Synthesis And Photophysical Properties Of Five-membered Azahetero Fused Ring π-conjugated Molecules

Organic conjugated molecules have attracted considerable attention in recentyears due to their potential applications in different fields, such as light-emittingdiodes, photovoltaic cells, optical power limiting, organic field-effect transistors, andso on. Besides small organic molecules and polymers, a new class of linear-shaped,star-shaped and dendritic oligomers has also attracted great attention at present. Theseoligomers have definit molecular structure and higher purity. It is well-known that theazoheterocyclic compounds, such as carbazole, pyrazine and benzothiadiazolederivatives possess excellent optical and electrochemical properities. Therefore, theyalways could be acted as building blocks of fuctional materials for OLED or solarcells. Especially, the introduction of azoheterocyclic compound can increase the holeor electron mobility of the materials, and improve thermal and electrochemicalstability. In this thesis, we mainly focus the synthesis of5-membered azohetero fusedring compounds and the investigations of their photophysical and electrochemicalproperties. Some creative results have been obtained, and outlined below:(1) Two new D-A-D type phosphorus (V) porphyrin derivatives1and2functionalized with axial carbazolylvinylnaphthalimide units were synthesized. Theabsorption bands of the obtained phosphorus (V) porphyrins were in the range of250-640nm with high molar absorption coefficients, meaning strong light-harvestingabilities. Notably, it was found that the devices [ITO/PEDOT:PSS/organic activefilm/LiF/Al] based on1and2gave obvious incident-photon-to-current conversionefficiency (IPCE) response. The IPCE response of the device based on compound1isrelative low, and the highest IPCE value (0.20%) exhibited at Soret band of1.However, the device of2gave higher IPCE value (2.76%) at the wavelength of Soretband of2. Notably, the IPCE response of the devices suggests the electron transferfrom the axial units to the phosphorus (V) porphyrin cores. Therefore, thesephosphorus (V) porphyrin derivatives might be good candidates for photovoltaicmaterials due to their broad absorption in the visible region. (2) Through Suzuki cross-coupling reaction of the brominated oligocarbazolesand9,10-bis(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)anthracene, well-definedmonodisperse oligocarbazoles-functionalized anthracenes An-OCZn (n=1,2,3)have been synthesized. They showed good solubility in common organic solvents,including dichloromethane, chloroform, toluene, ethyl acetate, and tetrahydrofuran. Itshould be noted that, introducing of oligocarbazoles in9,10-position of anthracenesuppressed the formation of the excimer of anthracene cores. Therefore, An-OCZnhad high fluorescence quantum yields (>66%). In addition, An-OCZn exhibitedgood electrochemical and thermal stabilities. Thus, theseoligocarbazoles-functionalized anthracenes would be a class of promising candidatesfor novel blue-emitting materials employed in OLEDs or related devices.(3) A series of pyrene derivatives TP, TCP and TCCP have been successfullyprepared via alternately Heck and Wittig reactions. The formation of the excimer ofpyrene units could be completely suppressed, so they afforded high fluorescencequantum yields (>52%). TP, TCP and TCCP possessed excellent thermal stabilitywith initial decomposition temperatures over369C. Notably, non-doped organiclight-emitting diodes based on these compounds as emitters as well ashole-transporting layer were fabricated, which gave strong green light. Especially, thedevice based on TP achieved a good performance with a low turn-on voltage of2.80V, a maximum luminance29980cd/m2, a power efficiency of2.67lm/W, a currentefficiencies of3.34cd/A. Therefore, these pyrene derivatives can be used aspromising green light materials for efficient non-doped OLEDs.(4) Three π-conjugated dendrimers (G1-TBT, G2-TBT and G3-TBT) bearing atriphenylamine moiety as dendrons and benzothiadiazole (BT) as core have beensynthesized through a convergent synthetic strategy. It was found that threedendrimers could emit strong red fluorescence with high fluorescence quantum yields(>40%). Increasing the generation number of dendrimers induced the red-shift of theabsorption and emission bands in solutions. The maximum absorption and emissionpeaks in film were significantly red-shifted compared with those in solutions, whichwas due to the aggregation effect in films. In addition, the fluorescence spectrasuggested the existence of light-induced energy transfer from peripheral dendrons tobenzothiadiazole cores. The electrochemical measurements implied that the frontierorbital (HOMO and LUMO) energy levels had a slightly relationship with the generation number of dendrons. So, these dendrimers may act as light emittingmaterials for the OLED.