Browsing by Author "Hsu, Hung-Yu"

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A strategy to design highly efficient porphyrin sensitizers for dye-sensitized solar cells
(2011)
Chang, Yu-Cheng
;
Wang, Chin-Li
;
Pan, Tsung-Yu
;
Hong, Shang-Hao
;
Lan, Chi-Ming
We designed highly efficient porphyrin sensitizers with two phenyl groups at meso-positions of the macrocycle bearing two ortho-substituted long alkoxyl chains for dye-sensitized solar cells; the ortho-substituted devices exhibit significantly enhanced photovoltaic performances with the best porphyrin, LD14, showing J(SC) = 19.167 mA cm(-2), V(OC) = 0.736 V, FF = 0.711, and overall power conversion efficiency eta = 10.17%.
Cooperativity and Site-Selectivity of Intramolecular Hydrogen Bonds on the Fluorescence Quenching of Modified GFP Chromophores
(2015-12-18)
Chang, Deng-Hsiang
;
Ou, Chun-Lin
;
Hsu, Hung-Yu
;
Huang, Guan-Jhih
;
Kao, Chen-Yi
This paper provides the first example of experimentally characterized hydrogen-bond cooperativity on fluorescence quenching with a modified green fluorescence protein (GFP) chromophore that contains a 6-membered C=N center dot center dot center dot H-O and a 7-membered C=O center dot center dot center dot H-O intramolecular H-bonds. Variable-temperature H-1 NMR and electronic absorption and emission spectroscopies were used to elucidate the preference of intra- vs intermolecular H-bonding at different concentrations (1 mM and 10 mu M), and X-ray crystal structures provide clues of possible intermolecular H-bonding modes. In the ground state, the 6-membered H-bond is significant but the 7-membered one is rather weak. However, fluorescence quenching is dominated by the 7-membered H-bond, indicating a strengthening of the H-bond in the excited state. The H-bonding effect is more pronounced in more polar solvents, and no intermediates were observed from femtosecond fluorescence decays. The fluorescence quenching is attributed to the occurrence of diabatic excited-state proton transfer. Cooperativity Of the two intramolecular H-bonds on spectral shifts and fluorescence quenching is evidenced by comparing with both the single H-bonded and the non-H-bonded counterparts. The H-bond cooperativity does not belong to the conventional patterns of sigma- and pi-cooperativity but a new type of polarization interactions, which demonstrates the significant interplay of H-bonds for multiple H-bonding systems in the electronically excited states.
Effects of Hydrogen Bonding on Internal Conversion of GFP-like Chromophores. I. The para-Amino Systems
(2013-03-07)
Huang, Guan-Jhih
;
Cheng, Chi-Wen
;
Hsu, Hung-Yu
;
Prabhakar, Ch.
;
Lee, Yuan-Pern
To understand the effects of solvent-solute hydrogen bonding (SSHB) on the excited-state dynamics of two GFP-like chromophores, p-ABDI and p-CFABDI, we have determined the quantum yields for fluorescence (Phi(f)) and the isomerization Z -> E (Phi(ZE)) and the femtosecond fluorescence and transient infrared absorption in selected solvents. The behavior that Phi(ZE) congruent to 45 0.50 in aprotic solvents, such as CH3CN, indicates that the E-Z photoisomerization adopts a one-bond-flip mechanism through the torsion of the exocyclic C=C bond (the tau torsion) to form a perpendicular species (tau similar to 90 degrees) in the singlet excited state followed by internal conversion (IC) to the ground state and partition to form the E and Z isomers with equal probabilities. The observed Phi(ZE) decreased from 0.50 to 0.15-0.28 when CH3CN was replaced with the protic solvents CH3OH and CF3CH2OH. In conjunction with the solvent-independent rapid (<1 ps) kinetics for the fluorescence decay and the solvent-dependent slow (7-20 ps) kinetics for the ground-state recovery, we conclude that the SSHB modifies the potential energy surface for the tau torsion in a way that the IC occurs also for the twisted intermediates with a tau-torsion angle smaller than 90 degrees, which favors the formation of the Z isomers. The possibility of IC induced by torsion of the exocyclic C-C bond (the phi torsion) is also considered but excluded.
Effects of Hydrogen Bonding on Internal Conversion of GFP-like Chromophores. II. The meta-Amino Systems
(2013-03-07)
Cheng, Chi-Wen
;
Huang, Guan-Jhih
;
Hsu, Hung-Yu
;
Prabhakar, Ch.
;
Lee, Yuan-Pern
To rationalize the efficient quenching of the fluorescence and the Z -> E photoisomerization of m-ABDI, the meta-amino analogue of the green fluorescent protein (GFP) chromophore, in protic solvents, the femtosecond time-resolved fluorescence and transient infrared (TRIR) spectra of m-ABDI in CD3CN, CH3OH, and CD3OD are determined. For solutions in CD3CN, the fluorescence decay lifetime is similar to 7.9 ns and IR absorption lines near 1513, 1531, 1557, and 1613 cm(-1) of m-ABDI in its electronically excited state were observed with a decay time >5 ns. For solutions in CH3OH, the fluorescence decay is double exponential with time constants of similar to 16 and 62 ps. In addition to IR absorption lines of m-ABDI in its electronically excited state with a decay time of similar to 16 ps, new features near 1513, 1532, 1554, and 1592 cm(-1) were observed to have a rise time of similar to 19 ps and a decay constant of similar to 58 ps, indicating formation of an intermediate. The assignments for the IR spectra of the ground and excited states were assisted with DFT and TDDFT calculations, respectively. We conclude that the torsion of the exocyclic C=C bond (the tau torsion) is responsible for the nonradiative decay of electronically excited m-ABDI in CD3CN. However, in CH3OH and CD3OD, the solute-solvent hydrogen bonding (SSHB) interactions diminish significantly the barrier of the tau torsion and induce a new pathway that competes successfully with the tau torsion, consistent with the efficient fluorescence quenching and the diminished yield for Z -> E photoisomerization. The new pathway is likely associated with excited state proton transfer (ESPT) from the solvent to m-ABDI, particularly the carbonyl group, and generates an intermediate (ESPT*) that is weakly fluorescent.
Electroabsorption spectra of push-pull porphyrins in solution and in solid films
(2015-01-01)
Awasthi, Kamlesh
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Hsu, Hung-Yu
;
Chiang, Hung-Chu
;
Mai, Chi-Lun
;
Yeh, Chen-Yu
Polarized electroabsorption (E-A) spectra of highly efficient porphyrin sensitizers (YD2 and YD2-oC8) have been measured in benzene solution. Polarized E-A spectra of these push-pull porphyrins embedded in poly(methyl methacrylate) films or sensitized on TiO2 films are also observed. Based on the analysis of the E-A spectra, the magnitude of the electric dipole moment both in the ground state and in the lowest excited state have been evaluated in solution and in solid films. The electric dipole moment in the excited state of these compounds is very large on TiO2 films, suggesting the interfacial charge transfer on TiO2 surface following photoexcitation of porphyrin dyes. The electric dipole moment in the excited state evaluated from the E-A spectra is very different from the one evaluated from the electrophotoluminescence spectra on TiO2, suggesting that the strong local field of TiO2 films is applied to the fluorescing dyes attached to TiO2 films.
Enhanced charge transfer character of photoexcited states of dye sensitizer on the N719/TiO2 interface as revealed by electroabsorption spectra
(2014-08-15)
Awasthi, Kamlesh
;
Hsu, Hung-Yu
;
Diau, Eric Wei-Guang
;
Ohta, Nobuhiro
;
應用化學系
Electroabsorption (E-A) spectra of (Bu4N)(2)[Ru(dcbpyH)(2)(NCS)(2)] (N719) sensitized on TiO2 nanoparticles are very different from those of the N719 solid film. In contrast with N719 fixed in a solid form, N719 adsorbed on TiO2 shows a significant electric field effect on absorbance, indicating the strong interaction in the surface between N719 and TiO2. The magnitude of the change in electric dipole moment following absorption of N719 sensitized on TiO2 is much greater than that of the sold film, suggesting that the interfacial charge transfer occurs following photoexcitation of N719 adsorbed on TiO2 surface. (C) 2014 Elsevier B.V. All rights reserved.
Excited state dynamics of green fluorescence protein chromophore derivatives investigated with time-resolved fluorescence and transient infrared absorption
(2012-08-19)
Cheng, Chi-Wen
;
Hsu, Hung-Yu
;
Huang, Guan-Jhih
;
Diau, Eric Wei-Guang
;
Yang, Jye-Shane
Femtosecond Excitonic Relaxation Dynamics of Perovskite on Mesoporous Films of Al2O3 and NiO Nanoparticles
(2014-08-25)
Hsu, Hung-Yu
;
Wang, Chi-Yung
;
Fathi, Amir
;
Shiu, Jia-Wei
;
Chung, Chih-Chun
The excitonic relaxation dynamics of perovskite adsorbed on mesoporous thin films of Al2O3 and NiO upon excitation at 450 nm were investigated with femtosecond optical gating of photoluminescence (PL) via up-conversion. The temporal profiles of emission observed in spectral region 670-810 nm were described satisfactorily with a composite consecutive kinetic model and three transient components representing one hot and two cold excitonic relaxations. All observed relaxation dynamics depend on the emission wavelength, showing a systematic time-amplitude correlation for all three components. When the NiO film was employed, we observed an extent of relaxation proceeding through the non-emissive surface state larger than through the direct electronic relaxation channel, which quenches the PL intensity more effectively than on the Al2O3 film. We conclude that perovskite is an effective hole carrier in a p-type electrode for NiO-based perovskite solar cells showing great performance.
Femtosecond Infrared Transient Absorption Dynamics of Benzimidazole-Based Ruthenium Complexes on TiO2 Films for Dye-Sensitized Solar Cells
(2014-07-31)
Hsu, Hung-Yu
;
Cheng, Chi-Wen
;
Huang, Wei-Kai
;
Lee, Yuan-Pern
;
Diau, Eric Wei-Guang
By means of femtosecond infrared transient absorption spectra, we measured the interfacial electron-transfer dynamics for benzimidazole-based heteroleptic ruthenium dyes (RIDS, RD12, RD15-RD18) sensitized on TiO2 thin films. For all measurements, the first singlet metal-to-ligand charge-transfer states ((MLCT)-M-1) of the ruthenium complexes were excited at 519 nm and the injected electrons in the conduction band of TiO2 were probed at 4.3 mu m. All transient signals featured two rising components on a femtosecond-picosecond scale due to a two-step electron injection and an offset (N719, RD16-RD18) or a slow-decay (RD5, RD12, and RD15) component on a nanosecond microsecond scale due to a back electron transfer. A complicated two-step kinetic model was derived analytically to interpret the observed two rising components for which the rapid (tau(1) < 300 fs) and slow (tau(2) = 10-20 ps) electron injections arose from the singlet (MLCT)-M-1 and triplet (MLCT)-M-3 states, respectively. The amplitudes of the two electron-injection components (A(1) and A(2)) were controlled by the rate coefficient of the (MLCT)-M-1 --> (MLCT)-M-3 intersystem crossing; the variations of A(1) and A(2) are consistent with the trend of the corresponding Stokes shifts rationalized with a conventional energy-gap law for nonradiative transitions. Compared with the kinetics observed for the N719 dye, the involvement of a benzimidazole ligand in RD dyes had the effect of accelerating the two electron injections, thus improving the short circuit current of the device. RD dyes substituted with fluorine atoms and/or thiophene units in the benzirnidazole ligands showed a retardation of 3MLCT electron injection relative to that of the nonsubstituted RD5 dye. Acceleration of the BET process was observed for the RD5 dye (9 ns), and both fluoro-substituted dyes (14 ns for RD12 and 21 ns for RD15) and thiophene-substituted dyes (nonobservable for RD16-RD18) had significantly retarded BET kinetics. The observed kinetics of the (MLCT)-M-3 electron injection for all RD dyes is satisfactorily simulated with the Marcus theory.
Femtosecond Infrared Transient Absorption Dynamics of Benzimidazole-Based Ruthenium Complexes on TiO2 Films for Dye-Sensitized Solar Cells
(2014-07-31)
Hsu, Hung-Yu
;
Cheng, Chi-Wen
;
Huang, Wei-Kai
;
Lee, Yuan-Pern
;
Diau, Eric Wei-Guang
By means of femtosecond infrared transient absorption spectra, we measured the interfacial electron-transfer dynamics for benzimidazole-based heteroleptic ruthenium dyes (RIDS, RD12, RD15-RD18) sensitized on TiO2 thin films. For all measurements, the first singlet metal-to-ligand charge-transfer states ((MLCT)-M-1) of the ruthenium complexes were excited at 519 nm and the injected electrons in the conduction band of TiO2 were probed at 4.3 mu m. All transient signals featured two rising components on a femtosecond-picosecond scale due to a two-step electron injection and an offset (N719, RD16-RD18) or a slow-decay (RD5, RD12, and RD15) component on a nanosecond microsecond scale due to a back electron transfer. A complicated two-step kinetic model was derived analytically to interpret the observed two rising components for which the rapid (tau(1) < 300 fs) and slow (tau(2) = 10-20 ps) electron injections arose from the singlet (MLCT)-M-1 and triplet (MLCT)-M-3 states, respectively. The amplitudes of the two electron-injection components (A(1) and A(2)) were controlled by the rate coefficient of the (MLCT)-M-1 --> (MLCT)-M-3 intersystem crossing; the variations of A(1) and A(2) are consistent with the trend of the corresponding Stokes shifts rationalized with a conventional energy-gap law for nonradiative transitions. Compared with the kinetics observed for the N719 dye, the involvement of a benzimidazole ligand in RD dyes had the effect of accelerating the two electron injections, thus improving the short circuit current of the device. RD dyes substituted with fluorine atoms and/or thiophene units in the benzirnidazole ligands showed a retardation of 3MLCT electron injection relative to that of the nonsubstituted RD5 dye. Acceleration of the BET process was observed for the RD5 dye (9 ns), and both fluoro-substituted dyes (14 ns for RD12 and 21 ns for RD15) and thiophene-substituted dyes (nonobservable for RD16-RD18) had significantly retarded BET kinetics. The observed kinetics of the (MLCT)-M-3 electron injection for all RD dyes is satisfactorily simulated with the Marcus theory.
Field-Induced Fluorescence Quenching and Enhancement of Porphyrin Sensitizers on TiO2 Films and in PMMA Films
(2013-11-28)
Hsu, Hung-Yu
;
Chiang, Hung-Chu
;
Hu, Jyun-Yu
;
Awasthi, Kamlesh
;
Mai, Chi-Lun
Three highly efficient porphyrin sensitizers-YD2, YD2-oC8, and YD30, either sensitized on TiO2 films or embedded in PMMA films were investigated using electrophotoluminescence (E-PL) spectra. Under both thin-film conditions, on application of an external electric field we observed the quenching of fluorescence of push-pull porphyrins (YD2 and YD2-oC8) and a slightly enhanced fluorescence of the reference porphyrin without an electron donor group (YD30). A nonfluorescent state with charge separation (CS) is proposed to be involved in both YD2 and YD2-oC8 systems so that the electron injection becomes accelerated in the presence of a strong electric field. In contrast, the retardation of the nonradiative process not involving a CS state was the reason for the field-induced enhancement of fluorescence of YD30. The extent of fluorescence quenching of YD2-oC8 was greater than that of YD2 on TiO2 films, indicating that the ortho-substituted long alkoxyl chains play a key role to accelerate the consecutive electron injection involving the CS state. Our E-PL results indicate that a field-induced variation of fluorescent intensity is related to the efficiency of conversion of solar energy and that further improvement of the performance of devices containing push pull porphyrin dyes is achievable under an applied electric field.
Panchromatic co-sensitization of porphyrin-sensitized solar cells to harvest near-infrared light beyond 900 nm
(2015-01-01)
Shiu, Jia-Wei
;
Chang, Yen-Cheng
;
Chan, Chien-Yi
;
Wu, Hui-Ping
;
Hsu, Hung-Yu
We designed a dimeric porphyrin dye (LDD1) based on an efficient push-pull zinc porphyrin (LD14) with extended pi-conjugation through coupling of two zinc porphine cores via an acetylene bridge at the meso position of the porphyrin to extend the absorption spectrum effectively into the near infrared region. The effect of dye aggregation among porphyrin molecules was significantly suppressed when the LDD1 and LD14 dyes were co-sensitized on a nanocrystalline TiO2 film in a dye-sensitized photovoltaic system. The light-harvesting ability of the device exhibits a panchromatic feature covering a broad spectral region from 400 nmto 900 nm, which results in a short-circuit current density of 21.3 mA cm(-2) and a power conversion efficiency of 10.4% in an iodine-based solar cell.
Using Gold Nanoclusters As Selective Luminescent Probes for Phosphate-Containing Metabolites
(2012-07-03)
Li, Po-Han
;
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.