Competition between electron transfer, trapping, and recombination in CdS nanorod–hydrogenase complexes

2015 ◽  
Vol 17 (8) ◽  
pp. 5538-5542 ◽  
Author(s):  
James K. Utterback ◽  
Molly B. Wilker ◽  
Katherine A. Brown ◽  
Paul W. King ◽  
Joel D. Eaves ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Transient Absorption ◽  
Relaxation Processes ◽  
Absorption Measurements

Kinetic modeling of transient absorption measurements provides rate constants for the excited state relaxation processes relevant for photochemical H2 generation.

scholarly journals Mechanistic Investigations of an α-Aminoarylation Photoredox Reaction

2021 ◽  
Author(s):  
Bernard Stevenson ◽  
Ethan Spielvogel ◽  
Emily Loiaconi ◽  
Victor M. Wambua ◽  
Roman Nakhamiyayev ◽  
...  
Keyword(s):  
Quantum Yield ◽  
Absorption Spectroscopy ◽  
Rate Constant ◽  
Kinetic Modeling ◽  
Rate Constants ◽  
Transient Absorption ◽  
Coupling Reaction ◽  
Time Dependent ◽  
Transient Absorption Spectroscopy ◽  
Mechanistic Investigations

We present time-dependent percent and quantum yield measurements of a photoredox-catalyzed coupling reaction between 1,4-dicyanobenzene and N-phenylpyrrolidine. We also use transient absorption spectroscopy to examine the kinetics within the reaction and use kinetic modeling to extract rate constants and predict how changes in rate constant will impact the quantum yield.

Photoinduced electron transfer dynamics in dye-sensitized ZnO nanowire photoanodes

2018 ◽  
Vol 32 (19) ◽  
pp. 1840049
Author(s):  
Akihiro Furube ◽  
Takahiro Arai ◽  
Masahiro Okazaki ◽  
Shinichiro Yanagiya ◽  
Liang-Yih Chen ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Transient Absorption ◽  
Low Cost ◽  
Transient Absorption Spectroscopy ◽  
Zno Nanowire ◽  
Dye Sensitized ◽  
Femtosecond Transient Absorption ◽  
State Formula ◽  
Flexible Solar Cell

A photoanode using dye-sensitized ZnO nanowire (NW) is a good candidate for low-cost, colorful, light-weight and flexible solar cell material. We have synthesized a ZnO NW anode and a ZnO nanowire–nanoparticle (NWNP) anode, in which ZnO nanoparticles (NPs) are decollated on the surface of NWs. Photo-induced electron transfer dynamics from the excited state of sensitizer dye (D149) to the conduction band of ZnO NW and ZnO NWNP was clarified using femtosecond transient absorption spectroscopy. The decay of the single excited state ([Formula: see text]) of D149 was faster in ZnO NW than that of ZnO NWNP, indicating that NW is more suitable as an efficient electron acceptor.

Efficient photoinduced electron transfer between C60/C70 and zinc octaethylporphyrin studied by nanosecond laser photolysis method

2000 ◽  
Vol 04 (06) ◽  
pp. 591-598 ◽  
Author(s):  
MOHAMED E. EL-KHOULY ◽  
MAMORU FUJITSUKA ◽  
OSAMU ITO
Keyword(s):  
Electron Transfer ◽  
Rate Constants ◽  
Photoinduced Electron Transfer ◽  
Transfer Rate ◽  
Transient Absorption ◽  
Laser Light ◽  
Solvent Polarity ◽  
Nanosecond Laser ◽  
Electron Transfer Rate ◽  
Absorption Bands

Photoinduced electron-transfer processes between C 60 or C 70 and zinc octaethylporphyrin ( ZnOEP ) have been studied in polar solvents with the nanosecond laser flash photolysis method, observing the transient absorption spectra in the visible and near-IR regions. By the predominant excitation of ZnOEP with 532 nm laser light the transient absorption bands of 3 ZnOEP * decayed, accompanied by the appearance of the transient absorption bands of [Formula: see text] and [Formula: see text]. By the predominant excitation of C 60 and C 70 with 610 nm laser light the decays of [Formula: see text] and [Formula: see text] were observed, accompanied by the appearance of [Formula: see text] and [Formula: see text]. The electron transfer rate constants (k et ) and the quantum yields (Φ et ) of [Formula: see text] and [Formula: see text] formation via 3 ZnOEP * and [Formula: see text] or [Formula: see text] have been evaluated. These values increase with the solvent polarity; in polar benzonitrile these values are higher than for other porphyrins such as zinc tetraphenylporphyrin. The back electron transfer rate constants were evaluated from the decays of [Formula: see text] and [Formula: see text], which also show a solvent polarity dependence.

Substituent effects on homolytic versus heterolytic photocleavage of (1-naphthylmethyl)trimethylammonium chlorides

1987 ◽  
Vol 65 (7) ◽  
pp. 1599-1607 ◽  
Author(s):  
B. Foster ◽  
B. Gaillard ◽  
N. Mathur ◽  
A. L. Pincock ◽  
J. A. Pincock ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Hydrogen Atom ◽  
Charge Distribution ◽  
Rate Constants ◽  
Bond Cleavage ◽  
Substituent Effects ◽  
Hydrogen Atom Transfer ◽  
Singlet Excited State ◽  
State Rate

Singlet excited state rate constants have been measured for both the heterolytic and homolytic photocleavage of 3- and 4-methoxy and 3- and 4-cyano (1-naphthylmethyl)trimethylammonium chlorides, 6–10. The results are interpreted in terms of the meta effect or changes in charge distribution upon excitation and the competition between bond cleavage, electron transfer, and hydrogen atom transfer in the contact pairs resulting from the two types of cleavage.

Interfacial electron transfer yields in dye-sensitized NiO photocathodes correlated to excited-state dipole orientation of ruthenium chromophores

2018 ◽  
Vol 96 (9) ◽  
pp. 865-874 ◽  
Author(s):  
Yejee Han ◽  
Robert J. Dillon ◽  
Cory J. Flynn ◽  
Eric S. Rountree ◽  
Leila Alibabaei ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Transient Absorption ◽  
Photovoltaic Performance ◽  
Interfacial Electron Transfer ◽  
Dipole Orientation ◽  
Ruthenium Polypyridyl ◽  
Dye Sensitized ◽  
Surface Enhanced ◽  
Device Efficiency

Interface dynamics of nanocrystalline NiO thin films sensitized with two ruthenium polypyridyl chromophores have been investigated to examine the influence that excited-state dipole orientation and the position of the bipyridine radical formed in the charge-separated state have on interfacial electron transfer yields. In ultrafast transient absorption experiments, the charge separated state is observed on the nanosecond timescale for the trifluoromethyl-substituted chromophore, [Ru(flpy)2(dcb)]2+ (flpy = 4,4′-bis(trifluoromethyl)-2,2′-bipyridine, dcb = 4,4′-dicarboxy-2,2′-bipyridine), but not for [Ru(bpy)2(dcb)]2+ (bpy = 2,2′-bipyridine). Differences are attributed to the positioning of the bipyridine radical formed in the charge separated state; for [Ru(flpy)2(dcb)]2+, the electron is localized on the flpy ligand distal to the surface, whereas for [Ru(bpy)2(dcb)]2+, the electron is localized on the dcb ligand, proximal to the NiO surface. Enhanced photovoltaic performance is observed for dye-sensitized solar cell devices prepared with [Ru(flpy)2(dcb)]2+, demonstrating that enhanced charge separation can be correlated with device efficiency.

Excited state electron transfer in A2 and A2B2 functionalized zinc porphyrins carrying rigid and flexible β-pyrrole π-extended substituents

2020 ◽  
Vol 24 (05n07) ◽  
pp. 904-919
Author(s):  
Michael B. Thomas ◽  
Siddhartha Kumar ◽  
Timothy Esquivel ◽  
Hong Wang ◽  
Francis D’Souza
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Transient Absorption ◽  
Binding Constants ◽  
Free Energy Calculations ◽  
Stable Complex ◽  
State Electron ◽  
Femtosecond Transient Absorption ◽  
Absorption Studies ◽  
Zinc Porphyrins

Optical absorption and emission, electrochemical, and photochemical properties of peripherally functionalized with flexible and rigid [Formula: see text]-extended substituents on A2 and A2B2 type zinc porphyrins is investigated. The significance of rigid [Formula: see text]-substituents over flexible ones in governing the spectral properties is unraveled. Flexible [Formula: see text]-substituents on the porphyrin ring caused appreciable spectral broadening compared to porphyrin carrying rigid [Formula: see text]-substituents. Further, supramolecular dyads are formed by coordinating phenyl imidazole functionalized fullerene, C[Formula: see text]Im. The calculated binding constants for the 1:1 complexes is in the order of 2–7 × 105 M[Formula: see text] suggesting stable complex formation. Free-energy calculations performed according to the Rehm–Weller approach suggested possibility of excited state electron transfer in these dyads. Femtosecond transient absorption studies of the dyads performed in [Formula: see text]-dichlorobenzene showed evidence of occurrence of electron transfer from the singlet-excited state that was in competition with the intersystem crossing process to populate the triplet-excited state of porphyrins.

Donor-acceptor conjugates derived from cobalt porphyrin and fullerene via metal-ligand axial coordination: Formation and excited state charge separation

2021 ◽  
pp. A-N
Author(s):  
Dili R. Subedi ◽  
Youngwoo Jang ◽  
Ashwin Ganesan ◽  
Sydney Schoellhorn ◽  
Ryan Reid ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Charge Separation ◽  
Transient Absorption ◽  
Transient Absorption Spectroscopy ◽  
Cobalt Porphyrin ◽  
Axial Coordination ◽  
Cobalt Porphyrins ◽  
Donor Acceptor ◽  
Metal Ligand

Two types of cobalt porphyrins, viz., meso-tetrakis(tolylporphyrinato)cobalt(II), (TTP)Co (1), and meso-tetrakis(triphenylamino porphyrinato)cobalt(II), [(TPA)4P]Co, (2) were self-assembled via metal-ligand axial coordination of phenyl imidazole functionalized fulleropyrrolidine, ImC[Formula: see text] to form a new series of donor–acceptor constructs. A 1:2 complex formation with ImC[Formula: see text] was established in the case of (TTP)Co while for [(TPA)4P]Co only a 1:1 complex was possible to positively identify. The binding constants [Formula: see text] and [Formula: see text] for step-wise addition of ImC[Formula: see text] to (TTP)Co were found to be 1.07 × 105 and 3.20 × 104 M[Formula: see text], respectively. For [(TPA)4P]Co:ImC[Formula: see text], the measured [Formula: see text] values was found to be 6.48 × 104 M[Formula: see text], slightly smaller than that observed for (TTP)Co. Although both cobalt porphyrins were non-fluorescent, they were able to quench the fluorescence of ImC[Formula: see text] indicating occurrence of excited state events in the supramolecular donor-acceptor complexes. Electrochemistry coupled with spectroelectrochemistry, revealed the formation of cobalt(III) porphyrin cation instead of a cobalt(II) porphyrin radical cation, as the main product, during oxidation of phenyl imidazole coordinated cobalt porphyrin. With the help of computational and electrochemical results, an energy level diagram was constructed to witness excited state photo-events. Competitive energy and electron transfer from excited CoP to coordinated ImC[Formula: see text], and electron transfer from Im1C[Formula: see text]* to cobalt(II) porphyrin resulting into the formation of PCo[Formula: see text]:ImC[Formula: see text] charge separated state was possible to envision from the energy diagram. Finally, using femtosecond transient absorption spectroscopy and data analysis by Glotaran, it was possible to establish sequential occurrence of energy transfer and charge separation processes. The lifetime of the final charge separated state was [Formula: see text] 2 ns. A slightly better charge stabilization was observed in the case of [(TPA)4P]Co:ImC[Formula: see text] due to the presence of electron rich, peripheral triphenylamine substituents on the cobalt porphyrin.

Intramolecular photoinduced electron-transfer processes in buta-1,3-diynyl-benzene-linked porphyrin-fullerene dyad

2007 ◽  
Vol 11 (06) ◽  
pp. 397-405 ◽  
Author(s):  
Ken-ichi Yamanaka ◽  
Mamoru Fujitsuka ◽  
Yasuyuki Araki ◽  
Kentaro Tashiro ◽  
Azumi Sato ◽  
...  
Keyword(s):  
Electron Transfer ◽  
Transient Absorption ◽  
Flash Photolysis ◽  
Laser Flash Photolysis ◽  
Phenyl Group ◽  
Laser Flash ◽  
Ion Pair ◽  
Intramolecular Electron Transfer ◽  
Electron Transfer Processes ◽  
Absorption Measurements

Intramolecular electron-transfer process of porphyrin-fullerene dyad linked by phenyl buta-1,3-diynyl-phenyl unit ( ZnP - sp - C 60) was studied by laser flash photolysis. Picosecond fluorescence lifetime and transient absorption measurements revealed that photoinduced charge-separation takes place via the excited singlet state (1 ZnP *) with the rate constant of (1-2) × 1010 s −1. For the charge recombination, about a half of the radical-ion pair decayed quickly with 2.9 × 109 s −1 as evaluated from picosecond transient absorption measurements, whereas the remaining half was long-lived with slow decay (1.6 × 106 s −1) as estimated from nanosecond transient absorption measurements. The lifetime of the radical-ion pair of ZnP - sp - C 60 was longer than those of directly connected dyads with a buta-1,3-diynyl bridge and buta-1,3-diynyl-phenyl bridge by the insertion of an extra phenyl group in addition to the pyrrodino ring.

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