Design, Synthesis And Properties Of Novel Pure Organic Sensitizers

With the consumption of fossil energy, the increasing intensity of global warming, the excessive of greenhouse gas emissions and increasingly limited energy reserves, the development and use of renewable energy has been paid more and more attention. Currently, the medium for the development of solar is photovoltaic conversion, via solar cells. The dye-sensitized solar cells (DSSC) showed advantages over silicon solar cells. The sensitizers are the key point of dye-sensitized solar cells, and the capture of sunlight, the injection of excited electron into the semiconductor conduction band, are all accomplished by them. The efficiency of DSSC was determined by the structures of sensitizers. Due to its rarity of the precious metal in Ru-based sensitizers, large amounts of researches have been carried out on metal-free organic dyes.In this thesis, we have synthesized a series of new sensitizers and a new fluorescence chemosensors based the structures of D-ti-A. The main contents of thesis are described as follows:Chapter1. We introduced the concept and the species of renewable energy, the use of solar energy and the types of solar cells, the device structure, working principle of DSSCs. We also discussed the role of sensitizers in DSSCs, the sorts of sensitizers, and the star molecules in pure organic sensitizers.Chapter2. The phenomenon of ?-stacked aggregation on the TiO2electrodes always shortens the lifetime of excited electron, directly decreasing the electron injection greatly. Therefore, two4-tert-butylbenzene moieties were chosen as additional groups of triphenylamine, which can keep a certain distance between molecules, reflecting their function to prevent aggregation. The obtained results demonstrated that the introduction of tert-butyl groups may be able to play the anti-aggregation effect.Chapter3. Based on the idea of chapter2, we selected two tetraphenylethylene (TPE) moieties as additional groups in the donor part. The propeller-shaped moieties could establish a barrier to triiodide. There are eight phenyl rings in the two para-positions of triphenylamine, which should block the charge recombination to a certain degree, and the two introduced TPE units keep a defined distance between molecules, reflecting their function of reducing the level of intermolecular ?-? stacking. Through the absorption spectrum, chemical calculation results, and the role of adsorbent CDC A, we confirmed that the introduction of TPE can not only inhibit intermolecular aggregates, but also reduce the degree of charge recombination.Chapter4. The D-?-A structure sensitizers only contain one anchoring groups, offered one electron injection channel. The presence of only one anchoring functionality per molecule could represent a serious constraint with respect to Ru(II) sensitizers, where1to4anchoring groups are available for tunable interfacial electron transfer. Therefore, in order to study the relationship of the electron injection efficiency and the number of acceptors, we synthesized sensitizers with two acceptor groups, and the tert-butyl group was introduced into the sensitizers again, to inhibit the intermolecular aggregation. Based on the study of the photovoltaic performance of sensitizers, we can infer that the introduction of another anchoring group can indeed increase the electron injection efficiency and improve the photocurrent of the device. In addition, we have also verified the function of anti-aggregation of tert-butyl by the adsorbent CDCA.Chapter5. We synthesized2,3-disubstituted thiophene-based dipolar sensitizers, and selected two N, N-dihexyl-aniline units as the double donors attached to2,3-disubstituted thiophene. The introduction of two donors can lift the HOMO level of the molecule, red shift the absorption peak, increase electron-donating ability of the donor side and enhance the degree of intramolecular charge transfer. The obtained results demonstrated that the photovoltaic performances can be also affected by the structures of the conjugated bridges.Chapter6. We selected hexyloxy substituted benzothiadiazole and quinoxaline unit as auxiliary acceptor to develop D-?-A'-?-A configuration sensitizers. The introduction of auxiliary acceptor can optimize the energy level, narrow the energy gap of the sensitizers, increase its response in the long wavelength region and improve the stability of the sensitizers under irradiation. The results demonstrated that we can obtain the optimum combination for each part by the alternative of auxiliary acceptor groups and the ? units. For the stronger electron withdrawing ability of benzothiadiazole and the electron delocalization property of thiophene, the sensitizer based on them showed the highest power conversion efficiency. Chapter7. Based on the quinoxaline unit, we optimized its structure and developed a new auxiliary acceptor,11,12-Bis(hexyloxy) dibenzo[a,c]phenazine (BPz). BPz unit was composed of a completely coplanar fused ring and two hexyloxy. The light harvesting ability, charge transfer and solubility of the sensitizers can be facilitated by the introduction of BPz. Therefore, we set BPz unit as auxiliary acceptor,3-hexylthiophene as ? unit, synthesized a series of D-?-A'-?-A sensitizers. By changing the electron-donating ability of donor, the energy levels of sensitizers can be adjusted again to obtain the highest power conversion efficiency.Chapter8. From the results of chapter7and chapter8, in D-?-A'-?-A sensitizers, we can infer that the efficiency of them is determined by the structural modifications of auxiliary acceptor. Thus, in this chapter, we focus on the effect of the introduced different auxiliary acceptor in molecules. We selected two different electron withdrawing groups, quinoxaline unit and benzoxadiazole unit, with unequal abilities of electron-withdrawing, incorporated into the conjugated bridge to further develop new D-?-A'-?-A configuration sensitizers. The result implies that not only broad absorption spectrum but also suitable energy levels are essential to high performance DSSCs.Chapter9. Recently, thieno[3,4-c]pyrrole-4,6-dione (TPD) based conjugated copolymers have been intensively investigated for their applications in polymer bulk heterojunction solar cells. However, TPD-based sensitizers for DSSCs were very rare. Therefore, in this chapter, we synthesized a series of D-?-A'-?-A sensitizers containing TPD unit as auxiliary acceptor, and discussed the properties of the sensitizers, and studied their photovoltaic performance systematically. Chapter10. Hypochlorous acid is one of the reactive oxygen species in living cells, and plays critical roles in the immune system. In this chapter, we present a simple method to detect hypochlorite (OC1) with high selectivity and sensitivity, by utilizing the oxidative deoximation reaction of luminescent oxim (1,"on") to its corresponding nonluminescent aldehyde (2,"off")-The obtained results demonstrated that the utilization of the controllable adjustment of the electron-withdrawing ability of the acceptors linked to a luminophore in the presence of some analytes, accompanying with the changed fluorescent signal from " on" to "off", might be a good approach to develop many new chemosensors with good performance.