Design, Synthesis, And Characterization Of Light-Emitting Materials With Highly Morphological And Environmental Stability

Spectral stability of Ï€-conjugated polymer is of great importance for the application of electroluminescent materials, which is an overall result mainly associated with the thermal stability, morphological stability, electrochemical stability, and environmental stability etc. In this dissertation, we focus on the morphological stability and environmental stability. Three-dimensional and nonplanar building blocks, e.g., cross-shaped spiro, di-spiro, and complicated 9,9-diarylfluorene, have been designed to tune the intermolecular or interchain interaction of optoelectrical chromophores and Ï€-Ï€ stacking of conjugated backbones. On the other hand, the incorporation of antioxidant additives, e.g., hindered amine moieties, into typical optoelectronic system, especially polyfluorene, has also been explored to achieve stable blue light-emitting materials with long shelf and service life.First, we have developed efficient routes to synthesize thiophene-containing spiro compounds SDTF and SITF and constructed blue light-emitting materials, such as BBP-SDTF, BSBF-SDTF, T-SDTF, BSDTF -SDTF, BBP-SITF, and BSBF-SITF. T-SDTF bearing 6 thienyl rings exhibits very high luminescent quantum yield of 70% in dilute chloroform, which indicates that C-9 heteroaryl substituents via the spiro center have less effect on the light-emitting properties than via other manners, such as copolymerization. Cyclic voltammetry (CV) measurements demonstrates that the incorporation of electron-rich thienyl groups leads to an slight increase in the hole affinity and maintains wide bandgap at ca. 2.95 eV. In OLEDs fabricated by thermal deposition in a vacuum chamber, BSBF-SDTF exhibited no blue emission due to decomposition, which was monitored by MALDI-TOF-MS. It should be noted that blue light-emitting oligomers bearing thiophene moieties via spiro structure show unique regioselective feature at the C2 of thiophene due to the different reactivitybetween thiophene and benzene ring, which indicates that they will be useful for constructing complicated optoelectronic systems, such as host-guest system with energy transfer and rod-coil supramolecular system. In addition, solution casting devices can be fabricated by their derivatives tethered with soluble groups.Second, one strategy for devising new stable amorphous glassy materials are to incorporate the stiff three-dimensional nonplanar building blocks into the ordered architectures, in which the Ï€-Ï€ interaction of conjugated structure could be tuned by the isolation of nonplanar factors. In this chapter, the orthogonally cross-shaped di-spiro building blocks with unique geometric profiles have been explored to construct three-dimensional H-shaped architectures with blue light-emitting. The interior and exterior parts of the rigid H-shaped architectures exhibit different chemical circumstances identified by ¹³C-NMR. TDOF-DSFDITF possesses sufficient solubility due to the introduction of flexible alkyl side chains at the C-9 position of fluorene. TBP-DSFDITF shows a typical emission similar to terfluorene, which is an ideal model compound for study of the origin of low-energy green emission in polyfluorene.Third, a series of complicated 9,9-diarylfluorenes has been prepared by the BF₃Et₂O-mediated Friedel-Craft reaction, in which the electron-rich substituents, e.g., thiophene and oligothiophene, carbazole, poly(vinylcarbazole), triphenylamine, thienyl spiro compounds, phenyl ether, and pyrene etc. were efficiently introduced into the C9 position of fluorene. The 9,9-diarylfluorenes tethered with various functional substituents, e.g., bulky spiro units, hole-transporting moieties, and fluorescent dyes, will become promising building blocks for construction of optoelectrical materials. A big family of optoelectronic materials have also been designed and synthesized, including hole-transporting materials end-capped by 9-phenylfluoren-2-yl moieties, poly(vinylcarbazole) modified by 9-phenylfluoren-2-yl moieties and blue light-emitting terfluorene, stable solution-casting blue oligomers, and incorporation of pyrene into triphenylamine by 9-phenylfluoren-2-yl moieties. These complicated 9,9-diarylfluorenes and optoelectrical materials based on 9,9-diarylfluorenes show high thermal and morphological stability, in which the decomposition is up to 580℃. The OLED device with ITO/TPA(FP)₃/ ALQ₃/Mg:Ag configuration show high hole-transporting ability, in which the power efficiency is higher than that in similar NPB devices. The BF-BBPSITF-PF show high spectrum stability, in which the g-band at 530 nm did not appear under normal operation of thedevice.Fourth, the effect of a series of substituents in spiro structure, e.g., electron-rich arylamine moieties, electron-deficient fluoride and thiophene-S,S-dioxides, on the electronic structure has been estimated by preliminary quantum calculation, in which spiro-bridged thiophene-S,S-dioxides shown an excellent class of electron-transporting and hole-blocking materials. We proposed that Ï€-interrupted spiro framework is an effective tool to tune the intermolecular interaction of chromophore moieties, which has been confirmed by single crystal X-ray diffraction analyses. The model BSiSDTFO shows four types of supramolecular interaction, including C-H···O hydrogen bond, C-H···S hydrogen bond, C-H···π hydrogen bond, and Ï€-Ï€ stacking. In fact, BSiSDTFO is different from the non-spiro-bridged compounds in the literatures, in which the main drive forces to construct supramolecular network is the S···S and O···S short interaction contacts. It is noteworthy that the "dimmer" in BSiSDTFO did not represent the excimers because of the unique interrupting structure in the presence of spiro framework. BSiSDTFO shows high solid-state luminescent quantum efficiency (20%) and an increased electron affinity with LUMO energy of -3.24 eV, which reveal that BSiSDTFO is a potential electron-transporting and hole-blocking material.Fifth, to develop the methodology for the preparation of spiro compounds is important to expand the scope in different areas, e.g., molecular tectonics, enantioselective molecular recognition, molecular electronics, and optoelectrical devices. In this chapter, we successfully developed a one-pot method to prepare SFX. A plausible reaction pathway has been hypothesized. The experiments reveal that the SFX is a thermodynamic-controlled product and the FDPO is a kinetic-controlled product. We could draw another conclusion that FDPO could be efficiently consformed into SFX under Me₂SO₃H conditions. BSFXF based on SFX building block shows a stable blue light-emitting material.Sixth, degradation of organic and polymeric semiconductors is a key issue for commercialization. Therefore, it is very significant to improve the stability by incorporating antioxidant into the Tt-conjugated backbones. We firstly propose a stabilization strategy of general polymer for Ï€-conjugated semiconducting polymer. To suppress the g-band in polyfluorene, we designed an organic semiconducting antioxidant TMP-BPFT. We have also designed and synthesized a model terfluorene bearing hindered amine moieties to investigate the effect of stabilization onterfluorene. In addition, the polyfluorene end capped by the hindered amine moieties also has been synthesized. In the air-annealing experiments, it was found that the low-energy green emission was effectively suppressed, which is supportive to the induction that keto-defect was formed in exposure air under 200℃.In summary, we developed a one-pot method for the preparation of SFX and a BF₃ ·Et₂O-mediated Friedel-Craft reaction for the complicated 9,9-diarylfluorenes. The rigid nonplanar spiro and dispiro framework have been exploited to effectively tune the intermolecular interaction of functional moieties and the morphological stability has been improved. In addition, in order to overall improve the longevity of optoelectrical materials, we firstly designed organic semiconducting materials tethered with hindered amine moieties. Furthermore, we preconceive that a combination of morphological and environmental stability will be a perspective way to electroluminescent materials with high-performance and long service life.