http://dspace.cityu.edu.hk:80/handle/2031/728 2013-06-15T02:14:34Z http://dspace.cityu.edu.hk:80/handle/2031/6897 Title: Spectroscopy and energy transfer in metal ion doped glasses Authors: Wen, Hongli (溫紅麗) Abstract: This thesis had three major aims. The first one was to investigate the effect of the dielectric medium upon the spontaneous emission rate using tripositive europium ion-doped lead borate glass. The second aim was to investigate the spectral properties of metal ion-doped glass. The dopant ion was a lanthanide ion or transition metal ion. The host glasses were lead borate glass and sodium borosilicate glass. The third aim was to study the luminescence properties and energy transfer process between ions doped into these glasses. The dopant ions were lanthanide ions or lanthanide-transition metal ion pairs. The following describes these works briefly. 1. The effect of the dielectric medium upon the spontaneous emission rate. The effect of the dielectric medium upon the spontaneous emission rate was investigated using lead borate glass of various compositions lightly doped with Eu3+. A dual approach used the variation of (i) electric dipole/magnetic dipole (ED/MD) emission rates from spectral integrations; and (ii) absolute ED emission rates from lifetime measurements for comparison with the variation of the refractive index of the glass medium. Contrary to a previous study Phys. Rev. Lett. 91, 203903(2003), the results show the relevance of the virtual cavity-model in this case. The MD emission rates were taken to follow the n3 increase in density of photon states in the medium. The justifications for employing Eu3+ for identifying the appropriate model are given. 2. Spectral properties of metal ion-doped glass A. Europium ion-doped lead borate glass. The emission spectra of the tripositive lanthanide ion Eu3+ have been employed to probe its environment in the solid state, and the intensity ratio of magnetic dipole (5D0 → 7F1) and forced electric dipole (5D0 → 7F2) transitions has been used to estimate the "degree of asymmetry" of a crystal site. From the site-selective, low temperature emission spectra of Eu3+ doped into a glass, a new empirical relation has been found between the width of spectral features and the relative intensity of the 5D0 → 7F0 zero phonon line. In order to explain the observations from experiments with excitation at different wavelengths, a generic quantitative relation has been developed from basic theory and validated from our experimental results. This work gives a deeper insight and understanding of the spectral characteristics of Eu3+ electronic spectra in the visible region. The relationship between the band width of luminescence spectral features and their relative intensities has also been investigated, using glasses doped with europium, Eu3+, over a wide composition range. Glasses of composition (B2O3)70(PbO)29(0.5Eu2O3)1 and (B2O3)z(PbO)99.6-z(0.5Eu2O3)0.4 (z = 20, 30, 40, 60, 70), were prepared by the melting-quenching technique. Variable-wavelength measurements by the prism-coupling method enabled interpolation of refractive index at selected wavelengths. Diffuse reflection spectra confirmed the incorporation of Eu3+ into the glass and scanning electron microscopy displayed that this was in a homogeneous manner. Vibrational spectra showed a change in boron coordination from BO3 to BO4 units with increase of B2O3 content in the glass. Multi-wavelength excited luminescence spectra were recorded for the glasses at temperatures down to 10 K and qualitative interpretations of spectral differences with change of B2O3 content are given. The quantitative analysis of 5D0 luminescence intensity-bandwidth relations showed that although samples with higher boron content closely exhibit a simple proportional relationship with band intensity ratios, as expected from theory, the expression needs to be slightly modified for those with low boron content. The Judd-Ofelt intensity analysis of the 5D0 emission spectra under laser excitations at low temperature gives Ω2 values within the range from (3.9-6.5) × 10-20 cm2, and Ω4 in the range from (4.1-7.0) × 10-20 cm2, for different values of z. However, no clear monotonic relation was found between the parameter values and composition. The Judd-Ofelt parameters are compared with those from other systems doped with Eu3+ and are found to lie in the normal ranges for Eu3+-doped glasses. The comparison of parameter values derived from the 10 K spectra with those from room temperature spectra for our glasses, which are fairly constant for different compositions, shows that site selection occurs at low temperature. B. Transition metal ion-doped sodium borosilicate glass and lead borate glass. The UV-Vis-NIR absorption and the luminescence properties of transition metal (3d (Ti → Zn), 4d (Nb, Mo, Ru and Rh), 5d (Ta, W, Re and Ir)) ion-doped sodium borosilicate glass were investigated, as well as transition metal (3d (V → Zn), the two 4d (Mo and Rh) and the three 5d (W, Re and Ir)) ion-doped lead borate glass. Transition metal ions produced intense broad absorption bands and moved the absorption edge of the doped glass to longer wavelength with increasing content of dopant ion in the glass. On the other hand, transition metal ions gave no, or weak, emission in the visible region, which may result from the high phonon energy of the host glass, the inability to populate luminescent states, or other quenching mechanisms. V, Cr, Mn, or Mo ion-doped glasses have been further investigated by the X-ray absorption near-edge structure (XANES) technique to study the valence states existing in the glass. Synchrotron radiation has been used to excite above the band gap of the host glass to study the higher energy levels of the corresponding transition metal ions, but the results do not indicate luminescence from the transition metal ions. 3. Energy transfer and luminescence studies between ions in glasses. A. Pr3+, Yb3+ pair in lead borate glass Lead borate glass samples doped with the tripositive lanthanide ions Pr3+ and Yb3+ were synthesized by the conventional melting-quenching method. The luminescence properties and energy transfer process from Pr3+ to Yb3+ were investigated. Upon ultraviolet excitation, the room temperature luminescence decay curve of a sample containing only a low concentration of Pr3+ exhibited monoexponential decay from 1D2 with the lifetime 37 μs, without emission from 3P0. The room temperature Pr3+ emission intensities decreased with the increase of Yb3+ mole ratio in the glass. Under the excitation of 454.5 nm at 10 K, a broad red emission band centered at 605 nm, and an NIR emission band at 995 nm were observed in the co-doped lead borate glass, originating from Pr3+ and Yb3+ ions, respectively. The decay curves of the 1D2 emission from Pr3+ with addition of Yb3+ in lead borate glass show non-monoexponential character, and are best described by a stretched exponential function. The average 1D2 decay time decreases considerably with the addition of Yb3+ in the glass. Decay curve fitting using a modified Inokuti-Hirayama expression indicates dipole-dipole energy transfer from Pr3+ to Yb3+, which is consistent with the expected cross-relaxation scheme. There is a good agreement of the estimated overall energy transfer efficiency obtained from the integrals under the normalized decay curves, or from the lifetimes fitted by the stretched exponential function, or from the average decay times. B. Pr3+, Yb3+ pair in sodium borosilicate glass Sodium borosilicate glass samples doped with the tripositive lanthanide ions Pr3+ and Yb3+ were synthesized by the conventional melting-quenching method. The luminescence properties and energy transfer process from Pr3+ to Yb3+ were investigated. Upon ultraviolet excitation, the room temperature luminescence decay curve of two samples containing only a low or relatively higher concentration of Pr3+ exhibited biexponential decay from 1D2 without emission from 3P0. The room temperature Pr3+ emission intensities decreased with the increase of Yb3+ mole ratio in the glass. Under the excitation of 454.5 nm at 10 K, a broad red emission band centered at 625 nm, and an NIR emission band at 995 nm were observed in the co-doped sodium borosilicate glass, originating from Pr3+ and Yb3+ ions, respectively. The decay curves of the 1D2 emission from Pr3+ with addition of Yb3+ in sodium borosilicate glass show non-monoexponential character, and are best described by a stretched exponential function. The average 1D2 decay time decreases considerably with the addition of Yb3+ in the glass. C. V5+, Eu3+ pair in sodium borosilicate glass Vanadium doped sodium borosilicate glasses were synthesized using V2O3 and V2O5 as the starting vanadium source, respectively. The absorption and luminescence properties of the V2O3 (or V2O5), Eu2O3 single or co-doped glass were investigated. The absorption intensity in the spectral region of 520-1500 nm increased with increase of V2O3 mole ratio in the glass; or by doping the same mole ratio of V2O3 instead of V2O5 in the glass; or by addition of Eu2O3 into the glass co-doped with V2O5. Addition of V2O3 gave the same absorption edge in the glass, as that for V2O5 at the same mole ratio, both shifting the edge to longer wavelength; while addition of Eu2O3 gave sharp characteristic absorption peaks of Eu3+ and had no effect on the absorption edge in the glass. Glass containing only a lower concentration of V2O5 gave the least absorption intensity in region of 520-1500 nm, and relatively strongest emission at ~526 nm, indicating the existence of V4+ playing a quenching role. The red emission from Eu3+ or broad emission centered at ~524 nm from V5+, when codoped Eu2O3 and V2O3 (or V2O5) in the glass, decreased in intensity to a large extent, indicating quenching of V5+ emission by V4+ and weak exchange energy transfer from V5+ to Eu3+ in the glass. Exceptionally, under excitation of 362 nm, glass containing both low concentrations of V2O3 and Eu2O3 produced broad emission centered at 526 nm and red emission with both almost unchanged intensity relative to the glass single doped lower concentration of V2O3 or Eu2O3. No further obvious energy transfer has been found between 5+V Eu3+ in the glass, still probably resulting from the existence of V4+ acting as a quencher and weak exchange interaction between V5+ and Eu3+ in the glass. Notes: CityU Call Number: QC464.G55 W46 2012; xxxi, 299 leaves : ill. (some col.) 30 cm.; Thesis (Ph.D.)--City University of Hong Kong, 2012.; Includes bibliographical references. 2012-01-01T00:00:00Z http://dspace.cityu.edu.hk:80/handle/2031/6896 Title: Design of semiconductor nanowires for high performance photocatalytic and electronic applications Authors: Wang, Fengyun (王鳳云) Abstract: Semiconductor nanowires (NWs), such as silicon (Si) and III-V materials, have recently stimulated a great interest in the scientific research community due to their unique electronic and optical properties. The III-V NWs are the fundamental elements in pursuing next-generation nanoelectronics; therefore, it is important to understand the growth mechanism for their large-scale and uniform NWs preparation, as well as to estimate their electronic transport properties for technological applications. In the meanwhile, Si NWs are the promising photocatalysts because of their large specific surface area, small band gaps and reactive Si-H surfaces formed by hydrofluoric acid (HF) treatment; therefore they would have prospective photocatalytic activity in the visible light range, as compared with the ultraviolet photocatalysts. In this regard, it is significant to investigate the physical properties of these NWs for the corresponding photocatalytic applications. In this dissertation, utilizing a solid source chemical vapor deposition (SSCVD) method, excellent carrier mobility indium phosphide (InP) NWs have been synthesized, by utilizing gold (Au) thin film catalyst, and the crystal structure and intrinsic electron transport properties are carefully studied. Notably, the NWs are found to grow via the vapor-liquid-solid (VLS) mechanism with a narrow distribution of diameter uniformly along the entire NW length. Although the grown NWs possess a substantial amount of twin defects, the fabricated NW field-effect transistors (FETs) still exhibit impressive electrical performance with high carrier mobility (~350 cm2/Vs) and ION/IOFF ratio (~106). All these have demonstrated the promising potential of such NWs grown on amorphous substrates for practical applications, as compared to the conventional metalorganic chemical vapor deposition (MOCVD) or molecular bean epitaxy (MBE) grown InP NWs. As Au is well known to be incompatible with the conventional Si-based complementary metal oxide semiconductor (CMOS) technology as the resultant deep level traps in Si greatly degrade the electrical properties, highly crystalline, stoichiometric and dense gallium arsenide (GaAs) NWs are synthesized on amorphous SiO2 substrates using Ni nano-clusters (NCs) as catalysts. The grown NWs have low defect densities and found to grow epitaxially via the vapor-solid-solid (VSS) mechanism with non-spherical NixGay catalytic seeds. The NWs are then configured into field-effect transistors (FETs) showing impressive electrical characteristics with ION/IOFF > 103. Using the same SSCVD method, diameter tailorable GaAs NWs have been prepared in the range of 10-200 nm. Importantly, there are abundant acceptor-like defect states located between the intrinsic nanowire and its amorphous native oxide shell, which can be used to alter electronic transport properties of GaAs nanowires as a function of diameter. Using a NW field-effect transistor (NWFET) device structure, p- to n-channel switching behaviors have been achieved with the increasing NW diameters as the thin NWs (< 40 nm) are fully depleted and the thick NWs (> 70 nm) are non-depleted and the medium diameter NWs (40-70 nm) are semi-depleted by the interface trapping effects. In this case, careful device design considerations are required for achieving the optimal NW device performances. The corresponding NW photovoltaic (PV) cells are then fabricated by using the Schottky contact of the NW with the Au-Ga catalyst tip, with the best performance of Voc ~0.6 V, Jsc ~11 mA/cm2, FF ~0.42 and efficiency ~2.8 % for a NW with diameter of 70 nm. As compared with metal contacts directly deposited on top of the nanowire, this nanoscale contact is found to allevia5te the well-known Fermi-level (EF) pinning to achieve effective formation of Schottky barrier responsible for the superior PV response. It should be noted that this simple structure resulted in comparable efficiency with the complex intentionally prepared p-n junction structured solar cells, showing the potential of these versatile nanoscale contact configurations for future technological device applications. Besides, large-scale uniform nanoporous and nonporous three-dimensional silicon nanowire arrays (SiNWAs) prepared with metal-assisted chemical etching method from different types of Si wafers were explored as photocatalysts for the dye photodegradation. The photocatalytic mechanism is that the dye molecules were decomposed by the ●OH radicals produced by the Si NWs after the absorption of photons with energy equal to or larger than its band gap. Importantly, after the hydrofluoric acid (HF) treatment, the photocatalytic activity of all kinds of SiNWAs increased significantly, which are caused by two reasons: some of the methyl red (MR) molecules can be reduced by hydrogen transfer firstly and then decomposed by ●OH radicals, which plays an important role in decomposing MR; Si NWs can produce ●OH radicals more easily by hydrogen terminated treatment. Besides, the nanoporous SiNWAs showed excellent stability, which can be recovered by HF treatment. The excellent photocatalytic activity and stability of porous Si nanowire arrays may have significant potential for organic waste treatment and environmental remediation. Notes: CityU Call Number: TK7874.85 .W36 2012; xx, 118 leaves : ill. (some col.) 30 cm.; Thesis (Ph.D.)--City University of Hong Kong, 2012.; Includes bibliographical references. 2012-01-01T00:00:00Z http://dspace.cityu.edu.hk:80/handle/2031/6895 Title: Chiral pyridine-containing ligands for supramolecular chemistry Authors: Tsang, Chui Shan (曾翠珊) Abstract: In the study, two types of chiral polydentate pyridine-containing ligands were prepared and reacted with different transition metal ions to afford different supramolecular complexes, and the chemistry of these complexes were explored. In chapter 2, with chiral 2,2′:6′,2:6″,2″:6″′,2″′′-quinquepyridine qqpy1, the diastereoselective synthesis of copper helicates of different nuclearity and valency was carried out. Two new copper helicates, a mixed-valence Cu(I,II) double-stranded helicate [Cu2(qqpy1)2](ClO4)3 (Cu-2) which was afforded from the reaction of qqpy1, Cu(MeCN)4(ClO4) and Cu(ClO4)2∙6H2O in a ratio of 2 to 1 to 1 and a tricopper (I) double-stranded helicate [Cu3(qqpy1)2](ClO4)3 (Cu-3) which was afforded from the reaction of Cu(MeCN)4(ClO4) and qqpy1 in a ratio of 3 to 2, were synthesized. All the complexes were successfully characterized by ESI-MS, elemental analysis and CD spectroscopy. The structures of Cu-2 and Cu-3 were successfully characterized by X-ray diffraction method and a short Cu···Cu distance was observed in the structure of Cu-3. Diastereoselective formation of Cu-3 was investigated using 1H NMR spectroscopy and the ratio of diastereomers was found to be 70:30 which was similar to the previously reported dicopper (I) double-stranded helicate [Cu2(qqpy1)2](ClO4)2 (Cu-1). The conversion of Cu-1 and Cu-3 was established by 1H NMR and CD spectroscopy, indicated that Cu-3 can be formed from Cu-1. For Cu-1 and Cu-2, reversible conversion can be achieved through a one electron transfer redox reaction which is demostrated previously using cyclic voltammetry. In addition, Cu-2 was synthesized from Cu-1 by reacting with Cu(ClO4)2∙6H2O. It was found that there is no change of helical chirality during reaction. Therefore, with this method, the ratio of diastereomers for the formation of Cu-2 was established to be 70:30, same as Cu-1. Because conversions between each helicate were demonstrated and similar ratios of diastereomers were observed, we propose that the formation of mixed-valence Cu-2 and trinuclear Cu-3 is through the formation of binuclear Cu-1. In chapter 3, with chiral tetradentate pyridylthiazole ligand pythz1 and two newly synthesized pyridylthiazole ligand pythz2 and pythz3, dinuclear Ag(I) double-stranded helicates were synthesized from the reaction of Ag(OAc)2∙2H2O and L (L = pythz1-3) in the ratio of 1 to 1. All the complexes were isolated as the PF6− salts and successfully characterized with elemental analysis, ESI-MS and CD spectroscopy. The crystal structures of helicates [Ag2(pythz2)2](PF6)2 and [Ag2(pythz3)2](PF6)2 were successfully characterized by X-ray diffraction method in which short Ag···Ag distance was found in both structures. The ratio of diastereomers of helicates were established using 1H NMR spectroscopy in which the diastereomeric ratio of [Ag2(pythz1)2](PF6)2 was 67:33 and [Ag2(pythz2)2](PF6)2 was greater than 95%. Because of the exchange of diastereomers in [Ag2(pythz3)2](PF6)2, the solution of the complex was freeze to 213 K and the diastereomeric ratio was found to be 83:17. To investigate whether the diastereoselectivity affects by the change of metal ion, the dicopper(I) double-stranded helicates [Cu2(pythz2)2](PF6)2 and [Cu2(pythz3)2](PF6)2 were synthesized and characterized with elemental analysis, ESI-MS and CD spectroscopy. Together with the previously reported dicopper(I) double-stranded helicate [Cu2(pythz1)2](PF6)2, the comparison between the Ag(I) and Cu(I) helicates found that the diastereoselectivity of [Ag2(pythz-1)2](PF6)2 and [Cu2(pythz-1)2](PF6)2 reversed in which the major diastereomer of [Ag2(pythz-1)2](PF6)2 was M-helicate while [Cu2(pythz-1)2](PF6)2 is P-helicate. To address the reverse in the diastereoselectivity upon the change of metal ions, firstly, the simulated structures of diastereomers of [Ag2(pythz1)2](PF6)2, P- and M-helicate were compared and the comparison showed the flattened structures of [Ag2(pythz1)2](PF6)2 diminished the close contact between the pinene C(CH3)2 group and the thiazole ring creating significant steric hindrance at the helical pitch of the P-helicate more than M-helicate, thus M-helicate was more preferred. Finally, the comparison between the simulated structures of M-[Ag2(pythz1)2](PF6)2 and P-[Cu2(pythz1)2](PF6)2 showed, in contrast to P-[Cu2(pythz1)2](PF6)2, the more flattened structure of M-[Ag2(pythz1)2](PF6)2 which was resulted from the short Ag···Ag distance allowing more space for the bulky pinene C(CH3)2 group to place at the head of helicate while the less bulky pinene CH2 group and the thiazole ring at the pitch of helicate did not increase the steric hindrance. As the steric hindrance occurred in P- [Cu2(pythz1)2](PF6)2 and M-[Ag2(pythz1)2](PF6)2 were at different position, opposite diastereoselectivity was observed. In chapter 4, with two new chiral tetradentate pyridyl-thiazole ligands pythz4 and pythz5, the effect of the difference in ligands’ directional angle on the formation of supramolecular structures was explored. Ligand pythz4 was considered as the position isomer of pythz5 because of their identical molecular structure but different in the bridging position of two bidentate pyridyl-thiazole binding units. The complexation of pythz4 and pythz5 with octahedral metal ions resulted in different supramolecular complexes under identical reaction condition, a dinuclear triple-stranded helicate [M2(pythz4)3](ClO4)4 and a tetrahedral cage [M4(pythz5)6](ClO4)8 respectively. All the complexes were successfully characterized with elemental analysis and ESI-MS. Triplestranded helical structure of [Cu2(pythz4)3](ClO4)4 was successfully characterized by Xray diffraction method while no tetrahedral cage structure with pythz5 was characterized. However, cage structures of a similar ligand [Ni4(pythz6)6](ClO4)8 and [Cd4(pythz6)6](ClO4)8 were successfully characterized. The difference in the formation of supramolecular complexes using similar pyridyl-thiazole ligands was explained by the difference in the directional angle of the ligand strands. In the case of M = Mn, complexes of all three ligands (pythz4-6) were active catalysts in the epoxidation of styrene, and [Mn4(pythz5)6](ClO4)8 showed the best result in which the conversion of styrene was 89% with 73% yield of styrene oxide in 3 h. Notes: CityU Call Number: QD262 .T74 2012; xi, 196 leaves : ill. (some col.) 30 cm.; Thesis (Ph.D.)--City University of Hong Kong, 2012.; Includes bibliographical references (leaves 184-196) 2012-01-01T00:00:00Z http://dspace.cityu.edu.hk:80/handle/2031/6894 Title: Thermal and photochemical water oxidation catalysed by polypyridyl complexes of ruthenium, cobalt, nickel, and iron Authors: Ng, Siu Mui (吳少梅) Abstract: The search for efficient and cost-effective methods for solar-driven splitting of water is one of the most challenging tasks facing scientists in this century. Considerable efforts have been made by chemists in recent years to develop efficient transition metal catalysts for water oxidation. Water oxidation provides a scalable source of electrons and protons for the production of fuels such as in the reduction of protons to hydrogen and that of carbon dioxide to methanol. In order to be economically practical, catalysts should be made from earth-abundant materials. So far, however, only a few cobalt, manganese and iron water oxidation catalysts (WOCs) have been developed. In this thesis, a number of transition metal complexes with polypyridyl ligands designed for catalytic water oxidation are reported. Three polypyridyl ligands 2,2':6',2'':6'',2''':6''',2'''':6'''',2'''''-sexipyridine (sexipy), 2,2':6',2'':6'',2'''-quaterpyridine (qpy) and 2-hydroxy-1,10-phenanthroline (PhenOH) have been synthesised and characterised by IR and 1H NMR spectroscopy as well as CHN elemental analysis. Dinuclear ruthenium complexes [Ru2(μ-sexipy)(bpy)2(H2O)2](ClO4)4 (bpy = 2,2’-bipyridine) and [Ru2(μ-sexipy)(clbpy)2(H2O)2](ClO4)4 (clbpy = 4,4’-dichloro-2,2’-bipyridine) have been synthesised and characterised. These compounds catalysed chemical water oxidation using Ce(IV) as the oxidant with a turnover number (TON) of 220. They also catalysed visible light-driven water oxidation using [Ru(bpy)3]2+ as the photosensitiser and Na2S2O8 as the sacrificial oxidant. Three cobalt complexes trans-[Co(qpy)(H2O)2](ClO4)2, cis-[Co(bpy)2(H2O)2](ClO4)2 and cis-[Co(PhenO)2(H2O)2](NO3), a nickel complex cis-[Ni(PhenOH)2Cl2] and an iron complex [(μ3-O)Fe3(μ-OMe)(μ-PhenO)4(Cl)]Cl have been synthesised and characterised by IR spectroscopy, electrospray ionisation mass spectrometry (ESI-MS), 1H NMR spectroscopy, CHN elemental analysis and UV-Vis spectroscopy. Their structures have also been determined by X-ray crystallography. These complexes catalysed water oxidation at pH 8-9 using [Ru(bpy)3]3+ as the chemical oxidant. They also catalysed photochemical oxidation of water using [Ru(bpy)3]2+ as the photosensitiser and Na2S2O8 as the sacrificial oxidant. In addition, a series of ruthenium isocyanide complexes containing 8-quinolinolato ligands with formula [RuQ2(RNC)2] (Q = 8-quinolinolate, R = tert-butyl; 6.1, 4-methoxyphenyl (4-MeOPh); 6.2, 4-chlorophenyl (4-ClPh); 6.3, 2,4,6-tribromophenyl (2,4,6-Br3Ph); 6.4) and trans,trans,trans-[Ru(Tol-Q)2(tBuNC)2] (Tol-Q = 8-hydroxyl-5-tolylquinolinate, 6.6) have been prepared and characterised by IR spectroscopy, ESI-MS, 1H NMR spectroscopy, CHN elemental analysis and UV-Vis spectroscopy. These complexes exhibited intense absorption in the UV region (λmax = 320-390 nm) with molar extinction coefficients (ε) on the order of 104 dm3 mol-1 cm-1 and moderately intense absorption with ε on the order of 103 dm3 mol-1 cm-1 at 400-492 nm. The intense absorption at 320-390 nm has been assigned to the ligand-centred π → π* transitions of the quinolinolate ligands, probably mixed with the π → π* transitions of the isocyanide ligands. The lower-energy absorption at 400-492 nm have been assigned to metal-to-ligand charge-transfer (MLCT) transitions. Upon excitation at λ > 350 nm, complexes 6.1a-6.3a displayed orange-red luminescene in dichloromethane at 298 K. In EtOH/MeOH glass, complexes 6.1-6.4 and 6 showed intense structured emission (593-638 nm). Notes: CityU Call Number: TD468 .N45 2012; xxviii, 202 leaves : ill. 30 cm.; Thesis (Ph.D.)--City University of Hong Kong, 2012.; Includes bibliographical references (leaves 189-202) 2012-01-01T00:00:00Z