Design And Characterization Of Novel Carbazole-Based π System

In the information society, opto-electronic materials are essential to our daily life. Electronic devices are getting smaller everyday. Compared with inorganic materials, organic opto-electronic materials such as organic semiconductors applied in organic light emitting diode (OLED) and organic field effect transistors (OFET) are more promising in fabrication of thin film devices, also more affordable. Carbazole is known as heterocycle for a long time and has wide applications in dyes, medicine, electronic etc. Carbazole derivative is one of the most important species in OLED and OFET materials for its electron-rich property and rich chemistry. In this thesis, new carbazole derivatives and other types of organic opto-electronic materials are synthesized and their applications in OLED, OFET devices and fluorescence chemosensors are explored.Chapter 1 introduced the current progress in organic opto-electronic materials and the structure of OLED and OFET devices. Carbazole based semiconductors and their applications in OLED and OFET were reviewed according to their structures. And the research projects in this thesis were outlined.In Chapter 2. a series of new carbazole-based luminophores (Ⅱ-1-Ⅱ-12) were synthesized. well characterized and exhibited aggregation-induced emission enhancement (AIEE) properties. The obtained experimental results demonstrated that the attachment of aromatic rotors to luminophore moieties would lead to the decreased quantum yields measured in diluted solutions, the more rotors attached, the less quantum yields tested, further confirming that the AIEE phenomena were caused by the restrictions of the intramolecular indolyl vibrational and rotational motions, in an indirect manner.In Chapter 3, novel carbazole and thiophene fused heteroarene derivatives III-5a andⅢ-5b were conveniently synthesized from a new reactive intermediate, 2,3,6,7-tetrabromocarbazole, using Suzuki reaction followed by FeCl3 oxidative cyclization. The solubility ofⅢ-5a andⅢ-5b was turned by the alkyl chain at the a position of thiophene groups. 1H NMR results, fluorescence and absorption spectra indicated their tendency to self assemble in condensed solutions and in thin films. Hole mobility of 1.5×10-2 and 2.6×10-2 cm2V-1s-1 were achieved from vacuum sublimed and solution processed devices respectively. Devices fabricated on OTS treated substrates showed better performance than devices fabricated on bare substrates. Using the synthetic method of Chapter 3, replacing thiophene with benzene, a series triphenylene (TP) containing and carbazole cored heteroarene derivatives were synthesized in Chapter 4. Since benzene is less reactive than thiophene in the presence of FeCl3, by adjusting the reaction condition,1 TP containing semi-cyclized compoundsⅣ-2 and 2 TP containing full-cyclized compoundsⅣ-3 were obtained.Ⅳ-2 andⅣ-3 were characterized and their OFET devices were fabricated. Devices usingⅣ-3 as active layer showed better film morphology and performance thanⅣ-2. Hole mobility of 1.0-2.3×10-3 cm2V-1s-1 were achieved from vacuum sublimed devices using OTS treated substrate.In Chapter 5, two star-shaped molecules V-5 and V-6 were synthesized using carbazole as core with thiophene or bithiophene substituted on its 1,3,6,8 positions. OFET devices were fabricated using V-5 and V-6 as active layer. Hole mobility of 5.2×10-5 cm2V-1s-1 was obtained by device of V-6. And device of V-5 showed no field effect. The poor performance of V-5 and V-6 should be ascribed to the large steric hindrance of substitution on 1 and 8 position of carbazole, which might hinder the packing of molecules.In Chapter 6, a series carbazole core dendrimersⅣ-7～VI-14 were synthesized with different fluorescent groups substituted on 1,3,6,8 position of carbazole.Ⅳ-7～Ⅳ-14 showed excellent solubility and their solid thin films can be easily fabricated by spin-coating. The thin film fluorescence spectra ofⅣ-11-Ⅳ-14 were identical with their solution fluorescence spectra with even smaller full width at half maxima (fwhm), the CIE coordinates of which were located in deep blue region.Ⅳ-11-Ⅳ-14 showed great potential in application of solution fabricated deep blue OLED devices.In Chapter 7, three conjugated dendrimers VII-4-VII-6 containing tetraphenyl-benzene, triphenylamine and fluorene groups were synthesized. They all have excellent solubility in common organic solvent and their OLED devices were fabricated by spin-coating. The electroluminescent (EL) spectra of VII-4-VII-6 were slightly hypsochromic shifted with smaller fwhm down to 44 nm, compared with their fluorescent spectra in solution and thin films. And the CIE coordinates of their EL spectra were all in the deep blue regions. All the devices can be turned on below 4 V. A maximum brightness of 2299 cd/m2 was achieved by the devices ofⅦ-6. The device ofⅦ-4 showed a current efficiency up to 0.90 cd/A at 100 mA/cm2. In Chapter 8, a new D-A-D type AIE material VIII-1 were synthesized using tetraphenylethylene (TPE) and bisphenylfumaronitrile as building block. Crystalline VIII-1 was a yellow powder with yellow fluorescence, while amorphousⅧ-1 was an orange powder with orange fluorescence. These two different states ofⅧ-1 were characterized. The fluorescent spectra and UV-Vis absorption spectra ofⅧ-1 were solvatochromic to the change of solvent polarity. AndⅧ-1 showed typical AIE behavior in the solution of THF/H2O and DMF/H2O. White light OLED were fabricated usingⅧ-1 as orange light emission layer. And the maximum brightness of 1708 cd/m2 and maximum current efficiency of 0.26 cd/A were achieved. The CIE coordinate of EL spectra at 12 V was (0.35,0.37), close to the standard white light (0.33,0.33).In Chapter 9,2,1,3-benzothiadiazole (BTDZ) and 4,7-bis(thiophen-2-yl)-2,1,3-benzothiadiazole (BTBTDZ) were incorporated into the polyfluorene backbone to yield three new polymers bearing imidazole moieties in the side chains, with different fluorescence color. The fluorescence could be turned off by Cu2+ ions and then recover upon the addition of cyanide, making them good cyanide sensors with the detection limit down to 1.9μM. Moreover, by fully understanding this "turn-off-turn-on"'strategy and utilizing the cooperation of two polymers with different fluorescence color, the emission color of the mixture system of one of the imidazole-containing polymers and one from the corresponding polymers without imidazole ones, could be adjusted by the concentrations of the added copper and cyanide ions, leading to the output fluorescent signals diversity.