One of the main objectives of this thesis was the synthesis of new chelating ligands containing a photochromic unit able to change its conformation upon light irradiation. This isomerization should serve to modify the magnetic behavior of the new coordination compounds, formed upon reaction of transition metals or lanthanides, assembled within the phtochromic ligands. Whith these aims, the synthesis of 5 new ligands has been achieved, which have been characterized successfully. Subsequently, the preparation of 22 coordination compounds with these ligands has been accomplished. The crystallographic study of these coordination compounds has been very important for the complete understanding of the magnetic and photohromic properties. Regarding the crystal structures, in Chapter 1, the distinct photochromic properties of the complexes discussed was rationalized in light of the structural information. The results show that crystal design may constitute an interesting way for modulating the properties of the solid state photoactivity. Two new ligands were synthesized in Chapter 3, based on beta diketone moieties, which additionally, are functionalized with a phenol group. Those groups together form an excellent chelating pocket to introduce metal arrays. Importantly, those arrays can be formed as pair of heterometallic dimers, whose ground state exhibit in some cases S=1/2 systems, thus providing a pair of spins ư well defined within the molecule. This feature can be exploited in the context of quantum computing by studying the quantum coherence of these spin. Indeed, coherence times of thousands of nanosecond can be measured at low temperature. Two other new ligands, have been presented in Chapter 4. These have been synthesized via Schiff base condensation. Similar two the beta diketones, these ligands are able to perform fast and excellent photochromism, in addition to the cis/trans isomerizations that can undergo themselves. While those isomerizations have not been studied, they could be used as gate-reactivity, adding more versatility to these compounds. The chelating pockets of these ligands are very useful regarding to the coordination ability with lanthanides and transition metals. Single molecule magnet behavior has been observed in a dysprosium cluster. Finally, in Chaper 5, the synthesis of a new photochromic ligand containing a pyridine-pyrazole moiety, has been tested for the preparation of a Fe(II) spin crossover helical system. This has shown to be a good candiadate as part of new hybrid devices, because the excellent resistance to the fatigue, the different fluorescent behavior and the SCO features.

The crystal chemistry of spin crossover (SCO) behavior in coordination compounds can potentially be in association with smart materials—promising materials for applications as components of memory devices, displays, sensors and mechanical devices and, especially, actuators, such as artificial muscles. This Special Issue is devoted to various aspects of SCO and related research, comprising 18 interesting original papers on valuable and important SCO topics. Significant and fundamental scientific attention has been focused on the SCO phenomena in a wide research range of fields of fundamental chemical and physical and related sciences, containing the interdisciplinary regions of chemical and physical sciences related to the SCO phenomena. Coordination materials with bistable systems between the LS and the HS states are usually triggered by external stimuli, such as temperature, light, pressure, guest molecule inclusion, soft X-ray, and nuclear decay. Since the first Hofmann-like spin crossover (SCO) behavior in {Fe(py)2[Ni(CN)4]}n (py = pyridine) was demonstrated, this crystal chemistry motif has been frequently used to design Fe(II) SCO materials to enable determination of the correlations between structural features and magnetic properties.

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

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