A series of photochromic dithienylethene-containing triarylboranes has been synthesized and characterized. The X-ray crystal structure of (4,5-bis(2,5-dimethylthiophen-3-yl)-thiophen-2-yl)dimesitylborane has been determined. An intense electronic absorption band was observed in all the triarylborane-containing compounds, corresponding to the intramolecular charge-transfer transition from the π-conjugated thiophene / fused thiophene / bithiophene to the vacant pπorbital of boron. This class of compounds was also found to bind fluoride ion such that the trigonal planar geometry of the boron center would be changed to tetrahedral, leading to a significant perturbation in the photophysical properties. Upon photo-excitation into the transition band, (4,5-bis(2,5-dimethylthiophen-3-yl)-thiophen-2-yl)dimesityl- borane and (4,5-bis-(2,5-dimethylthiophen-3-yl)-thieno[3,2-b]thiophen-2-yl)- dimesitylborane displayed multi-addressable photochromic reactivities upon addition of fluoride, in which a green solution was found in the closed form of the unbound compounds, while they changed to a purple color upon fluoride binding. Interestingly, both (4',5'-bis(2,5-dimethyl-thiophen-3-yl)-2,2'- bithiophen-5-yl)dimesitylborane and (4',5'-bis(2,5-dimethyl-thiophen-3-yl)-2,2'- bithiophen-3-yl)dimesitylborane displayed gated photochromic reactivities upon addition of fluoride, while only typical photochromic reactivity was observed in (4',5'-bis(2,5-dimethyl-thiophen-3-yl)-2,2'-bithiophen-4-yl)- dimesitylborane, indicative of a strong influence of the substituent effect on the photochromic reactivity upon incorporation of the -BMes2 group. A series of photochromic dithienylethene-containing β-diketones and the corresponding boron(III) compounds, appended with -BF2, -B(C6F5)2 and -BPh2, have been designed and synthesized. Upon photo-excitation into the transition band, typical photochromism was observed in all the dithienylethene- containing β-diketone ligands with the color changed from pale yellow to green in degassed benzene solution. Upon incorporation of the -BF2 and -B(C6F5)2 groups, near-infrared responsive photochromic behavior was observed, in which the absorption of the closed form was found to be at ca. 758-863 nm, suggesting that a pronounced perturbation of the dithienylethene was achieved by coordination of the boron(III) center. Moreover, a significant reduction in luminescence intensity of over 90 % was observed upon photocyclization, indicative of their potential application as photoswitchable luminescence materials. The thermal stability of the closed form and the activation energy for the thermal cycloreversion have also been studied on the representative compounds, 1-(4,5-bis(2,5-dimethylthiophen-3-yl)thiophen-2- yl)-butane-1,3-dione and difluoroboryl(1-(4,5-bis(2,5-dimethylthiophen-3-yl)- thiophen-2-yl)butane-1,3-dionate). A series of photochromic dithienylethene-containing BODIPY has been successfully prepared and characterized. The electronic absorption properties have been studied. These compounds showed an intense visible absorption band, corresponding to the 0-0 band of a strong S0→S1 transition of the BODIPY core, with a weak and broad absorption band at higher energy, corresponding to the S0→ S2 transition of the BODIPY core. An absorption band in the UV region was also observed in 2,3-bis(2,5-dimethyl- thiophen-3-yl)thiophene-containing derivatives, corresponding to the π→π* transitions of the dithienylethene moiety. The photochromic reactivities have also been studied such that the photostationary state was found to be reached upon irradiation in the UV region for over eight hours, while no observable changes would be obtained upon photo-excitation in the visible region. The slow conversion rate has been suggested to be attributed to the fact that a rapid excitation energy transfer could occur from the excited Th-DTE to the BODIPY moiety, rendering the suppression of the photocyclization. / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

At the end of this thesis, the 1H and 13C {1H} NMR spectra of all the new compounds are listed in the Appendix. / Chapter 1 presents an overview of BODIPYs, including their general synthesis, properties, reactivities, and applications. The use of these compounds as photosensitizers for photodynamic therapy and fluorescent sensors for metal ions is highlighted. / Chapter 2 reports the synthesis, spectroscopic characterization, photophysical propreties, and in vitro photodynamic activities of a series of symmetrical distyryl BODIPYs substituted with one to five hydrophilic oligoethylene glycol monomethyl ether chain(s). In general, these compounds are essentially non-aggregated in DMF, resulting in a strong fluorescence emission and relatively high efficiency in generating singlet oxygen. Being formulated with 0.05% Tween 80, these compounds act as efficient photosensitizers. The compound which contains five triethylene glycol monomethyl ether chains exhibits the highest photocytotoxicity with an IC50 value as low as 7 nM toward HT29 human colorectal carcinoma cells. The high photodynamic activity of this compound can be attributed to its high efficiency in generating singlet oxygen, low aggregation tendency, and high cellular uptake. In addition, this compound also has a strong and selective affinity to the endoplasmic reticulum of the cells, causing cell death mainly through apoptosis. / Chapter 3 reports a related study on a series of unsymmetrical distyryl BODIPYs. These compounds possess three triethylene glycol monomethyl ether chains and another substituent at the other styryl group. The effects of this substituent on the photophysical properties, aggregation behavior, cellular uptake, and subcellular localization have been explored. Furthermore, their in vitro photodynamic activities have also been evaluated and compared with those of symmetrical analogues reported in Chapter 2. / Chapter 4 describes a novel ratiometric near-infrared fluorescent dye based on distyryl BODIPY with a 4-dimethylaminophenylethynyl group at the 2- and 6-positions. This compound exhibits a remarkable blue-shift in its absorption and fluorescence emission positions upon protonation with trifluoroacetic acid in organic solvents or HC1 in water in the presence of 0.05% Tween 80. These changes can be made reversible upon addition of a base. / Chapter 5 describes two monostyryl BODIPYs which contain two or four water-soluble amide chains as the metal chelators. The photophysical properties of these compounds and their spectral response to various metal ions have been investigated. The results show that the compound with two amide chains can detect Zn2+ ion in MeCN. They bind in a 1:1 stoichiometry with a binding constant of 2.2 x 104 M-1 . The fluorescence emission increases remarkably in intensity and shifts substantially to the blue from 620 to 572 nm due to the inhibition of the intramolecular charge transfer. The compound which contains four amide chains can detect Cd2+ ion with a high selectivity in phosphate buffered saline. / Chapter 6 reports the synthesis and spectral properties of a silicon(IV) phthalocyanine with two axial bis(2-picolyl)amine moieties which act as the binding sites for metal ions. The effects of various metal ions on its absorption and fluorescence spectra have been examined. The results indicate that this compound shows a relatively high sensitivity to Zn 2+ ion. Moreover, the proposed binding mode and the sensing mechanism are also discussed. / This thesis describes the synthesis and characterization of several series of functional boron dipyrromethenes (BODIPYs) and a silicon(IV) phthalocyanine. Their applications as efficient photosensitizers in photodynamic therapy and selective fluorescent sensors for metal ions are also reported herein. / He, Hui. / Adviser: Dennis Kee Pui Ng. / Source: Dissertation Abstracts International, Volume: 73-02, Section: B, page: . / Thesis (Ph.D.)--Chinese University of Hong Kong, 2010. / Includes bibliographical references. / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [201-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstract also in Chinese.

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