Silicon-containing Conjugated Organic Optoelectronic Materials: Design, Synthesis, And Property Investigations

The organoelectronics including organic light emitting diodes(OLEDs), organic photovoltaic cells(OPVs), organic field effect transistors(OFETs) have been a flourish of developments over the past few decades. Recently, silicon incorporated organic optoelectronic materials have received tremendous attentions in developing new organic semiconductors. The electronic structures and properties of organic semiconductors could be effectively tuned through silicon incorporated, which is attributed to the the particular orbital interactions between the d-oribital in the outermost layer of Si(σ*–π* conjugation) and the π-conjugated framework. On the other hand, silicon serve as an inorganic functional material, can be widely applied in modern electronic appliances and other industries. In addition, as a kind of organic-inorganic hybrid materials, silicon-based organic optoelectronic materials have great potentials in scientific research and commercial development. For these reasons, this thesis concentrated on design, synthesis and device properties of optoelectronic materials through silicon incorporation. Firstly, in order to solve inherent conflict between the high triplet energy level and charge transportation performance of host materials, we designed and synthesized a series of host materials containing aromatic silane and carbazole with both high triplet energy level and excellent charge transportation performance, and their electrophosphorescent devices performance had been studied. Secondly, aiming at solving the synthesis difficulty of introducing silicon into large π-conjugated framework, we extended the transition metal catalyzed Si-H/C-H coupling to nitrogen-containing substrates, offering a new route for the highly efficient synthesis of phenazasilines and also fabricated preliminary blue PhOLED device based on phenazasilines as the host material. Thirdly, in order to synthesis of heteroatom incorporated π-stack polymer, we introduced the silicon into the polyvinylcarbazoles to replace the nitrogen atoms to develope a new type of π stack polymer-polyvinylsilafluorene, and investigated the performance of nanofuse device with the polymer-polyvinylsilafluorene as an active layer. The details are as followed:1) Four host molecules with aromatic silane/carbazole binary system were synthesized by directly connecting the tetraphenyl silane with carbazole group through the insulative σ bond(Si-N bond). The single crystal structure of these compounds had been analyzed as well. The fundamental properties of the compounds were investigated by thermal analysis, spectroscopy, electrochemistry and other testing methods, and a detailed relationship between structure and properties of the compounds was studied by quantum chemistry calculations. Through all these works, we explored the application of these materials in blue electroluminescent phosphorescent devices as the host material. The experimental and theoretical results showed that these new materials have excellent thermal stability(Td: 295-359oC, Tm: 206-268oC), high triplet energy level(3.0 eV), suitable HOMO(-5.65~-5.83 eV) and excellent film-forming property. The blue electroluminescent device based on these host materials obtained a preferable performance with low turn-on voltage of 3.0 V, 23.4 cd/A, 19.3 lm/W and 12.4% for the maximum current efficiency, power efficiency and external quantum efficiency, respectively.2)A series of host materials containing Si-N and Si-C bonds have been designed and synthesized through multiple insulative connections. Fondamental properties have been systematically characterized by thermal analysis, spectroscopy, electrochemistry and other testing methods and PHOLEDs were also explored. Our research demonstrated that improved thermal stability(Td: 295-427oC, Tm: 206-272oC), similar photophysical properties(both in absorbtion and emission spectra), high triplet energy level(~3.0 eV) and suitable HOMO(-5.65~-5.90 eV) and LUMO(-1.95~-2.23 eV) levels have been achieved through introducing triphenylsilane which is a weak electron-withdrowing unit by insulative Si-C bond. Blue PHOLED device indicated that the system has extremely low operating voltage(2.6 V) and good device performance(CE: 14.8 cd/A).3)Two ternary host materials were designed and synthesized based on arylsilane-benzenecarbazole. We proposed a design strategy to build the ideal host material for blue PhOLEDs via limiting triplet exciton formation by controlling exciton formation cross section and triplet exciton formation fraction of the host materials. A detailed study of the photophysical and electrochemical properties of these host materials were carried out by combination of theoretical and experimental methods. The results showed that SiPTCz and SiPCz have similar photophysical and electrochemical properties, but the biggest difference is that Si PCz has smaller triplet exciton formation formation cross section and triplet exciton formation rate. The limitted triplet exciton formation rate of host materials can well suppress the quenching effects of TTA and TPQ caused by the triplet excitons of host materials. Based on such a host molecule of SiPCz, highly efficient and stable blue PhOLEDs were fabricated and showed maximum efficiencies of 43.7 cd/A for CE, 32.7 lm/W for PE, and 20.7% for EQE.4) Two π-extended phenazasilines were designed and synthesized, which extend the rhodium-catalyzed Si-H/C-H coupling to nitrogen-containing substrates, offering a new route for the highly efficient synthesis of phenazasilines, especially of the π-extended phenazasilines. This method has some advantages such as high yield, easy to get the precursor and operate, and can be extended to synthesis of other types of phenazasilines derivatives. A detailed study of the photophysical and electrochemical properties of these compounds were carried out by combining experimental and theoretical calculation. The results showed that the obtained phenazasilines exhibit good thermal stability(Td: 246oC, Tm: 150oC), high triplet energy level(~3.0 e V), appropriate HOMO and LUMO levels. For the first time, the preliminary blue PhOLED device based on phenazasilines as host material was fabricated; the high device performance with high CE(24.2 cd/A), PE(20.3 lm/W) and EQE(11.2%) highlights the great potential of the optoelectronically active phenazasilines in organic electronics.5) By introducing the silicon atoms into the polyvinylcarbazoles to replace the nitrogen atoms, silicon incorporated π stacking one-dimensional polymer—polyvinyl methyl silicone fluorine(PVMSi F) were designed and synthesized. The newly prepared silicon-containing π-stacked polymer of PVMSi F exhibits extraordinary molecular nanofuse as well as excellent WORM memory behaviors. A detailed study of the molecular mechanism of resistance wire device was carried out by combinational analysis of UV-Vis and PL spectra, micro-PL, XRD and joint theoretical investigations of DFT and MD simulations. The conductivity switching mechanism of the polymeric nanofilm, understood in a silicon-stimulated filament theory, was proposed to be related to the π-π stacking conductive filaments formation and deformation control upon electron/hole injection. The building of optoelectronic functional materials of homopolymer of vinyl silafluorene by silicon incorporation has provided a viable research approach for design π-π stacked polymer with high performance.