The synthesis of useful chiral skeletons from simple achiral starting materials is always the dream of organic chemists. In the past decades, organocatalysis has been rapidly developed and has become one of the most important methods in asymmetric catalysis. The aim of this thesis is to develop asymmetric methods for the construction of useful chiral skeletons based on organocatalytic chemistry. Many natural products and biologically important compounds contain the hydrogenated dibenzofuran (Figure 1) as a common sub-structure. In the first part of this thesis, the first amine-catalysed asymmetric synthesis of a dihydrodibenzofuran species from bisenal substrates has been demonstrated. After a systematic screening of various reaction parameters, the optimal conditions have been found to be as follows: 0.1 M of substrate in solution with toluene with 0.2 equiv of (S)-di(2-naphthyl)pyrrolinol TMS ether (C2.8) and 0.2 equiv of 2-nitrobenzoic acid at 50 ℃ for 7 h under an argon atmosphere (Scheme 1). The first step product, an aldehyde, can be reduced in one pot to an alcohol by NaBH4. This two-step protocol gives exclusive cis selectivity. Many chiral cis-dihydrodibenzofuran species have been synthesized from the corresponding bisenal substrates in moderate to good yield with good to excellent ee (Scheme 1). The resulting cis-dihydrodibenzofuran species have promising synthetic applications. As shown in Scheme 2, the less hindered face of the newly formed C ring is more reactive and highly regioselective functionalizations of the C ring have been achieved. In the second part of this thesis, the first asymmetric aziridination of trans-α-nitroalkenes via a phase-transfer catalysis strategy has been systematically studied. The chiral phase-transfer catalysts screened are derivatives of the cinchona alkaloids. The new cinchonidine-derived phase-transfer catalyst CD17 has been found to be optimal for the aziridination (Figure 2). Addition of a small amount of water is crucial to achieve complete conversion of the reaction. Both trans-1-nitro-2-arylalkenes and trans-1-nitro-2-alkylalkenes are suitable substrates (Scheme 3). The reaction can be run on the gram-scale without significant loss of efficiency and ee. Mechanistic studies have revealed that the aziridination proceeds through an aza-Michael addition followed by an intramolecular SN 2 type three-membered ring formation (Scheme 4). / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

New classes of luminescent transition metal complexes, including the systems of rhenium(I) tricarbonyl diimine, cyclometalated iridium(III) diimine, cyclometalated rhodium(III) diimine, ruthenium(II) diimine and ruthenium(II) terpyridine complexes tethered with rhodamine moieties, have been synthesized. The X-ray crystal structure of one of the cyclometalated rhodium(III) diimine complexes with rhodamine pendants, [Rh(SPLC2N2)(ppy)2](PF6) has been determined. The molecular structure of [Rh(SPLC2N2)(ppy)2](PF6) showed a distorted octahedral geometry and the rhodamine moiety was found in a spirolactam closed-ring form. All of them were found to exhibit emission in fluid solution. The emissions of rhenium(I) tricarbonyl diimine and ruthenium(II) polypyridyl complexes are derived from the triplet metal-to-ligand charge transfer (3MLCT) excited state, i.e. from dπ orbital of the rhenium(I) or ruthenium(II) metal center to the π* orbital of the diimine ligand; while that of cyclometalated iridium(III) diimine complexes is (3MLCT) [dπ(Ir) → π*(N^N)] and that of cyclometalated rhodium(III) diimine complexes involves the (3IL) [π → π*(N^C)] excited state, probably mixed with (3MLCT) [dπ(Rh) → π*(N^C)] character. The cation-binding properties of these complexes toward alkali, alkaline-earth and transition-metal cations were investigated by electronic absorption and emission spectrophotometries. Some of them were found to exhibit new low-energy absorption and emission bands, characteristic of the rhodamine absorption and emission, with high selectivity and sensitivity for certain transition metal cations. A series of rhodamine-appended Schiff base organic compounds has also been synthesized in order to explore their capability as luminescent lanthanide ion sensors. The lanthanide ion binding properties of one of the compounds in acetonitrile were examined. Upon addition of lanthanide ions, new intense low-energy electronic absorption and emission bands were also observed, characteristic of the rhodamine absorption and emission, demonstrating its lanthanide ion sensing behaviour. / published_or_final_version / Chemistry / Master / Master of Philosophy

The research on asymmetric organocatalysis has been intensifying since the beginning of 2000. The growing interest in this research area is driven by the importance of the chemical synthesis of enantiomerically pure products. While the general field of asymmetric organocatalysis has been explored intensively, the recyclability of organocatalysts has not really been considered. The attachment of phosphonium ion phase tags to chiral binaphthyl-based phosphoric acid catalyst and the use of these materials in a range of organocatalytic asymmetric Friedel-Crafts reactions of indoles have been studied. Placement of tags at the 3 and 3’ positions of the binaphthyl core, so that they could serve as steric blocking groups, failed to produce an active catalyst. However, moving the phosphonium ion groups to the 6 and 6’ positions produced an efficient and enantioselective catalyst. Aided by the presence of the phase tags, the chiral catalyst was easily recovered at the end of the reactions, and could be reused several times, albeit with somewhat decreased efficiency and enantioselectivity. Furthermore, the synthesis of 1,1’-spirobiindane-7,7’-diol and their spiroindane-based derivatives have been explored. The (R)-1,1’-spirobiindane- 7,7’-diamine was successfully applied in exo selective asymmetric Diels-Alder reactions of -unsaturated aldehyde with cyclopentadiene. However, moderate results aspire further studies in assay of (R)-1,1’-spirobiindane-7,7’-diamine derivatives, which bear various bulky groups at the 6 and 6’ positions. Moreover, the conversion of the SPINOL into a spiroindane ketone unfortunately failed, which was caused by the sterically crowded structure of the SPINOL skeleton. / published_or_final_version / Chemistry / Master / Master of Philosophy

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

A series of alkynylplatinum(II) polypyridine complexes with 4,4′,4′′-tricarboxy-2,2′:6′,2′′-terpyridine and 4,4′-dicarboxy-2,2′-bipyridine as TiO2 anchoring functionalities, has been successfully synthesized. Their photophysical, electrochemical and luminescence properties have been extensively studied. The excited state properties were probed using nanosecond transient absorption spectroscopy. [Pt(tctpy)(C≡C-Th-BTD-Th)][NnBu4]2 displayed a long-lived transient signal which was tentatively assigned to result from the formation of a charge-separated state, which could be alternatively described as a [Pt(tctpy)???(C≡C-Th-BTD-Th)+?] state, with the charge recombination rate constant determined to be 2.9 × 105 s?1. The excited state redox potentials for the oxidation process were determined and the data confirmed the ability of the complexes to inject an electron into the conduction band of TiO2. The majority of the complexes were found to sensitize the nanocrystalline TiO2 and exhibit photovoltaic properties, which have been characterized by current-voltage measurements under illumination of air mass (AM) 1.5G sunlight (100 mW cm–2). A new class of molecular dyads comprising metalloporphyrin-linked alkynylplatinum(II) polypyridine complexes was synthesized and characterized. Their photophysical, electrochemical and luminescence properties have been studied in detail. The excited state properties were probed using nanosecond transient absorption spectroscopy which indicated the formation of a charge-separated state involving the porphyrin radical anion, [Por??－(C≡C)Pt+?]. The excited state redox potentials for the oxidation process were also determined with the data supporting the capability of the complexes to inject an electron into the conduction band of TiO2. The majority of the complexes were found to sensitize the nanocrystalline TiO2 and exhibit photovoltaic properties, as characterized by current-voltage measurements under illumination of air mass (AM) 1.5G sunlight (100 mW cm–2). A series of organic materials consisting of a triphenylamine-based donor with oligothiophene or oligothienylenevinylene based-conjugated linker and dicyanovinyl, tricyanovinyl or cyanacrylic acid groups as acceptor, was synthesized and characterized. Their photophysical, electrochemical, thermal and luminescence properties were studied. Transient absorption spectra of TPA-OTV-DCN in dichloromethane solution on the pico- to nanosecond timescale were recorded after femtosecond laser excitation at 400 nm. A transient signal at ca. 700 nm was tentatively assigned to result from the formation of a charge-separated [(TPA-OTV)+??DCN??] state with the charge recombination rate constant determined to be 5.3 × 109 s?1. The energy levels of the LUMOs of TPA-OTV1-DCN, TPA-OTV2-DCN, TPA-OTV3-DCN TPA-TAZ1-DCN, TPA-TAZ2-DCN and TPA-o-4Th-DCN were calculated to be of ca. ?3.9 eV, establishing the formation of a downhill driving force for the energetically favorable electron transfer process involving the injection of an electron into the LUMO of the C60 acceptor. The majority of the compounds were found to exhibit photovoltaic properties. The photovoltaic responses were characterized by current-voltage measurements under illumination of air mass (AM) 1.5G sunlight (100 mW cm–2). / published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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published_or_final_version / Chemistry / Doctoral / Doctor of Philosophy

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