Design And Synthesis Of Novel Spiro-based Functional Materials In Organic Light-Emitting Diodes

Organic light-emitting diode(OLED)has attracted much attention since it could be used in solid-state lighting,large-area displaying,and wearable devices.Since the device performance is closely related to the applied materials,organic optoelectronic materials have been widely studied to improve the performance of OLED devices.Among them,spiro-structure is utilized to construct functional materials due to its special advantages.Firstly,in spiro-structure,two carbon rings connected through sp~3hybrid spiro carbon atom are perpendicular to each other,forming a stable three-dimensional structure and suppressing the?-?stacking effect in film state.Secondly,spiro-based materials have good diversity,which can be precisely modified by simply changing reactants.Moreover,spiro-based materials have good solubility,filming property and thermal stability.Nowadays,there have been lots of reports about constructing spiro-based thermally activated delayed fluorescence materials and bipolar hosts through introducing donor(D)and acceptor(A)respectively.But how to break the traditional methods and explore the potential of spiro-structure is still a worth-thinking problem.In this paper,we focus on two work.On one hand,spacial inter-molecular charge transfer were achieved in spiro materials by ingenious position engineering.Meanwhile,we also studied the direct influence of alkyl groups to materials'luminescence properties.On the other hand,a novel dispiro core was designed and synthesized,then the luminescence properties and devices performance based on dispiro materials were further studied.This work finds new possibilities of spiro-structure,providing a novel design strategy for further study.In Chapter 2,we constructed"D-space-A"type spiro-materials innovatively by introducing electron-drawing group to C1 site of fluorene.If we look closely to spiro-structure,the C1 site of fluorene is adjacent to the spiro center,and the spiro ring could potentially compel the C1 aromatic derivatives to exhibit characteristic coplanar configuration.Four blue emitters were synthesized and the design principle includes an annulated donor and a short D/A distance which together inhibit the acceptor from free rotation.In addition,the alkyl chain effect in modulating D/A interaction was also firstly observed in emissive compounds.Unusually,the 2-ethylhexyl branded-chain derivatives,however,have less steric hindrance effect and correspond shorter D/A distance which accounts for red-shift and higher photoluminescence quantum yields as compared to the n-hexyl analogues.All the materials show delayed fluorescence as well as spatially separated highest occupied molecular orbitals and lowest unoccupied molecular orbitals.In solution-processed devices,all materials exhibit outstanding performance and the maximum external quantum yields of devices are 14.16%for N2-6,17.60%for N2-8,14.71%for N3-6,18.87%for N3-8,respectively.This work provides an efficient strategy of regulating luminescence properties when designing materials.Besides the deeper investigation on spiro-structure,we also focus on the dispiro-structure.In Chapter 3,we first designed and synthesized the dispiro core,which extends in the longitudinal direction based on fluorene,anthracene and triphenylamine motifs.This dispiro core has great potential in modification and optimization as it can introduce functional groups on both ends.By incorporating electron-withdrawing groups on one end and electron-donating groups on the other end,two bifunctional materials with dispiro core have been designed and successfully synthesized through five steps reaction,including twice ring closing procedure.We explored the synthetic routes,configuration,photophysical,electrochemical,and thermal properties of them.Based on these properties,we attempted to fabricate red OLEDs with dispiro materials serving as hosts.And the maximum external quantum efficiency of 21.70%is achieved.This work is the first report of longitudinal extended dispiro core as the building block for host materials,and these results indicate that dispiro framework has a great potential to construct functional materials.