Synthesis And Properties Of Carbazole Modificatied Phenanthroimidazole And Benzothiadiazole

Carbazole as heterocyclic compounds containing nitrogen atom, exhibit excellentoptical and electrochemical properties, not only on the material of the electrons andholes transfer ability has enhanced effect, but also can improve materialelectrochemical stability and thermodynamic stability. Dendrimers modified withcarbazolecan largely reduce the phenomenon of ACQ because of dot separation effect.and improve the molecular fluorescent efficiency. Molecules containingphenanthroimidazole and benzothiadiazole are good electron acceptors used asbuilding block to construct π-conjugated functional organic materials. This thesisdesigned a series phenanthroimidazole and benzothiadiazole derivatives modifiedwith carbazole at terminal, studied their nature of OLED and the fluorescent sensor.Innovative research results obtained are summarized as follows:1. we synthesized new phenanthroimidazole derivatives bearing terminalcarbazole linked by different spacers, including1,4-phenylene, phenylvinyl andphenylvinylcarbazolylvinyl (PSC, PDC, PCC), and bearing terminal pyrene (PPP),which exhibited excellent solubility in common organic solvents. It was found that theobtained phenanthroimidazole derivatives were high emissive in cyclohexane, forexample, the fluorescence quantum yields were0.72and0.83for PSC and PCC,respectively, using quinine sulfate (0.1N in H2SO4) as a standard. Meanwhile, theyexhibited high thermal stability with initial decomposition temperature over450°C,which might be helpful for improvement of the device stability and lifetime. Theorganic light-emitting diodes with the configuration of ITO/NPB (45nm)/phenanthroimidazole derivatives (15nm)/TPBI (40nm)/LiF/Al, in which PSC, PDC,PCC and PPP as the emitting materials, were fabricated. The device based on PSCgave a saturated blue emission with CIEx,yof (0.16,0.17), and the turn-on voltage,maximum luminance and power, current efficiency of the device were of3.40V,1190cd/m2,0.85lm/W and0.92cd/A, respectively. The device based on PDC and PCC showed similar performance besides the color of the emitting light. Therefore, thephenanthroimidazole derivatives might become candidates as emitting materialsemployed in OLEDs, and other related fields.2. The new sensory material based on the nanofibrils fabricated fromPhenanthroimidazole derivatives have been afforded for the detection of TFA vaporsefficiently. It has been found that the fluorescence emission of the nanofibrils can bequenched or shift to long wavelength quickly and significantly upon exposure to TFAvapor. Notably,taking PCC as an example, the response time is ca.0.1s in organoglefilm while the response time is ca.1.86s in thin film. the response time is ca.0.6s inorganogle film and ca.0.2s for PSC and PDC,which exhibits faster fluorescentresponse in milliseconds and higher sensitivity than thin film towards gageous TFA.We suggest that the high sensitivity and fast response of the sensory nanofibrilstowards gaseous TFA may come from the high surface-to-volume ratio and largeinterspace in the nanofibril-based networks, which favor the enhanced adsorption,accumulation and diffusion of gaseous molecules.Linear Stern–Volmer plots wereobtained from the fluorescence quenching titration profiles and calculatedStern–Volmer binding constants (KSV) was32520M-1for PCC, the detection limit forcompound PCC towards TFA was measured to be0.92×10-7mol/L,Stern–Volmerbinding constants (KSV) was41795M-1,56695M-1for PSC, PDC. the detection limitfor compound PCC towards TFA was measured to be0.92×10-7mol/L.0.72×10-7mol/L,0.53×10-7mol/L for PSC and PDC, respectively. In the sensing cyclestest,the fluorescent emission wavelength shift from484nm to552nm, So the bluefluorescence turns rapidly into a yellow fluorescent treated with TFA Vapor,which it isgood for naked detection,which will be helpful in the design of novel fluorescencechemosensors with a high performance.3. New branched benzothiadiazole-cored conjugated oligomers with terminalcarbazoles1and2have been synthesized. It was found that very weak p-p stackingoccurred in the solid states on account of site isolation effect of the branchedarchitectures, and the films based on oligomers1and2could emit strong red light.Interestingly, the fluorescence emission intensities of1and2in the films decreasedobviously when exposed to gaseous TNT and DNT. The fluorescence quenchingefficiencies of the films based on oligomers1and2were42%and91%, respectively,when exposed to saturated vapor of DNT for3min at55°C. The high sensitivity of2 compared with1was mainly due to its strong electron donating ability. In addition,we found that the fluorescence lifetime of2decrased after addition of DNT in THF.Combined with the linear Stern-Volmer plots, we deduced that the fluorescenceresponse of branched benzothiadiazole oligomers towards DNT and TNT was resultedfrom photo-induced electron transfer. Therefore, the branched benzothiadiazole-coredoligomers bearing carbazole units could be used as fluorescence sensors towardsgaseous nitroaromatics-based explosives.