| dc.description.abstract | Three model compound systems are designed and successfully synthesized in this thesis. The first system contains the benzothiadiazole structural unit. The second system is composed of the quinoxaline structural unit, and the third system is constructed based on the benzothiazole structural unit. We have measured the linear and nonlinear optical properties of these compounds. Some features are found about the relationship between molecular structure and optical properties and can be listed as follows:
1. For the first series of model chromophores, the structure based on D-π-A-π-D has lead to good quantum yield. The insertion of C-C triple bond into the conjugation has resulted in a red-shift of fluorescence. Also, this insertion of triple bond was found to have positive impact to two- and three-photon efficiencies. On the other hand, diphenylaminofluorenyl is a better electron-donor for the promotion of multiphoton efficiencies compared to a triphenylamine group.
2. For the second series of model chromophores, the structure contains the units of quinoxaline which exhibt good quantum yield also. The addition of methoxy group into the central quinoxaline unit causes a blue-shift of fluorescence and a decrease of the two-photon efficiency. When the diphenylaminofluorenyl is attached by methoxy groups, it will lead to a red-shift of fluorescence and increase the two-photon efficiencies. While three-photon efficiencies does not work in the same way. On the other hand, when the C-C triple bond is inserted into the conjugation, it results in a red-shift of fluorescence. Also, the insertion of triple bond will improve the two-photon efficiencies but the three-photon efficiency does not show the same trend, neither.
3. From the third series of model chromophores, it is found that the addition of thiophene unit into the conjugated framework can promote both two- and three-photon efficiencies. Interestingly, the insertion of C-C triple bond decreases the two- and three-photon efficiencies of these model compunds. Compared to triazolopyridine unit, benzothiazole is a better eletron-acceptor which possesses large improvement on the two- and three-photon efficiencies.
Overall, if we desire to enhance the two-photon efficiencies, we can select 4,4′-dimethoxyfluorenylamine as the donating group, Thiophene or C-C triple bond as the π-bridge, and benzothiazole or quinoxaline as the acceptors. If we need to improve the three-photon efficiencies, we can utilize 4,4′-dimethoxyfluorenylamine as the donating group, thiophene as the π-bridge, and benzothiazole as the acceptors. Based on the current investigation, we suspect that the requirements for the molecular design toward enhanced two- and three-photon efficiencies should be intrinsically different. | en_US |