The Design, Synthesis And Optoelectronic Properties Of The Novel Carbazole Derivatives With Non-conjugated Connection

The carbazole is a classical aromatic heterocyclic organic compound. Due to thenitrogen atom with the lone-pair electrons and the stable rigid planar-conjugatestructure, the carbazole can not only be substituted in different sites, but also exhibitsthe excellent light/thermal stability and optoelectronic properties. It is considered tobe a good electron-rich modified group. The materials containing the carbazolegroup or the derivatives based on the carbazole structure are widely used in manyfields, including medicine, dyestuff, sensor, electroluminescent and photovoltaicdevices. Based on the carbazole, it can be found more feasible options on synthesiswith maintaining their special physical and chemical properties. The most commonway to use the carbazole group is introducing it into the backbone or side-chains byconjugate link. Such a structure will bring the well intramolecular conjugation andcharge transfer capability. But it had proved that the non-conjugated connectionbetween the carbazole and side-chains can also take some outstanding electronicproperties. By means of the dense electron distribution and the close packing of thefunctional groups, the charges can be efficiently delivered by hopping between thecarbazole groups (e.g. polyvinylcarbazole/PVK). Meanwhile, the periphery locationof carbazoles and the lone-pair electrons are benefit for the ions detection and madethe derivatives to be the potential candidates in the sensor area. However, there are few works on the optical and electrical properties of the materials withnon-conjugated carbazole connection. In this thesis, we will design and synthesizethe novel carbazole derivatives grounded on this unusual structure, characterize theirphysical and chemical properties and deeply study the influence of thisnon-conjugated connection structure.Above of all, we design and synthesize six small molecules by the Suzukicoupling reactions. They have the same mainchains or backbones and the differentside-chains, with and without the carbazole. The results of thermodynamiccharacterization prove that the introduction of carbazole at the end of side-chains canimprove the thermal stability of these materials effectively. The spectroscopiccharacterization shows the absorption peaks move to the long-wavelength regiongradually followed by the content of heteroatoms increasing in the backbone. And it isalso accompanied with the shifting of fluorescence emission from blue to red.Although the adding of carbazole cannot give any obvious effect on the solutionphotoluminescence, it would improve their fluorescence quantum yields in solutions.Among these materials, the OCZ which has eight carbazole groups located at theperipheral area exhibits the highest fluorescence quantum yields, as high as98%.Based on these materials, we attempt to use them to detect the different ions. Inthe fluorescent sensor tests with metal ions, by comparing the performances in andbetween these material groups, we found the present of carbazole is benefit for thedetection of iron ions (Fe3+) and copper ions (Cu2+). The increase in the number ofcarbazole groups in the molecule can significantly enhance the sensitivity andselectivity. Among them, OCZ shows the best performance in fluorescence detectionof Fe3+. Its fluorescence quenching constant can be comparable with many othersensor materials for iron that have been reported. We propose that the goodperformance is caused by the electron-rich property and wide detection range of theperipheral carbazole structure. We also study the sensor properties of OCZ withdifferent anions, and the results show that it possesses the remarkable sensitivity andselectivity on the fluorescent quenching detection for iodide ions (I-). Thefluorescence quenching constant of OCZ for I-is over eight orders of magnitude (108). The results of comparative experiments between OCZ and PFO demonstrate that thegood performance primarily arises from the introduction of peripheral carbazole.Moreover, OCZ also reveals the excellent colorimetric sensing property for I-. Inaddition to the ideal detection limit and selectivity, the detection speed is very fast. Itcan give an immediate response even under a low ion concentration condition and canbe vested in the real-time detection. Taking both sensitivity and sensing rate intoaccount, the performances of OCZ satisfy the requirements of practical application.The subsequent competition experiments and real-world water sample experimentsfurther prove its detection capabilities of I-in the complex systems. We believe thatthis novel fluorometric/colorimetric probe material has great potential for the I-detection in the real environment.Simultaneously, we utilize another non-conjugated connection derivativeTCTBC in the organic heterojunction photovoltaic field. The carbazole derivative isused as the donor material and the devices are fabricated by spin-coating and vacuumevaporation. The parameters of the preparation process are optimized in detail, suchas the species of acceptor and solvent, the ratios of donor and acceptor, the thicknessof the active layer, and some device processing methods. The studies on the thermalannealing and process additives reveals that adjusting the morphology of active layersin the nano-scale can finally affect the photoelectric conversion efficiency (PCE) ofthe photovoltaic devices. The experimental data prove that the device can reach thebest efficiency only when balancing the effective charge separation of photoinducedexcitons and the charge transfer capability inside the device. In this TCTBC smallmolecule system, the influence of the charge transfer is obviously higher than thecharge separation which would be due to its smaller molecular volume and the lowercharge mobility. At last, the best PCE of device made by this material is achievedunder the annealing treatment, and an ideal open circuit voltage which approaches tothe theoretical value is obtained, over1V. Finally, we compare the photovoltaicproperties of TCTBC with its analogue which without the peripheral carbazoles, andthe results reveal that the device performances are slightly better without thecarbazoles. Analyzing from the light absorption, charge transfer and the nano-scale morphology, we can speculate that the presence and aggregation of the rigidcarbazoles located at the side-chains terminal may interrupt the continuity of theacceptor network in the active layer. This change can consequent obstruct the chargeconduction, and to the disadvantage of the device performance. But at the same time,we also prove that the aggregation of carbazole groups is separated from theaggregation of the backbones by the flexible non-conjugated connection. If continueto research these materials containing the non-conjugated connection, the moreefficient material systems with multiphase aggregation may be developed.