Jan S. Jaworski

Photoinduced energy and electron transfer in 1,8-naphthalimide–corrole dyads

A series of corrole-1,8-naphthalimide dyads has been synthesized. The dyads were assembled in a convergent fashion from two fragments via a corrole forming reaction. Central to the success of the synthetic strategy was the preparation of suitably functionalized derivatives of naphthalene-1,8-carboxymide. Six different dyads possessing either a different linker (a meta-phenylene or a para-phenylmethylene) or a corrole with different substituents at the 5 and 15 positions were prepared. A photophysical and spectroscopic characterization of the dyads and the reference models show that whereas upon selective excitation of the corrole component no photo-induced process occurs, excitation of the naphthalimide unit results in very efficient energy or electron transfer processes. The electron transfer contributes to the quenching process with a ratio between 0% and 85% depending on the nature of the corrole accepting unit. The processes are discussed in the frame of current theories. This is the first report of stable corrole-based dyads with interesting photo-activity at ambient temperature.

Solvent effect on the redox potential of quinone-semiquinone systems

Abstract Polarographic reduction of 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-phenanthrenequinone and 9,10-anthraquinone was studied in pyridine, acetone, hexamethylphosphoramide, dimethylformamide, dimethylacetamide, acetonitrile, dimethylsulfoxide and propylene carbonate. The variation of the E1/2-values proper for the first electron transfer step (measured against oxidation potential of ferrocene) with the properties of solvent is analyzed in terms of the donor-acceptor concept. Linear correlations of E1/2 vs. acceptor number are observed; the slopes of corresponding lines correlate with the spin densities at oxygen atoms of semiquinones.

Entropy of electrochemical formation of p-semiquinones—I. Effect of dipolar aprotic solvents

Abstract The entropy of formation, Δ S 0 r , of anion radicals for 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-anthraquinone and 5,12-tetracenequinone in a number of aprotic solvents has been determined in a nonisothermal cell from the temperature dependences of the reversible half wave potentials. Linear correlations between the Δ S 0 r values and the acceptor numbers of solvents have been observed. The same approach to the literature Δ S 0 r data for other organic molecules is discussed.

Synthesis and properties of directly linked corrole–ferrocene systems

Meso-substituted corroles bearing directly linked ferrocene unit have been synthesized for the first time. Among various methods studied, only the condensation of pentafluorophenyldipyrromethane with a formylferrocene led to this type of product. A triad containing corrole and porphyrin bridged with ferrocene has been obtained by a convergent approach. Bilanes were used as crucial substrates in the porphyrin-forming step. For the first time it was shown that H2O–MeOH–HCl conditions are suitable for preparation of various 10-(formylaryl)corroles via the direct condensation of aromatic dialdehydes with dipyrromethanes. Electrochemical studies of 10-ferrocenyl-5,15-bis(pentafluorophenyl)corrole support the possibility of intramolecular electron transfer from the corrole to the ferrocene system after the electrode oxidation of the ferrocene to a ferrocenium cation. We have studied the structure of 1-(corrolyl)-1′-(porphyrinyl)ferrocene by 1H NMR and UV-Vis. NMR spectra show that this compound has more conformational freedom than analogous, previously studied bis-porphyrinylferrocenes. Absorption spectra suggest the lack of strong electronic interaction between ferrocene and porphyrinoids for dyads and significant conjugation for the triad.

Electrochemical studies of ion pairs and triplets formed by alkali metal cations with 1,2-naphthosemiquinone and 1,2-naphthoquinone dianion

Abstract The properties of ion associates formed by alkali metal cations with 1,2-naphthosemiquinone radical anions and 1,2-naphthoquinone dianions have been polarographically studied in dimethylsulfoxide solutions. It was established that these radicals and dianions coexist in equilibria with corresponding ion pairs and triple ions. The values of association constants were calculated on the basis of the slightly modified method of De Ford and Hume. Some structural aspects of ion association in the systems investigated are discussed.

Solvent and ion pairing effects on the reaction entropy for the electroreduction of aromatic molecules

Abstract The reaction entropy, ΔSor, for the electroreduction of p-dicyanobenzene, anthracene and nitromesitylene has been measured in a number of solvents using a non-isothermal cell. The solvent effect on the values of ΔSor has been discussed in terms of the Born dielectric continuum model and the specific solvation given by the solvent parameters of Lewis acidity and basicity. A correlation between the solvent acceptor number and ΔSor values is observed in the case of p-dicyanobenzene radical anions with a localized charge at the cyano groups, whereas the dielectric approach is more important for anthracene radicals with a stronger charge delocalization when the specific solvation is much weaker. A two-parameter correlation with acceptor and donor numbers has been observed for the ΔSor values of nitromesitylene where association between the radical anions and electrolyte cations occurs. An increase in the ΔSor values for the reduction of o-naphthoquinone in dimethylsulphoxide with an increase in the association constant for a series of cations has been found.

Entropy of electrochemical formation ofp-semiquinones in dimethylformamide

Entropy of formation of anion radicals at the mercury electrode in dimethyl-formamide for 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-anthraquinone, and 5,12-tetracenequinone has been determined from the temperature dependences of the reversible half-wave potentials using a nonisothermal cell. The linear relationship between the entropy and the calculated spin density at the oxygen atom of semiquinones was established. Similarly the linear correlation of the literature reaction entropy for electrooxidation of a few heteroaromatic compounds versus the experimental spin density at a heteroatom (N, S or Se) from ESR measurements was also observed.ZusammenfassungDie Bildungsentropie von Anionenradikalen an der Quecksilberelektrode wurde in Dimethylformamid für 1,4-Benzochinon, 1,4-Naphthochinon, 9,10-Anthrachinon und 5,12-Tetracenchinon aus der Temperaturabhängigkeit der reversiblen Halbwellenpotentiale unter Benutzung einer nichtisothermen Zelle bestimmt. Es wurde eine lineare Abhängigkeit zwischen der Entropie und der berechneten Spindichte am Sauerstoffatom der Semichinone festgestellt. Eine ähnliche lineare Korrelation konnte für die Literaturdaten von Reaktionsentropien der Elektrooxidation einiger heteroaromatischer Verbindungen gegenüber den experimentellen Spindichten am Heteroatom (N, S, Se; ESR-Messungen) beobachtet werden.

Two parameter donor-acceptor approach to solvent effects on the electrode kinetics of cations

A two parameter approach to solvent variations in the electroreduction rate constants of cobalt complexes and europium cations is presented and discussed in terms of solvent—solute and solvent—solvent interactions.ZusammenfassungEs wird eine Zwei-Parameter-Annäherung der Lösungsmitteleinflüsse auf die Geschwindigkeitskonstanten der Elektroreduktion von Kobalt-Komplexen und Europium-Kationen präsentiert und auf der Basis von Lösungsmittel—gelöster Stoff- und Lösungsmittel—Lösungsmittel-Wechselwirkung diskutiert.

Solvent effect on kinetics of the chloride ion cleavage from anion radicals of 4-chlorobenzophenone

Abstract Formal potentials (expressed on the ferrocene scale) for the formation of 4-chlorobenzophenone anion radicals E RX/RX − o as well as for the Cl /Cl − couple increase with the solvent acceptor number but the second dependence is at least twice as strong. However, the rate constant for CCl bond cleavage in these radicals decreases with solvent acidity, indicating that solvation of the leaving anion does not determine the kinetics of cleavage. It is shown that solvent effects on the intrinsic rate constant are dominant and can be described by the Pekar factor, as proposed in the Saveant model.

A re-examination of temperature dependent reduction potentials of quinones from the point of view of the isokinetic relationship

Abstract Temperature dependent half-wave potentials for the reversible reduction of 1,4-benzoquinone, 1,4-naphthoquinone, 9,10-anthraquinone, and 5,12-tetracenequinone in N,N -dimethylacetamide, N,N -dimethylformamide, dimethylsulfoxide, propylene carbonate and acetonitrile are used as experimental examples for investigating the isokinetic relationship in heterogeneous electrochemical systems. Isokinetic behavior is found for each of the quinones on varying the solvent with the exception of acetonitrile. Based on results reported in previous papers of this series the isokinetic temperature is interpreted as being related to heat bath frequencies active in reactant solvent interactions and the significance of the absence of a matching frequency in the ir spectrum of acetonitrile is discussed. Thermodynamic arguments are applied to a relationship between the isokinetic half-wave potentials and gas phase electron affinities.