Browsing by Author "Luo, Liyang"

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An Investigation on the Luminescence and Ce(3+) -> Eu(2+) Energy Transfer in Ca(9)Y(PO(4))(7):Ce(3+),Eu(2+) Phosphor
(2011-01-01)
Huang, Chien-Hao
;
Luo, Liyang
;
Chen, Teng-Ming
;
應用化學系
;
Department of Applied Chemistry
A series of Ce(3+)- and Eu(2+)-coactivated Ca(9)Y(PO(4))(7) phosphors were synthesized by high temperature solid-state reactions. The Ca(9)Y(PO(4))(7):Ce(3+), Eu(2+) phosphor showed two emission bands under 292 nm excitation:the one observed at 342 nm was attributed to the 4f(0)5d(1) -> 4f(1) transition of Ce(3+) ion emission, and the other found at 492 nm was assigned to the 4 f(6)5d(1) -> 4f(7) transition of Eu(2+) ions. Through an effective resonance-type energy transfer, the Ca(9)Y(PO(4))(7):Ce(3+), Eu(2+) phosphors exhibit a systematically varied hues from ultraviolet to blue-greenish and the relative intensity of ultraviolet and blue-greenish emissions can be tuned by properly tuning the relative dopant composition of Ce(3+)/Eu(2+). The energy transfer from a sensitizer Ce(3+) to an activator Eu(2+) in Ca(9)Y(PO(4))(7) host matrix was studied and demonstrated to be a resonant type via a dipole-dipole mechanism based on the decay lifetime analysis. Furthermore, we have calculated the critical distance for Ce(3+) -> Eu(2+) energy transfer to be about 30.7 angstrom by both concentration quenching and spectral overlap methods. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.029111jes] All rights reserved.
An Investigation on the Luminescence and Ce3+ -> Eu2+ Energy Transfer in Ca9Y(PO4)(7):Ce3+,Eu2+ Phosphor
(2011-01-01)
Huang, Chien-Hao
;
Luo, Liyang
;
Chen, Teng-Ming
;
應用化學系
;
Department of Applied Chemistry
A series of Ce3+- and Eu2+-coactivated Ca9Y(PO4)(7) phosphors were synthesized by high temperature solid-state reactions. The Ca9Y(PO4)(7):Ce3+, Eu2+ phosphor showed two emission bands under 292 nm excitation:the one observed at 342 nm was attributed to the 4f(0)5d(1) -> 4f(1) transition of Ce3+ ion emission, and the other found at 492 nm was assigned to the 4 f(6)5d(1) -> 4f(7) transition of Eu2+ ions. Through an effective resonance-type energy transfer, the Ca9Y(PO4)(7):Ce3+, Eu2+ phosphors exhibit a systematically varied hues from ultraviolet to blue-greenish and the relative intensity of ultraviolet and blue-greenish emissions can be tuned by properly tuning the relative dopant composition of Ce3+/Eu2+. The energy transfer from a sensitizer Ce3+ to an activator Eu2+ in Ca9Y(PO4)(7) host matrix was studied and demonstrated to be a resonant type via a dipole-dipole mechanism based on the decay lifetime analysis. Furthermore, we have calculated the critical distance for Ce3+ -> Eu2+ energy transfer to be about 30.7 angstrom by both concentration quenching and spectral overlap methods. (C) 2011 The Electrochemical Society. [DOI: 10.1149/2.029111jes] All rights reserved.
Design and Characterization of Novel Porphyrins with Oligo(phenylethylnyl) Links of Varied Length for Dye-Sensitized Solar Cells: Synthesis and Optical, Electrochemical, and Photovoltaic Investigation
(2009-01-15)
Lin, Ching-Yao
;
Lo, Chen-Fu
;
Luo, Liyang
;
Lu, Hsueh-Pei
;
Hung, Chen-Shiung
Novel zinc porphyrins with 1-4 pi-conjugated phenylethyinyl (PE) units (labeled PE1-PE4) as a link of controlled length were synthesized for fundamental tests and applications as a dye-serisitized solar cell (DSSC). The UV-visible spectra of the solution samples show clear absorption patterns of the PE groups in a region 300-400 nm, consistent with results calculated with density-functional theory. Cyclic voltammograms of PE1-PE4 in tetrahydrofuran show similar electrochemical potentials for each compound. Ferntosecond fluorescence up-conversion of solution samples and of porphyrin-sensitized TiO(2) films was measured with excitation at 420 or 430 nm and emission at 460, 470, 620, and 680 nm. When these porphyrins were fabricated into DSSC devices, the efficiency of power conversion of these devices decreased systematically with increasing length of the link: 2.5 +/- 0.2% (PE1), 2.0 +/- 0.1% (PE2), 0.78 +/- 0.09% (PE3), 0.25 +/- 0.02% (PE4). This great photovoltaic degradation from PE1 to PE4 is not interpretable according to the rate of electron injection independent of length; other factors, including electron transfer from the semiconductor back to the porphyrin cation or the electrolyte, must be considered to account for the observed dependence of photovoltaic performance on length.
Different sensing modes of fluoride and acetate based on a calix[4]arene with 25,27-bistriazolylmethylpyrenylacetamides
(2014)
Hung, Hao-Chih
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Chang, Yung-Yu
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Luo, Liyang
;
Hung, Chen-Hsiung
;
Diau, Eric Wei-Guang
25,27-Bis{1'-N-(1-pyrenyl)-aminocarbonylmethyl-1H-[1',2',3']tri-azolyl-4'-methoxy}-26,28-dihydroxycalix-[4]arene, 4, is synthesized as a fluorescent chemosensor for the selective detection of both anions and ion pairs in MeCN. Sensor 4 uses bis-triazoles as ligands to bind a metal ion, bis-amides and bis-triazoles as the sites to recognize anions, and pyrenes as fluorophores. Among eight anions screened, chemosensor 4 showed a marked fluorescence change toward F-, H2PO4- and AcO-, but 4 responded to each anion in a distinct way. In the presence of F- at low concentrations, the dynamic excimer emission of compound 4 at lambda(max) 482 nm was quenched, but an emission at lambda(max) 472 nm appeared at large doses of F-. A control compound 6 showed very similar red shifts in the UV-vis and excitation spectra as 4 did, and its 472 nm emission band grew as the fluoride doses increased. Thus, the growth of the 472 nm emission of 4 and 6 in the presence of excess F- may be because strong H-bonding interactions of amido protons with F- favoured the formation of pyrene dimers in the ground state with charge transfer characteristics. The addition of H2PO4-, unlike F-, to a solution of 4 showed an enhanced monomer emission but a decreased excimer emission (lambda(max) 482 nm). Adding AcO- to 4 produced a systematic change from a dynamic excimer (lambda(max) 482 nm) to lambda(max) 472 nm but with very little change in the UV-vis spectrum. Time-resolved fluorescence measurements on compound 6 with F- and AcO- confirmed that the 472 nm emission band mainly came from static excimers for the former, but was partly from a dynamic excimer for the latter because it contained a growth component in the fluorescence decay traces. Without pre-treatment with an anion, chemosensor 4 showed recognition of only metal ions Cu2+, Hg2+ and Cr3+, but it became sensitive to Ag+ when it was pretreated with fluoride.
Effects of aggregation and electron injection on photovoltaic performance of porphyrin-based solar cells with oligo(phenylethynyl) links inside TiO(2) and Al(2)O(3) nanotube arrays
(2010-01-01)
Luo, Liyang
;
Lin, Chia-Jung
;
Tsai, Chiau-Yiag
;
Wu, Hui-Ping
;
Li, Lu-Lin
Porphyrins with phenylethynyl links of varied length (PE1-PE4) were sensitized on vertically oriented, anodic titanium-oxide (ATO) nanotube arrays for application as dye-sensitized solar cells (DSSC). The efficiency of power conversion decreased systematically from the dye with a short link to the dye with a long link. We measured the efficiency of conversion of incident photons to current (IPCE), the photocurrent decay of the devices, and steady-state and time-resolved fluorescence spectra of the thin-film samples to understand how the cell performance depends on the length of the link. Measurements of femtosecond fluorescence confirmed that the efficiency of electron injection depended on length because of dye aggregation that significantly increased the rate of aggregate-induced energy transfer for porphyrins with a long link. The rate of electron injection depended on the length of the link with an attenuation factor beta similar to 0.1 angstrom(-1). Resonant energy transfer (RET) kinetics of porphyrins sensitized on anodic aluminium-oxide (AAO) nanotube arrays were performed with picosecond time-correlated single-photon counting and four molecular densities for each porphyrin. The kinetic data of PE1 and PE2 are described satisfactorily according to a Forster model, whereas those of PE3 and PE4 conform to a Dexter formula. A formation of clusters is proposed to rationalize the observed density-dependent kinetics for the RET of porphyrins on semiconductor films.
Effects of aggregation and electron injection on photovoltaic performance of porphyrin-based solar cells with oligo(phenylethynyl) links inside TiO2 and Al2O3 nanotube arrays
(2010-01-01)
Luo, Liyang
;
Lin, Chia-Jung
;
Tsai, Chiau-Yiag
;
Wu, Hui-Ping
;
Li, Lu-Lin
Porphyrins with phenylethynyl links of varied length (PE1-PE4) were sensitized on vertically oriented, anodic titanium-oxide (ATO) nanotube arrays for application as dye-sensitized solar cells (DSSC). The efficiency of power conversion decreased systematically from the dye with a short link to the dye with a long link. We measured the efficiency of conversion of incident photons to current (IPCE), the photocurrent decay of the devices, and steady-state and time-resolved fluorescence spectra of the thin-film samples to understand how the cell performance depends on the length of the link. Measurements of femtosecond fluorescence confirmed that the efficiency of electron injection depended on length because of dye aggregation that significantly increased the rate of aggregate-induced energy transfer for porphyrins with a long link. The rate of electron injection depended on the length of the link with an attenuation factor beta similar to 0.1 angstrom(-1). Resonant energy transfer (RET) kinetics of porphyrins sensitized on anodic aluminium-oxide (AAO) nanotube arrays were performed with picosecond time-correlated single-photon counting and four molecular densities for each porphyrin. The kinetic data of PE1 and PE2 are described satisfactorily according to a Forster model, whereas those of PE3 and PE4 conform to a Dexter formula. A formation of clusters is proposed to rationalize the observed density-dependent kinetics for the RET of porphyrins on semiconductor films.
Effects of Core-modification on Porphyrin Sensitizers to the Efficiencies of Dye-sensitized Solar Cells
(2014-05-01)
Mane, Sandeep B.
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Luo, Liyang
;
Chang, Gao-Fong
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Diau, Eric Wei-Guang
;
Hung, Chen-Hsiung
To study dye-sensitized solar cells (DSSCs) with core-modified porphyrins as the sensitizing dyes, three porphyrins with an ethynyl benzoic acid as an anchoring group are prepared. The properties of free-base regular porphyrin (N4), thiaporphyrin (N3S) and oxaporphyrin (N3O) were thoroughly studied by spectroscopic methods, DFT calculations, and photovoltaic measurements. Replacing one of the porphyrinic core nitrogen atoms by oxygen or sulfur considerably changes the absorption spectra. The Soret band of the N3O and N3S observed bathochromic shifts of 3-9 nm while the Q band reaches 700 nm to the near-infrared region. The overall conversion efficiencies of the DSSCs based on these porphyrins are in the order N4 (3.66%) >> N3S (0.22%) > N3O (0.01%). The time-correlated single photon counting observed short fluorescence lifetimes for N3O adsorbed both on TiO2 and Al2O3 which explicates the poor efficiency of DSSC using N3O as the photosensitizer.
Effects of Porphyrinic meso-Substituents on the Photovoltaic Performance of Dye-Sensitized Solar Cells: Number and Position of p-Carboxyphenyl and Thienyl Groups on Zinc Porphyrins
(2012-06-07)
Ambre, Ram
;
Chen, Kwan-Bo
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Yao, Ching-Fa
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Luo, Liyang
;
Diau, Eric Wei-Guang
In order to understand the effects of meso-substituents of the zinc porphyrins on optical, electrochemical, and photovoltaic properties, a series of porphyrins with different combinations of thienyl (S) and p-carboxyphenyl (A) groups as the meso substituents have been systematically synthesized and studied. The properties of zinc complexes 3S1A, trans-2S2A, cis-2S2A, and 1S3A were fully investigated by absorption and emission spectra, attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectra, density functional theory (DFT) calculations, electrochemical, photophysical, and photovoltaic measurements. With the increasing number of meso-thienyl groups, slight red-shifts of Soret and Q bands were observed in both absorption and emission spectra. All of the absorption spectra of zinc porphyrins on TiO2 film show broadening and splitting of Soret bands because of excitonic coupling of porphyrins. ATR-FTIR spectra revealed likely modes to determine either a single arm (in 3S1A and trans-2S2A) or double arms (in 1S3A and cis-2S2A) attached on TiO2. Two factors of p-carboxyphenyl and thienyl groups affecting the devices performance-heavy atom effect and the amount of dye loading on TiO2-are concluded. Overall, the power conversion efficiencies (eta) of the devices exhibit the following order: 1S3A (3.0%) > cis-2S2A (2.5%) > trans-2S2A (1.8%) >> 3S1A (0.2%).
Effects of potential shift and efficiency of charge collection on nanotube-based porphyrin-sensitized solar cells with conjugated links of varied length
(2010)
Luo, Liyang
;
Lin, Chia-Jung
;
Hung, Chen-Shiung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
For dye-sensitized solar-cell devices fabricated from porphyrin sensitizers with links of varied length (PE1-PE4) adsorbed on anodic titanium-oxide nanotube arrays, we measured induced photocurrent and photovoltage decays under constant bias illumination; the evaluated efficiencies of charge collection of the devices show a systematic trend PE4 > PE3 > PE2 > PE1 at a large short-circuit current, implying that a long link would improve the charge separation if the electrons were effectively injected into the semiconductor.
Fabrication and Characterization of Anodic Titanium Oxide Nanotube Arrays of Controlled Length for Highly Efficient Dye-Sensitized Solar Cells
(2008-12-04)
Chen, Chien-Chon
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Chung, Hsien-Wen
;
Chen, Chin-Hsing
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Lu, Hsuch-Pei
;
Lan, Chi-Ming
The performance of dye-sensitized solar cells (DSSC), made of highly ordered anodic titanium oxide (ATO) nanotube (NT) arrays produced directly on Ti foil, depends on the length of these arrays. We controlled these lengths L from 4 to 41 mu m while varying the concentration (0.1, 0.25, 0.5, and 0.8 wt %) of the electrolyte (NH(4)F) in ethylene glycol in the presence of H(2)O (2 vol %) with anodization for various periods (t = 0.5-8 h). The compact and bundle layers introduced. during anodization were effectively removed upon simple ultrasonic cleaning in deionized water containing submicrometer particles of Al(2)O(3) in a small proportion. The photovoltaic performance of the NT-DSSC devices (NH4F at 0.5 wt %) made of ATO films, as prepared, increased from 3.0% to 5.2% as L was increased from 6 mu m (t = 0.5 h) to 30 mu m (t = 8 h). After treatment of the ATO films with TiCl(4) in a two-step annealing process, the optimized NT-DSSC device attained an overall efficiency of 7.0% power conversion.
Femtosecond Transient Absorption of Zinc Porphyrins with Oligo(phenylethylnyl) Linkers in Solution and on TiO(2) Films
(2009-07-09)
Chang, Chih-Wei
;
Luo, Liyang
;
Chou, Chung-Kung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
We measured femtosecond transient absorption of dye solutions and TiO(2) films sensitized with two zinc porphyrins (PE1 and PE4) to investigate the interfacial dynamics of electron transfer in relation to the dependence of cell performance on the length of the linker (Lin, C.-Y.; Lo, C.-F.; Luo, L.; Lu, H.-P.; Hung, C.-S.; Diau, E. W.-G. J. Phys. Chem. C 2009, 113, 755-764). For both porphyrins adsorbed on TiO(2) films with S(1) excitation (lambda(ex) = 620 nm), the transient absorption kinetics probed at 630 nm and 4.9 mu m are complementary to each other because only the excited-state and ground-state species were observed at 630 nm whereas only the charge-separation intermediates were observed at 4.9 mu m. The transient of the PE1/TiO(2) film shows a single exponential decay with a large offset, whereas the transient of the PE4/TiO(2) film displays a biexponential decay with a small offset. Because of the existence of an additional ps component, the amount of free delocalized electrons (offset signal) in PE4/TiO(2) is smaller than that in PEI/TiO(2). Our results imply that back electron transfer at the TiO(2)/dye interface is an important factor to be considered to account for the cell performance of a device.
Femtosecond Transient Absorption of Zinc Porphyrins with Oligo(phenylethylnyl) Linkers in Solution and on TiO2 Films
(2009-07-09)
Chang, Chih-Wei
;
Luo, Liyang
;
Chou, Chung-Kung
;
Lo, Chen-Fu
;
Lin, Ching-Yao
We measured femtosecond transient absorption of dye solutions and TiO2 films sensitized with two zinc porphyrins (PE1 and PE4) to investigate the interfacial dynamics of electron transfer in relation to the dependence of cell performance on the length of the linker (Lin, C.-Y.; Lo, C.-F.; Luo, L.; Lu, H.-P.; Hung, C.-S.; Diau, E. W.-G. J. Phys. Chem. C 2009, 113, 755-764). For both porphyrins adsorbed on TiO2 films with S-1 excitation (lambda(ex) = 620 nm), the transient absorption kinetics probed at 630 nm and 4.9 mu m are complementary to each other because only the excited-state and ground-state species were observed at 630 nm whereas only the charge-separation intermediates were observed at 4.9 mu m. The transient of the PE1/TiO2 film shows a single exponential decay with a large offset, whereas the transient of the PE4/TiO2 film displays a biexponential decay with a small offset. Because of the existence of an additional ps component, the amount of free delocalized electrons (offset signal) in PE4/TiO2 is smaller than that in PEI/TiO2. Our results imply that back electron transfer at the TiO2/dye interface is an important factor to be considered to account for the cell performance of a device.
Ferntosecond fluorescence dynamics of zinc biphenylporphine in nanocrystalline TiO2 films: Evidence for interfacial electron transfer through space
(2006-12-11)
Luo, Liyang
;
Chang, Chih-Wei
;
Lin, Ching-Yao
;
Diau, Eric Wei-Guang
;
應用化學系
The femtosecond fluorescence dynamics of zinc biphenylporphine (ZnBPP) were investigated in solution and in two solid-state environments - ZnBPP/glass and ZnBPP/TiO2 - with S-2 excitation (lambda(ex) = 410 nm and lambda(em) = 630 nm). Our results indicate that the transient in solution involves a persistent component that becomes completely quenched in thin-film samples; for solid films at least three decay coefficients are required to fit the transients. For ZnBPP/TiO2 films, the fluorescence was quenched significantly through J-type aggregation and interfacial electron transfer (IET) through space. Photocurrent measurements were also performed to confirm the existence of IET through space between ZnBPP molecules and TiO2 nanoparticles. (c) 2006 Elsevier B.V. All rights reserved.
Functional gold nanoclusters as antimicrobial agents, for antibiotic-resistant bacteria
(2010-07-01)
Chen, Wei-Yu
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Lin, Ju-Yu
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Chen, Wei-Jen
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Luo, Liyang
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Diau, Eirc Wei-Guang
Aims: Our aim was to demonstrate that lysozyme-directed generation of gold nanoclusters (Au NCs) are potential antimicrobial agents for antibiotic-resistant bacteria and broad labeling agents for pathogenic bacteria. Materials & methods: Lysozyme is an enzyme that is capable of hydrolyzing the cell walls of bacteria. In this study, we demonstrated the generation of functional Au NCs by using lysozyme as the sequester and the reducing agent for Au precursors at 40 degrees C. In addition, to shorten the reaction time, the reaction was conducted under microwave irradiation within a short period of time for the first time. Results: The bioactivity of the lysozyme on the Au NCs was retained. Therefore, the as-prepared lysozyme Au NCs with desirable fluorescence feature were successfully employed to be broad-band labeling agents for pathogenic bacteria. Furthermore, we also demonstrated that the lysozyme Au NCs can be used to effectively inhibit the cell growth of notorious antibiotic-resistant bacteria, including pan-drug-resistant Acinetobacter baumannii and vancomycin-resistant Enterococcus faecalis. Conclusion: The potential of employing the lysozyme Au NCs for bacterial labeling and as antimicrobial agents is expected.
Novel expanded porphyrin sensitized solar cells using boryl oxasmaragdyrin as the sensitizer
(2013)
Mane, Sandeep B.
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Hu, Jyun-Yu
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Chang, Yu-Cheng
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Luo, Liyang
;
Diau, Eric Wei-Guang
Oxasmaragdyrin boron complexes were prepared and applied in DSSCs. The HOMO-LUMO energy gap analyses and theoretical calculations revealed that these expanded porphyrins are ideal sensitizers for DSSCs. A device containing oxasmaragdyrin-BF2 as the sensitizer achieves an energy conversion efficiency of 5.7%.
Novel Steroid-Sensing Model and Characterization of Protein Interactions Based on Fluorescence Anisotropy Decay
(2010-04-01)
Chang, Ko-Shing
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Luo, Liyang
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Chang, Chih-Wei
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Huang, Yen-Chieh
;
Cheng, Chih-Yu
Intramolecular binding of a ligand with an alkyl link, (-CH(2))(3), covalently bound to a residue near the active site of the protein forms a novel steroid-sensing model. A genetically engineered Delta(5)-3-ketosteroid isomerase (KSI) was designed to conjugate uniquely with this ligand at its Cys-86 through the formation of a disulfide bond. The steady-state protein-ligand binding, mediated by hydrophobic interactions, was confirmed with fluorescence spectra, and the fluorophore-labeled peptide sequence was identified with tandem mass spectra. A comparison of steady-state fluorescence spectra of various fluorophore-labeled KS1 mutants reveals that the emission characteristics vary with environmental factors. An evaluation of the decay of the fluorescence anisotropy of the fluorophore indicates the existence of an intramolecular protein-ligand binding interaction. The measurement of time-resolved fluorescence anisotropy of various protein-ligand complexes yielded values of anisotropy decay representing the degrees of freedom of the fluorophore related to its location, inside or Outside the steroid-binding domain. When 19-norandrostenedione (19-NA) was added to this protein-ligand system, competitive binding between the ligand and the steroid was observed; this finding confirms the feasibility of the design of steroid detection with engineered KSI. On integration of this protein-ligand system with a silicon-based nanodevice (a p-type field-effect transistor with an Ultrathin body), it noncharged steroid, 19-NA, became detectable at it micromolar level (Biosens. Bioelectron. 2008, 23, 1883).
Photoactivation Studies of Zinc Porphyrin-Myoglobin System and Its Application for Light-Chemical Energy Conversion
(2011)
Chang, Chin-Hao
;
Hu, Yi-Ting
;
Lo, Chen-Fu
;
Luo, Liyang
;
Lin, Hung-Ming
An artificial zinc porphyrin-myoglobin- based photo-chemical energy conversion system, consisting of ZnPP-Mb or ZnPE1-Mb as a photosensitizer, NADP(+) as an electron acceptor, and triethanolamine as an electron donor, has been constructed to mimic photosystem I. The photoirradiated product is able to reduce a single-electron acceptor protein cytochrome c, but cannot catalyze the two-electron reduction of acetaldehyde by alcohol dehydrogenase, thus demonstrating a single electron transfer mechanism. Furthermore, the artificial system can bifunctionally promote oxidoredox reactions, depending on the presence or absence of a sacrificial electron donor, thus suggesting its potential application in electrochemical regeneration steps involved in chemical transformation and/or energy conversion.
The cis-isomer performs better than the trans-isomer in porphyrin-sensitized solar cells: interfacial electron transport and charge recombination investigations
(2015-01-01)
Luo, Liyang
;
Ambre, Ram B.
;
Mane, Sandeep B.
;
Diau, Eric Wei-Guang
;
Hung, Chen-Hsiung
We report characterizations and device performance for dye-sensitized solar cells using cis- and trans-isomers of 2D-pi-2A zinc porphyrins with carboxyphenyl and thienyl groups in their meso-positions. Under identical experimental conditions with similar dye loadings, we observed overall power conversion efficiencies of 2.44% and 0.88% for devices made of cis-2S2A and trans-2S2A, respectively. This uneven performance among cis and trans isomers under the same experimental conditions can be rationalized with detailed investigations via spectroscopic, quantum chemical, and femtosecond fluorescence up-conversion investigations. Density functional theory (DFT) calculations show that a small amount of electron density is localized over carboxyphenyl groups in the LUMO of cis-2S2A, but there is no electron density populated on the carboxyphenyl groups in the LUMO of trans-2S2A. The femtosecond fluorescence decay measurements revealed that the excited-state lifetime of trans-2S2A on Al2O3 is half of that of cis-2S2A on Al2O3. Moreover, the dye-to-TiO2 electron injection time of trans-2S2A is 2.54 ps, which is shorter than that of cis-2S2A/TiO2 (2.95 ps). Electrochemical impedance spectra measured under one sun illumination also revealed that the charge recombination time of cis-2S2A is longer than that of trans-2S2A. This thorough understanding of isomeric effects on the performance of porphyrins will serve as a guideline for the design of future sensitizing dyes for solar cells.
Ultrafast relaxation of zinc protoporphyrin encapsulated within apomyoglobin in buffer solutions
(2007-07-05)
Luo, Liyang
;
Chang, Chin-Hao
;
Chen, Yue-Ching
;
Wu, Tung-Kung
;
Diau, Eric Wei-Guang
The relaxation dynamics of a zinc protoporphyrin (ZnPP) in THF, KPi buffer, and encapsulated within apomyoglobin (apoMb) was investigated in its excited state using femtosecond fluorescence up-conversion spectroscopy with S-2 excitation (lambda(ex) = 430 nm). The S-2 -> S-1 internal conversion of ZnPP is ultrafast (tau < 100 fs), and the hot S-1 ZnPP species are produced promptly after excitation. The relaxation dynamics of ZnPP in THF solution showed a dominant offset component (tau = 2.0 ns), but it disappeared completely when ZnPP formed aggregates in KPi buffer solution. When ZnPP was reconstituted into the heme pocket of apoMb to form a complex in KPi buffer solution, the fluorescence transients exhibited a biphasic decay feature with the signal approaching an asymptotic offset: at lambda(em) = 600 nm, the rapid component decayed in 710 fs and the slow one in 27 ps; at lambda(em) = 680 nm, the two time constants were 950 fs and 40 ps. We conclude that (1) the fast-decay component pertains to an efficient transfer of energy from the hot S-1 ZnPP species to apoMb through a dative bond between zinc and proximal histidine of the protein; (2) the slow-decay component arises from the water-induced vibrational relaxation of the hot S-1 ZnPP species; and (3) the offset component is due to S-1 -> T-1 intersystem crossing of the surviving cold S-1 ZnPP species. The transfer of energy through bonds might lead the dative bond to break, which explains our observation of the degradation of ZnPP-Mb samples in UV-vis and CD spectra upon protracted excitation.
Using Gold Nanoclusters As Selective Luminescent Probes for Phosphate-Containing Metabolites
(2012-07-03)
Li, Po-Han
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Lin, Ju-Yu
;
Chen, Cheng-Tai
;
Ciou, Wei-Ru
;
Chan, Po-Han
Glutathione-bound gold nanoclusters (AuNCs@GSH) can emit reddish photoluminescence under illumination of ultraviolet light. The luminescence of the AuNCs@GSH is quenched when chelating with iron ions (AuNCs@GSH-Fe3+), presumably resulting from the effective electron transfer between the nanoclusters and iron ions. Nevertheless, we found that the luminescence of the gold nanoclusters can be restored in the presence of phosphate-containing molecules, which suggested the possibility of using AuNCs@GSH-Fe3+ complexes as the selective luminescent switches for phosphate-containing metabolites. Phosphate-containing metabolites such as adenosine-5'-triphosphate (ATP) and pyrophosphate play an important role in biological systems. In this study, we demonstrated that the luminescence of the AuNCs@GSH-Fe3+ is switched-on when mixing with ATP and pyrophosphate, which can readily be observed by the naked eye. It results from the high formation constants between phosphates and iron ions. When employing fluorescence spectroscopy as the detection tool, quantitative analysis for phosphate-containing metabolites such as ATP and pyrophosphate can be conducted. The linear range for ATP and pyrophosphate is 50 mu M to sub-millimolar, while the limit of detection for ATP and pyrophosphate are similar to 43 and similar to 28 mu M, respectively. Additionally, we demonstrated that the luminescence of the AuNCs@GSH-Fe3+ can also be turned on in the presence of phosphate-containing metabolites from cell lysates and blood plasma.