Design And Synthesis Of Organic Optoelectronic Functional Materials Based On Spiro-Structure

Organic light-emitting diode(OLED)have attracted much attention in the field of organic optoelectronics due to their flexibility,low energy consumption,fast response speed,and self-luminescence.Given that the device performance and stability of OLED are directly affected by the emitters and host materials used in the light-emitting layer,organic optoelectronic materials have been widely studied by researchers.Among them,spiro compounds have become important building blocks for the construction of organic optoelectronic materials due to their special geometric configuration that can easily adjust the molecular structure and electronic properties.The spiro-structure is a stable threedimensional space structure composed of two carbocyclic skeletons sharing a spiro carbon through orthogonal connections,which is beneficial to suppress the π-π stacking of molecules in the solid-state.At the same time,the characteristics of multiple different substitution sites in the spiro-structure are beneficial to adjusting the molecular structure of the material and carrying out the precise modification.At present,many reports of thermally activated delayed fluorescence(TADF)materials and host materials based on spiro-structures have emerged.However,the spiro-structure still has many potentials worth exploring in the construction of organic optoelectronic materials.First,because the central carbon atom of the spiro-structure can break the conjugation,there are still few reports on the narrow bandgap material of the spiro-structure.At the same time,the current reports on spiro-based through space charge transfer(TSCT)materials mainly focus on the construction of luminescent materials and the modulation of donors,but there are few reports on the construction of host materials and the modulation of acceptors.In this paper,to explore more possibilities of the spiro structure in the construction of organic optoelectronic materials,we developed three types of spiro-based TADF materials based on the different characteristics of the spiro structure and conducted in-depth studies on their optoelectronic properties.In Chapter 2,we synthesized a strong donor N,N-diphenyl-9,9’-spirobi[fluorene]-2amine(SDPA)by linking 9,9’-spirobifluorene(SBF)unit and diphenylamine(DPA)unit,and then combined the donor SDPA and the acceptor acenaphtho[1,2-b]pyrazine-8,9dicarbonitrile(APDC)to construct a near-infrared(NIR)TADF emitter,3-(4-(9,9’-spiro Bis[fluoren]-3-yl(phenyl)amino)phenyl)acenaphtho[1,2-b]pyrazine-8,9-dicarbonitrile (SDPA-APDC).The frontier orbital distributions,photophysical properties,thermal properties,and electroluminescence properties of SDPA-APDC were systematically studied.The results show that SDPA-APDC has a narrow band-gap,small singlet-triplet energy gap(ΔEST),high photoluminescence quantum yield(PLQY),and favorable thermal stability.Consequently,SDPA-APDC based doped device and non-doped device achieved maximum external quantum efficiency(EQE)of 10.75%and 2.55%,respectively,and the corresponding emission peaks are 696 nm(red)and 782 nm(NIR),respectively.This work shows that the donor modulation by spiro-skeleton is an effective strategy to achieve efficient near-infrared emission.In Chapter 3,we constructed three donor-space-acceptor bipolar TADF host materials,OTBC,OPPC,and OCPC,by introducing electron-transporting benzophenone,hole-transporting 3,6-di-tert-butyl-9H-carbazole and 9-phenyl-9H-carbazole benzophenone at the C9 and C1 sites of the fluorene unit.The single-crystal structures,frontier orbital distributions,photophysical properties,thermal properties,and electroluminescence properties of the three emitters were systematically studied.The broken conjugated sp3 hybrid carbon spiro-atom makes the three emitters have high triplet energy levels,and the rigid and twisted backbone of the spiro-structures endow the three emitters with good thermal stability and small ΔEST.Consequently,the OTBC-,OPPC-,and OCPC-based phosphorescent OLEDs(PHOLEDs)with phosphorescent dopant FIrpic achieved maximum EQE of 13.2%,20.3%,and 21.3%,and the efficiency roll-off of 10.5%,15.0%and 3.4%at 1000 mA cm-2,respectively.The good device performance and stability provide a brand-new example for developing PhOLEDs.In Chapter 4,we constructed three donor-space-acceptor spiro-based through-space charge transfer(TSCT)emitters,SPS,SPO,and SPON,by introducing the same donor unit and different acceptor units at the C1 and C9 positions of the fluorene unit to explore the effect of acceptor modulation for the spiro-based TSCT emitters.The results show that the acceptor with too weak electron-withdrawing ability will cause the emitter to not have TADF properties,while the acceptor with too strong electro-withdrawing ability will increase the donor/acceptor(D/A)distance due to large steric hindrance,which will weaken the face-to-face π-π stacking interaction between D/A.Since SPO balances the electron-withdrawing strength and steric hindrance of the acceptor,the SPO-based device achieves the best electroluminescent performance(17.8%).This work shows that appropriate acceptor selection is essential for the development of efficient spiro-based scaffold TSCT emitters.