Salt Effects on the Charge Separation Yield in Photoinduced Electron Transfer Reactions: The Effect of Excited State Multiplicity

2001 ◽  
Vol 26 (2-3) ◽  
pp. 263-276 ◽  
Author(s):  
Vicente Avila ◽  
Carlos A. Chesta ◽  
Carlos M. Previtali
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Charge Separation ◽  
Photoinduced Electron Transfer ◽  
Transfer Reactions ◽  
Salt Effects ◽  
Electron Transfer Reactions ◽  
State Multiplicity

Transient states in photoinduced electron transfer reactions of porphyrin- and phthalocyanine-fullerene dyads

2009 ◽  
Vol 13 (10) ◽  
pp. 1090-1097 ◽  
Author(s):  
Helge Lemmetyinen ◽  
Nikolai Tkachenko ◽  
Alexander Efimov ◽  
Marja Niemi
Keyword(s):  
Electron Transfer ◽  
Charge Separation ◽  
Photoinduced Electron Transfer ◽  
Transient State ◽  
Primary Electron ◽  
Transfer Reactions ◽  
Acceptor Pair ◽  
Electron Transfer Reactions ◽  
Exciplex Formation ◽  
Donor And Acceptor

This paper combines the most important results on studies performed by the authors during the last decade on photoinduced electron transfer reactions of pheophytin-, phthalocyanine-, and porphyrin-fullerene dyads, in which donor and acceptor moieties are covalently linked to each other. Practically all studied molecules form an intramolecular exciplex as a transient state before the formation of the charge separation state or tight ion pair. When the center-to-center distance of the donor and acceptor pair is short (7–10 Å) both the exciplex formation and primary electron transfer are extremely fast with rate constants of 7–23 × 1012 s -1 and 40–1400 × 109 s -1, respectively. Rates become slower when the distance and orientational fluctuation increases. No systematic correlation between free energies and the rates of the formation and recombination of the exciplex and the charge separation state, respectively, were observed. The mechanism is discussed in frames of the Marcus electron transfer and the radiationless quantum transition theories.

Charge transfer emissive singlet excited states and photoinduced electron transfer properties in the diarylideneacetone compounds (RCHCH)2CO; R = phenyl, 1- and 2-naphthyl, 3-(N-ethylcarbazoyl), and 4-(C5H5)Fe(C5H4C6H4CHCH(CO)CHCHC6H5)

1990 ◽  
Vol 68 (12) ◽  
pp. 2278-2288 ◽  
Author(s):  
Pierre D. Harvey ◽  
Liangbing Gan ◽  
Christiane Aubry
Keyword(s):  
Electron Transfer ◽  
Excited State ◽  
Charge Transfer ◽  
Excited States ◽  
Photoinduced Electron Transfer ◽  
Flash Photolysis ◽  
Reduction Process ◽  
Transfer Reactions ◽  
Electron Transfer Reactions ◽  
Electron Reduction

Four diarylideneacetone compounds ((RCHCH)2CO, where the aryl groups are phenyl (dba), 1-naphthyl (1-dNapha), 2-naphthyl (2-dNapha), and 3-(N-ethylcarbazoyl) (dNECa)), and 4-(C5H5)Fe(C5H4C6H4CHCH(CO)CHCH(C6H5) (dba-Fc) have been prepared and characterized. The compounds are found to be fluorescent and photochemically and reversibly electrochemically active. The lowest-energy absorption bands for the diarylideneacetones are assigned to a charge transfer (CT) electronic transition, except for dba-Fc, in which a ferrocenyl ligand field transition assignment is made. The 77 K CT absorption and fluorescence bands are vibrationally structured (vibrational spacings = 1260–1360 cm−1). While the fluorescence decay at 293 K is monoexponential, the excited state fluorescence lifetimes (τF) for the 77 K samples exhibit double exponential decays, the short component being 0.38–0.64 ns and the long one 3.5–10.9 ns. The photophysical results are interpreted in terms of excited state deactivation processes dominated by radiationless pathways that are associated with the presence of fluorescent species with different geometries. Only the dNECa compound is found to be fluorescent in solution at 298 K [Formula: see text]. Cyclic voltammetry and coulometry measurements suggest that a reversible one-electron reduction process and an irreversible higher potential one-electron reduction process take place in the −1 to −2 V vs. SSCE range. In addition, dba-Fc also exhibits an electrochemically reversible one-electron oxidation wave at 0.52 V vs. SSCE centered at the ferrocenyl group. These results together with the spectroscopic electronic data have permitted evaluation of the reduction potentials of the lowest singlet (CT excited states (E1−/*);they range from 1.4 to 2.2 V vs. SSCE, with dba being the strongest photooxidizing agent and dNECa the weakest. Photoinduced intermolecular electron transfer reactions have been investigated by steady state fluorescence techniques and picosecond flash photolysis spectroscopy for dNECa and dba, respectively. The bimolecular deactivation rate constants, kq, for the reductive photoinduced electron transfer reactions of dNECa with diphenylamine (DPA) (kq = (2.65 ± 0.25) × 107 M−1 s−1) and N, N, N′, N′-tetramethylphenylenediamine (TMPM) (kq = (1.38 ± 0.03) × 108 M−1 s−1) have been obtained in THF solutions at 293 K. No fluorescence quenching is observed when oxidative and energy transfer quenchers are used with dNECa. For the non-emissive dba compound at room temperature, picosecond flash photolysis experiments show that quenching of the broad dba transient band (~500 nm) does indeed occur between 5 and 10 ns. Keywords: dibenzylideneacetone, charge transfer, photoelectron transfer.

Salt effects in photoinduced electron transfer reactions

1986 ◽  
Vol 27 (27) ◽  
pp. 3123-3126 ◽  
Author(s):  
Barbara Goodson ◽  
Gary B. Schuster
Keyword(s):  
Electron Transfer ◽  
Photoinduced Electron Transfer ◽  
Transfer Reactions ◽  
Salt Effects ◽  
Electron Transfer Reactions
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