RESUMEN
The use of the Sm2+ luminescence properties in numerous applications appeals for a better understanding of its electronic structure. This work compares luminescence data and crystal field parameters from 31 Sm2+-containing compounds to assess the effects of the crystal field on its energy levels. In particular, the relationship between the 5D0-7F0 and 5D0-7F1 transition energies is analyzed and compared with previously published data for the isoelectronic Eu3+. It appears that for Sm2+, in contrast to Eu3+, the energy of the 5D0 state cannot be considered to be constant and implies the involvement of an extra state (presumably the 4f55d1 level) in the mixing of the 4f6 states. On the other side, the total crystal field strength is correlated to the splitting of the 7F1 states for both Sm2+ and Eu3+ in lower symmetry environments. The plot of the 5D0-7F0 energy as a function of the 7F1 splitting clearly evidences the mixing of the 4f6 state with the environment-sensitive 4f55d1 state for Sm2+, which is finally confirmed by the discrepancy of the ratio between the 5D1 and 7F1 splittings from its theoretical value in the absence of any mixing with the 4f55d1 state.
RESUMEN
One-pot synthesis of organic-inorganic hybrid materials under light requires specific photoinitiating systems which are able to release several different initiating species after light absorption. In this paper, the reaction mechanism of a photocyclic three-component initiating system based on isopropylthioxanthone as photoinitiator and an iodonium salt and a thiol as co-initiators was studied. It is shown that this system enables simultaneous release of both radicals and protons which are able to initiate a free radical photopolymerization and the hydrolysis-condensation of a sol-gel network, respectively. Time-resolved investigations by laser flash photolysis show that the initiating species are produced within two concomitant cyclic reaction mechanisms depending on the relative quantities of the co-initiators. Protons resulting from the secondary dark reaction of the photocyclic systems are detected at the microsecond scale by means of a proton-sensitive molecular probe, and corresponding quantum yields are measured. Finally, synthesis of organic, inorganic, and hybrid materials under LED light at 395 nm is evaluated with respect to the mechanistic considerations demonstrating the dual initiating character of the system.
RESUMEN
Photocatalysis reactions using [Ru(II) (bpy)3 ](2+) were studied on the example of visible-light-sensitized reversible addition-fragmentation chain transfer (RAFT) polymerization. Although both photoinduced electron- and energy-transfer mechanisms are able to describe this interaction, no definitive experimental proof has been presented so far. This paper investigates the actual mechanism governing this reaction. A set of RAFT agents was selected, their redox potentials measured by cyclic voltammetry, and relaxed triplet energies calculated by quantum mechanics. Gibbs free-energy values were calculated for both electron- and energy-transfer mechanisms. Quenching rate constants were determined by laser flash photolysis. The results undoubtedly evidence the involvement of a photoinduced energy-transfer reaction. Controlled photopolymerization experiments are discussed in the light of the primary photochemical process and photodissociation ability of RAFT agent triplet states.
RESUMEN
The combination of a dye which absorbs the photon, an electron acceptor and an electron donor leading to energy conversion through electron transfer, was the basis of the so called three-component systems. In this paper, an experimental work combining Rose bengal dye with a triazine derivative as electron acceptor and ethyl 4-(dimethylamino)benzoate as electron donor, will underline the benefit of the photocyclic behavior of three-component systems leading to the dye regeneration. A thermodynamic approach of the photocycle is presented, followed by a mechanistic and computational study of ideal photocycles, in order to outline the specific kinetics occuring in so called photocatalytic systems. The simple kinetic model used is enough to outline the benefit of the cyclic system and to give the basic requirements in term of chemical combination needed to be fulfilled in order to obtain a photocatalytic behavior.
