Morton Z. Hoffman

Rate Constants for the Quenching of Excited States of Metal Complexes in Fluid Solution

The rate constants for the quenching of the excited states of metal ions and complexes in homogeneous fluid solution are reported in this compilation. Values of kq for dynamic, collisional processes between excited species and quenchers have been critically evaluated, and are presented with the following information, among others, from the original publications, when available: description of the solution medium, temperature at which kq was determined, experimental method, range of quencher concentration used, lifetime of the excited state in the absence of quencher, activation parameters, quenching mechanism. Data collection is complete through the end of 1986, and covers the coordination compounds of 26 metals, including the ions and complexes of the inner‐ and outer‐transition metals, and porphyrin complexes of nontransition metals. Data for 261 excited states quenched by more than 400 inorganic quenchers and 600 organic quenchers have been extracted from almost 500 publications. The introduction to th...

An evaluation of the excited state absorption spectrum of Ru(bpy)32+ in aqueous and acetonitrile solutions

Abstract Three pulsed laser techniques have been used to evaluate the absorption spectrum of ★Ru(bpy) 3 2+ in H 2 O, CH 3 CN and H 2 O/CH 3 CN mixtures: complete conversion of the ground state, energy transfer to anthracene, and benzophenone actinometry. The three techniques give reliable and reproducible values of ϵ 450 =4.6(±0.4) × 10 3 M −1 cm −1 , independent of the solution medium. The ground state spectrum is virtually the same in H 2 O and CH 3 CN with ϵ 452 = 1.46 × 10 4 M −1 cm −1 ; the value of ϵ 450 , the difference in the ϵ values of the excited and the ground states at 450 nm, is −1.0(±0.09)×10 4 M − cm −1 . Ru(bpy) 3 2+ can serve as a reliable actinometer for the 532 nm frequency doubled Nd:YAG pulsed laser line and, with appropriate corrections for the inner filter effect, for the 355 nm frequency tripled line.

EFFECT OF SOLUTION MEDIUM ON THE RATE CONSTANTS OF EXCITED-STATE ELECTRON-TRANSFER QUENCHING REACTIONS OF RUTHENIUM(II)-DIIMINE PHOTOSENSITIZERS

Abstract In this paper, we review the effects of solution medium (pH, solvent, temperature, ionic strength, specific electrolytes) on the oxidative and reductive quenching rate constants k q of the excited states of Ru(II)-diimine photosensitizers. Diffusion of the donor and acceptor species together to form the precursor complex ( k et ) and electron transfer within the complex ( k et ) contribute to the value of k q . Values of k d vary with bulk solution properties; variations of k et can be described within the context of Marcus theory, wherein dynamic solvent effects influence the nuclear frequency factor and electronic coupling, and static properties cause changes in the driving force of electron transfer ΔG et o and the reorganization energy λ. The pH can affect the state of protonation of the excited photosensitizer and/or the quencher, thereby altering k et through changes in ΔG ct o and k d through changes in the charges of the reactants. Ionic species are ion-paired by the dominant counterion; the Olson-Simonson treatment allows the electron transfer components of quenching for ion-paired ( k ip ) and nonion-paired ( k mp ) species to be extracted. The quenching of ∗ Ru(bpy) 3 2+ by methylviologen is used to demonstrate specific salt effects, which result in variations in λ; λ is lowest, and k q highest, for the anions with the most weakly-held hydration spheres and the strongest structure-breaking abilities (e.g. ClO 4 − , I − ). Quenching rate constants can be fine-tuned through the variation of solvent, pH, electrolyte, ionic strength, and temperature.

ANION AND SOLVENT EFFECTS ON THE RATE OF REDUCTION OF TRIPLET EXCITED THIAZINE DYES BY FERROUS IONS

Abstract— The lifetimes of the triplet excited states of thionine and methylene blue were measured in aqueous and 50 v/v% aqueous acetonitrile solutions acidified with 0.01 N sulfuric or trifluoromethyl‐sulfonic acid. The rate constants for reaction of the triplet excited dyes with ferrous ions were measured in the same solutions. The triplet lifetimes in the absence of added quenchers were insensitive to a change in acid from trifluoromethylsulfonic to sulfuric or to a change in solvent from water to 50v/v% aqueous acetonitrile (τ for triplet thionine ˜7.5 μs, τ for triplet methylene blue ˜4.5 μs). In contrast, the rate constant for reaction of the triplet dyes with ferrous ions increased by nearly a factor of 10 with a change in acid from trifluoromethylsulfonic to sulfuric. In solutions containing sulfate ions this reaction rate constant increased with increasing sulfate concentration and with a change in solvent from water to 50 v/v% aqueous acetonitrile. The results are discussed in terms of the possibility of association of the positively charged reactive ions with sulfate anions. Quenching of the triplet excited dyes by ferric ions or by ground state dye molecules was shown to be negligible at the concentration used for the ferrous ion quenching study.

Effect of pH on the Reactivity of the Carbonate Radical in Aqueous Solution

The rate constants for the reaction of

Cr(bpy)33+-sensitized photo-oxidation of phenol in aqueous solution

{\rm CO}_{3}{}^{-}

Radiolytically-induced one-electron reduction of methyl viologen in aqueous solution: Stability of the radical cation in acidic and highly alkaline media(1)

radicals, generated in aqueous solution by the flash photolysis of

Solvent isotope effect on the photophysics of Ru(bpy)32+ and Ru(phen)32+ in aqueous solution at room temperature

{\rm Co}({\rm NH}_{3})_{4}{\rm CO}_{3}{}^{+}

Interaction of radiation-generated radicals with myoglobin in aqueous solution—II: Analysis of product yields for hydroxyl radicals with oxymyoglobin under deaerated conditions

, with some sulfur-containing compounds, some amino acids and enzymes, and nitromethane have been measured. The radical is significantly more reactive with the deprotonated sulfhydryl group than with the protonated form. The presence of an amino group causes the rate constant to diminish upon deprotonation. The radical is more reactive with the deprotonated imidazole ring in histidine than with the protonated form. Ribonuclease A and tyrosine show the same reactivity pattern with the radical; deprotonation of the phenolic groups in tyrosine increases the value of the rate constant. Lysozyme and α-chymotrypsin show pH-independent values. Finally,

Protonation of the ground states of ruthenium(II) photosensitizers

{\rm CO}_{3}{}^{-}