This dissertation, "Design, Synthesis and Studies of Novel Classes of Photochromic Spirooxazine and Diarylethene Ligands and Their Metal-to-ligand Charge Transfer Complexes" by Chi-chiu, Ko, 高志釗, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. DOI: 10.5353/th_b4389531 Subjects: Metal complexes - Synthesis Photochromism Ligands Ruthenium compounds - Synthesis

This dissertation, "Design, Synthesis and Studies of Novel Photochromic Zinc(II) Thiolate Complexes" by Tung-wan, Ngan, 顏冬芸, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Abstract of thesis entitled DESIGN, SYNTHESIS AND STUDIES OF NOVEL PHOTOCHROMIC ZINC(II) THIOLATE COMPLEXES submitted by Ngan Tung Wan for the degree of Master of Philosophy at The University of Hong Kong in August 2004 A series of diarylethene-containing diimine ligands was designed, synthesized and incorporated into the zinc(II) dithiolate system. The zinc(II) diimine dithiolate system was chosen in view of its well-known intense ligand-to-ligand charge transfer (LLCT) luminescence in the visible region. All the ligands and complexes were characterized by H NMR spectroscopy, positive FAB- or EI-mass spectrometry and gave satisfactory elemental analyses. The X-ray crystal structure of two of the zinc(II) dithiolate complexes were also determined. The novel phenanthroline-based dithienylethene zinc(II) complexes 1a-1c and 2a-2c displayed low-energy absorption shoulders at ca. 382 nm, tentatively assigned as ligand-to- ligand charge transfer [LLCT, р (SR) → π*(L)] transitions. Another series of zinc(II) diimine complexes, 3a-3c, containing dithienylene-based dipyrido[3,2- a:2'',3''-c]phenazine ligand showed a broad low-energy absorption band at ca. 420 nm, assigned as a mixture of ligand-to-ligand charge transfer [LLCT, р (SR) → π*(dppzL1)] and intraligand [IL, π(dppzL1) → π*(dppzL1) or n → π*(dppzL1)] transitions. Upon UV excitation at ca. 313 nm, zinc(II) complexes 1a-1c underwent photocyclization reaction, leading to the formation of a new absorption band in the UV region and two moderately intense absorptions in the visible region. The significant bathochromic shift of the absorption maxima corresponding to their open forms was mainly due to the formation of the closed forms, resulting in the increase in the extended π-conjugation across the condensed thiophene rings. In contrast to UV-induced photocyclization, excitation into the absorption bands of the closed form in the visible region resulted in the photochromic backward reaction. The absorption bands of the closed form decreased in intensity, indicating the regeneration of the open form as a result of the photochromic backward reaction. Moreover, the quantum yields for both the forward and backward reactions were determined. The photophysical and electrochemical properties of both the open and closed forms were also studied. Interesting switching of the luminescence and electrochemical properties of the complexes 1a-1c and 2a-2c induced by the photochromic reactions was demonstrated. The UV-visible absorption spectra of the free ligand (dppzL1) as well as complexes 3a-3c did not show any spectral change upon photo-irradiation at any wavelength. This indicated that the corresponding ligand and complexes are photochemically inactive, which could be explained by the inefficient π- delocalization between the C11 and C12 in the dppz moiety, in which the concerted π-bond rearrangement between C11-C12 and the thiophene units could not readily occur with light excitation. The luminescence and electrochemical properties of the free ligand (dppzL1) and its zinc(II) dithiolate complexes 3a-3c were also described. Upon excitation of the ligand and complexes at λ > 350 nm in degassed benzene solution, intense emissions at ca. 473 and 525 nm, respectively, were observed, which were assigned to originate from the respective IL

Photoswitchable molecular materials are of interest for optical data storage, optically controlled electronics, and light-controlled molecular machines or 'smart' surfaces. A promising way to incorporate optical switchability into materials is by using organic photochromic molecules--which convert reversibly between two forms with light--as ligands in coordination complexes. This design allows for the intimate communication between ligand and metal such that light-induced photoisomerization may be used to modulate metal-based properties. Spirooxazines, photochromic systems that photochemically isomerize between nonconjugated ring-closed spirooxazine (SO) and highly conjugated ring-opened photomerocyanine (PMC) forms, were derivatized with aphenanthroline moiety to enable the binding of transition-metal ions. Two phenanthroline-spirooxazines, an indolyl derivative and an azahomoadamantyl derivative, were investigated in the context of chemical substitution and medium effects. The ring-opened PMC forms of the spirooxazines were characterized by solid- and/or solution-state methods to extract the relative contributions of the canonical quinoidal and zwitterionic resonance forms to their molecular structure. The PMC form of the azahomoadamantyl derivative was found to exhibit significant zwitterionic character, with demonstrated sensitivity to medium polarity. The pronounced zwitterionic character was correlated with the high stability of the PMC form, high photoresponsivity, and slow thermal relaxation rates in this class of spirooxazines. The relative ligand field strengths of the SO and PMC forms of the two phenanthroline-spirooxazines were analyzed using the FT-IR and 13C NMR carbonyl signals of their molybdenum-tetracarbonyl-spirooxazine complexes. Differences in metal-ligand bonding in the SO and PMC forms were also investigated by a density functional theory fragment molecular orbital analysis. The SO form was found to be a better n-acceptor both empirically and theoretically. Lastly, the spirooxazine ligands were incorporated into electronically bistable cobalt-dioxolene redox isomers, where the low-spin-CoIII/high-spin-CoII equilibrium is sensitive to ligand field strength. Using solution-state spectroscopic methods, it was shown that the redox state of the cobalt centre could be modulated through photoisomerization of the spirooxazine ligand. As changes in cobalt redox state are associated with changes in magnetic spin state, this system forms the basis for a room-temperature photomagnetic material and highlights the powerful role of photochromic phenanthroline-spirooxazineligands in developing photoswitchable multifunctional materials.

This dissertation, "Design, Synthesis, Photophysics and Photochromic Study of Dithienylethene-containing N-heterocycles and Their D8 and D10 Metal Complexes" by Ka-wai, Lee, 李家偉, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: DOI: 10.5353/th_b3955840 Subjects: Photochromism Photochemistry Metal complexes - Synthesis

This dissertation, "Design, Synthesis, Luminescene and Photochromic Studies of Dithienylethene-containing Nitrogen and Mixed Nitrogen-oxygen Donor Ligands and Their Complexes" by Ho-man, Lee, 李浩文, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. DOI: 10.5353/th_b4175789 Subjects: Ethylene compounds - Synthesis Organic compounds - Synthesis Photochromism Photochemistry Ligands