers with the ratios of 12:88 for P1 and 18:82 for P2.The introduction of the triphenylmethylsilazazole unit into mianchains can effectively suppress the exciton quenching.Compared with the small molecules,the thermal properties of the P1 and P2 are significantly improved.Polymers can better achieve an effective reverse intersystem crossing from T1 to S1.The TADF-OLEDs based on P1 showe a maximum current efficiency of 16.70 cd/A and a maximum power efficiency of 10.50 lm/W and an external quantum efficiency of 5.38%,which is superior to the performance of TADF-OLED devices based on TXO-PTZ.P1 was processed into two kinds of oriented fibers with different diameters.The fibers with smaller diameter exhibit better TADF characteristics,and moreover the charge transfer mechanism,radiative decay rate coefficients and photolumiance process are all closely related with the oriented structure of TADF polymer emitters.