ISSN:0021-2148    

DOI:10.1002/ijch.198200017

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY

摘要:

AbstractThe photophysical and electron transfer properties of the following Ru(II) complexes have been characterized: Ru(bpy)3‐n(biq)2+n, Ru(bpy)2(Cl2‐bpy)2+, Ru(Cl2‐bpy)2+3, Ru(bpy)2(NO2‐bpy)2+, Ru(NO2‐bpy)2+3, Ru(bpy)2(opdi)2+, Ru(bpy)2(phedi)2+, wheren= 1 to 3, bpy = 2,2′‐bipyridine, biq = 2,2′‐biquinoline, and opdi and phedi are o‐quinodiimine ligands. The properties of these and other Ru‐polypyridine type photosensitizers are discussed on the basis of the requirements needed to split water with solar energy in an efficient way. It is shown that the Ru(bpy)2(LL)2+complexes, where LL is a polypyridine‐type ligand which is easier to reduce than bpy, are expected to be more efficient photosens

ISSN:0021-2148    

DOI:10.1002/ijch.198200018

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY

摘要:

AbstractThe properties of polypyridyl complexes of Cr(III), Cr(NN)3+3, are examined with regard to the photochemical determinants of efficient solar energy utilization and compared with those of corresponding complexes of Ru(II), Fe(II), Os(II), Rh(III), and Ir(III). The following characteristics are discussed: absorption spectra, nature and lifetimes of excited states, intersystem crossing efficiency between lowest spin‐allowed and spin‐forbidden excited states, energetics and kinetics of excited‐state redox quenching, and the properties of redox‐generated energy‐rich charge‐carriers. Recent results dealing with the effect of solution medium on intersystem crossing efficiency and excited‐state lifetimes are presented. Cr(NN)3+3complexes have been applied to solar energy conversion schemes and a brief review and critique are offered. The advantages and disadvantages of Cr(NN)3+3as solar energy harvesters and electron‐transfer mediators are discussed in terms of future rese

ISSN:0021-2148    

DOI:10.1002/ijch.198200019

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY

摘要:

AbstractIrradiation of polypyridineruthenium(II) complexes (RuL2+3) in aqueous solutions containing ascorbate (HAs−) and Lî (2,2′‐bipyridine or other polypyridines) with visible light yields reduced polypyridine LîH2and H2. The quantum yield of H2is increased greatly when cobalt(II) is also present and is optimal, Φ = 0.13, with L = bpy, Lî = 4,4′‐(CH3)2bpy (2 × 10−3M), [Co(II)] = 0.01 M, [HAs−] = 0.7 M at pH 4.5–5.5. The quantum yield of LîH2is ≧ 0.01 when Lî = bpy at ≧ 10−3M, [HAs−] = 0.7 M at pH ∼ 5 but diminishes greatly at pH ≧ 6 or when cobalt(II) is present. The photochemical experiments and pulse‐radiolysis studies indicate that the quantum yields reflect the relative rates of some twenty elementary reactions. The rate constant for the first, quenching of *RuL2+3by HAs−to give RuL+3and ascorbate radical, spans the range 0.2 × 107M−1s−1(L = 4,4‐(CH3)2bpy) to 1.1 × 109M−1s−1(L = 5‐(Cl)phen). In the absence of Co(II), RuL+3reduces LîH+and formation of LîH2(in competition with oxidation of LîH by ascorbate radical) ensues. When Co(II) is present, Co(Lî)2+ncomplexes are reduced by RuL+3to cobalt(I) complexes Co(Lî)+n. These may react with H+to form cobalt hydride complexes which undergo further reaction with H2O, H+or Co(Lî)2H2+to produce H2. At high pH, however, these reactions are too slow to compete with oxidation of cobalt(I) (k∼ 1010M−1s−1) and the hydride complexes by ascorbate radical. By contrast, at pH<4 the H2yield

ISSN:0021-2148    

DOI:10.1002/ijch.198200020

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY

摘要:

AbstractThe technique of simultaneous pulse radiolysis and photolysis, PRAP, has been utilized to study the reactions of various radicals with ground state ZnTPPS and the triplet state ZnTPPSTin aqueous solutions. The radicals H and OH add to both states withk∼ 1 × 1010M−1s−1. The CH2C(CH3)2OH radical from t‐BuOH is relatively inert toward ZnTPPS but reacts rapidly (k= 1.8 × 109M−1s−1) with ZnTPPSTto form an adduct. Electron transfer reactions are found to be about an order of magnitude faster with the triplet than with the ground state. The (CH3)2COH radical reduces both ZnTPPS (k= 1 × 108M−1s−1) and ZnTPPST(k= 3 × 109M−1s−1) to the anion radical (ZnTPPS)−. The radical Br−2oxidizes both states to the cation radical (ZnTPPS)+withk= 8 × 108M−1s−1for the ground state and 5 × 109M−1s−1for the triplet. The transient cation Cd+reduces both states with a diffusion‐controlled rate (k= 1 × 1010M−1s−1) to produce the anion radical. The above mechanisms of radical addition and electron transf

ISSN:0021-2148    

DOI:10.1002/ijch.198200021

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY

摘要:

AbstractThe triplet state of N,N,Nî,Nî‐tetraethyloxonine, TEO+generated by means of sensitization with 9,10‐dibromoanthracene, was investigated in ethanol solution by laser flash photolysis‐kinetic spectrometry employing the first harmonic of a Q‐switched ruby laser at 347.2 nm. Quenching of both the protonated triplet, TEOH2+(T1), τ = 47 μs, and the unprotonated triplet, TEO+(T1), τ = 285 μs, by TEO+(S0) proceeds with substantial net electron transfer. No net electron transfer is detectable in the quenching of TEOH2+(T1), and TEO+(T1) by O2or 1,3,5,7‐cyclooctatetraene, processes which apparently involve transfer of energy. Specific rates of quenching are reported and the implications of the quenching processes for stability of TEO+in devices for conversion or storage of solar energ

ISSN:0021-2148    

DOI:10.1002/ijch.198200022

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY

摘要:

AbstractThe influence of electron relay redox potential (E1/2) on the electron‐transfer reactions occurring in the photo‐induced hydrogen generation from water has been investigated using the Ru(bipy)2+3/MV2+/EDTA/colloidal Pt model system. Quenching rate constantskqfor electron transfer quenching of Ru(bipy)2+*3by a series of 2,2′‐ and 4,4′‐bipyridinium ions and by a series of phenanthroline ions having different redox potentialE1/2have been determined by laser flash spectroscopy in deaerated aqueous solutions at pH 5. The rate constantskbof the back electron transfer following the quenching reaction have been obtained for five bipyridinium ions under the same experimental conditions. Our results show that: (1) for the sameE1/2, the quencher molecular structure of the two homogeneous series does not affectkqsignificantly; (2) for the two series,kqincreases with increasingE1/2up to a value which is close to the diffusion‐controlled limit. The same correlation betweenkqandE1/2is obtained for the two series. Such a correlation is satisfactorily interpreted in the frame of existing theories describing electron‐transfer reactions, particularly with the Rehm‐Weller treatment, provided that an intrinsic barrier ΔG*(0) = 5.2 kcal. M−1is used; (3)kbis close to the diffusion‐controlled limit forE1/2comprised between ‐ 0.33 and ‐ 0.65 V (vs NHE); (4) a correlation between H2production rates andE1/2is suggested, and a maximum H2production is observed forE1/2≃ −0.45 V (vs. NHE) co

ISSN:0021-2148    

DOI:10.1002/ijch.198200023

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY

摘要:

AbstractPulsed laser photolysis experiments are carried out in lipid bilayer vesicles in which the fluorescence of excited pyrene (P), pyrene‐ethanol (P‐CH2OH) and pyrene‐monosulphonate (P‐SO−3) are quenched by N.N‐diethylaniline (DEA). The observed photochemical patterns are basically different from those encountered in homogeneous solutions: No detectable exciplex emission is observed, and the yield of the separated ions P−+ DEA+is small. Two alternative explanations are given for the complete lack of an exciplex fluorescence in the vesicles. One involves the requirement of a highly polar environment around the reacting species in the membrane interior. More plausibly, serious limitations imposed by the “liquid crystal” membrane microenvironment on the relative orientation of the1P* acceptor and the DEA donor, must be assumed. The quenching process leads to the formation of the P−+ DEA+radical ion pair and of the pyrene triplet state3P*. An analysis of the submicrosecond ions decay process, including its behaviour around the phase transition point of the lipids, indicates that the ions do not escape the vesicle and recombine by an intravesicle diffusion process. The relatively small yield of P−and DEA+is attributed to a microviscosity effect, inhibiting the primary separation of the solvent‐shared ion pair {P−… DEA+}. An analysis of temperature (phase transition) and external magnetic field effects indicates that the pyrene triplet state,3P*, is generated by geminate recombination in a geometrically correlated radical pair [P−… DEA+]. The results bear on the general problem of photoinduced charge separation in nonisotropic media and o

ISSN:0021-2148    

DOI:10.1002/ijch.198200024

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY

摘要:

AbstractPolymers containing pendant viologen groups were prepared and studied for their quenching efficiencies of the Ru(bpy)2+3excited state, their back reactions following the quenching, their viologen radical yields, and finally for their effectiveness in hydrogen production in the presence of colloidal platinum. Results are compared with those from methyl viologen containing systems to evaluate the performance of the polymeric viologen systems.

ISSN:0021-2148    

DOI:10.1002/ijch.198200025

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY

摘要:

AbstractA photoelectron transfer system containing the photosensitizer tris (2,2′‐bipyridyne) ruthenium II chloride, and the quencher N, Nî, di(4‐sulfonato toluyl) 4,4′‐bipyridine is described. Following a laser pulse the exited state of the photosensitizer is quenched by BSV giving a net yield of electron transfer of about 0.1. Addition of the polyelectrolyte polyvinyl sulfate (PVS) markedly enhances the rate of quenching. The decay of the electron transfer products Ru(bpy)3+3and BSV+is considerably retarded in the same system upon addit

ISSN:0021-2148    

DOI:10.1002/ijch.198200026

出版商:WILEY‐VCH Verlag    

年代:1982

数据来源: WILEY