Lajos Fodor

Synthesis, Photochemistry, and Photophysics of Butadiene Derivatives: Influence of the Methyl Group on the Molecular Structure and Photoinduced Behavior

Novel butadiene derivatives display diverse photochemistry and photophysics. Excitation of 2-methyl-1-(o-vinylphenyl)-4-phenylbutadiene leads to the dihydronaphthalene derivative, whereas photolysis of the corresponding model o-methyl analogue results in the formation of the naphthalene-like derivative, deviating from the nonmethylated analogue of the prior starting compound and producing benzobi- and -tricyclic compounds. The effect of the methyl substituents is even more dramatic in the case of the dibutadienes. The parent unsubstituted compound undergoes photoinduced intramolecular cycloaddition giving benzobicyclo[3.2.1]octadiene, whereas the photochemical reaction of the corresponding dimethylated derivative shows only geometrical isomerization due to the steric effect of the substituents. Methyl groups on the butadiene backbones reduce the extent of conjugation, causing a blue-shift of the characteristic absorption band. The fluorescence efficiency is dramatically decreased, as a consequence of nonplanarity and reduced rigidity of the molecules due to the crowding by the methyl and phenyl groups together. Four molecules of very similar structures show dramatically different photoinduced behavior, revealing how changes of the nature and position of the substituents are valuable in understanding the photophysics and photochemistry of these types of compounds.

Enhancement of magnetic field effect in Ru(bpy)32+/MV2+ system by Ru(bpy)32+-Ag+ exciplex formation

Abstract The influence of ionic strength variation and of exciplex formation between silver ions and triplet excited RuL 3 2+ (L=bipyridine, phenanthroline) on the photo electron transfer kinetics of the complex with methylviologen and the magnetic field dependence of free radical formation efficiency has been studied by laser flash spectroscopy. The magnetic field effect consisting in a decrease of the efficiency of cage escape η ce in the Ru(bpy) 3 2+ /MV 2+ system is enhanced by 40% when exciplex formation between Ag + ions and triplet excited RuL 3 2+ complexes takes place. The relevant kinetic parameters have been determined by magnetokinetic model calculations.

Ligand dependence of magnetic spin effects on photooxidation of (Ru(bpy)3 n(CN)2n) ( 2 2n) type complexes

Photoinduced electron transfer reaction from the series of [Ru(bpy)(3� n )(CN)2n ] (2�� 2n ) complexes (n� /0, 1, 2) to methylviologen has been investigated using external magnetic field modulation in order to obtain relevant kinetic parameters for spin relaxation, backward electron transfer and cage escape of the geminate radical pair. The replacement of one bpy by two cyanide ligands results in an increase of the quenching rate constant and a decrease of the cage escape efficiency. The latter is decreased in a magnetic field

Investigation of Hydrogen Production from Alkaline Sulfide Solution with Nanosized CdS/ZnS-PdS Photocatalyst of Various Compositions

Hydrogen sulfide is highly toxic to humans and harmful to the environment. On the other hand, H₂S is produced in large quantities in some industrial processes like the refinery of crude oil and the sweetening of natural gas. Nowadays, H₂S is usually burned to sulfur and water in the Claussprocess wasting the energy of hydrogen stored in H₂S. Progress in the area of photocatalysis results in considerable development of the heterogeneous photocatalytic conversion of hydrogen sulfide into hydrogen gas. In this work, photocatalytic hydrogen production from alkaline sulfide solutions was investigated, utilizing various ZnS/CdS composites modified with PdS as cocatalyst. The highest photocatalytic activity was found at 1:1 molar ratio of CdS and ZnS. At this catalyst content the optimal PdS-loading was investigated in the range of 0-0.4% (n/n); the 0.05-0.10% (n/n) PdS content proved to be most efficient. The catalyst consisted of the agglomerates of 80-150 nm size particles. During long time illuminations (10 days) the size of the agglomerates increased, but the diameter of the individual particles and the photocatalytic activity did not noticeably change. The dependence of the rate of hydrogen production on the concentration of sulfide, sulfite, and thiosulfate ions was also studied. An increase of the amount of reactants resulted in an enhancement of the reaction rate, while the presence of thiosulfate ions lowered the catalytic activity. One of the possible reasons of this effect is the side reaction of thiosulfate ions by the conduction band electrons.