Reactivity and Efficiency of Singlet- and Triplet-Excited States in Intermolecular Hydrogen Abstraction Reactions

Abstract

The rate constants for quenching of the singlet- and triplet-excited state of acetone and a cyclic azoalkane by the hydrogen donors tributyltin hydride, 1,4-cyclohexadiene, and 2-propanol have been determined by time-resolved spectroscopy. It is concluded, in variance with previous studies, that singlet-excited states are significantly more reactive than triplet-excited states and that the reactivity difference between the two states of different spin multiplicity increases (i) with decreasing reactivity of the hydrogen donor and (ii) with increasing singlet−triplet energy gap of the excited state. This result is corroborated by semiempirical calculations. The relative efficiency for photoreduction by tributyltin hydride, which was determined by monitoring the formation of tributyltin radicals upon flash photolysis, was found to be four times lower for singlet-excited acetone than for the triplet state. The discrepancy between higher reactivity but lower efficiency in the intermolecular interaction of n,π*-excited singlet states with hydrogen donors is attributed to efficient radiationless deactivation, which has been predicted by correlation diagrams as a viable pathway for singlet-excited states.

Functionalization of polymeric surfaces by simple photoactivation of CH bonds

“…[29][30][31][32][33][34][35][36] have also been reported. 36 The results showed that formaldehyde, acetone, and cyclohexanone have a high grafting efficiency, especially acetone which gives the highest grafting efficiency.…”

Photo-induced inactivation of viruses: adsorption of methylene blue, thionine, and thiopyronine on Qbeta bacteriophage.

“…Growth A Continuum PY61-10 Nd-YAG laser system was used for excitation at 532 nm (=0.5 mJ per 30-ps pulse) and a Hamamatsu streak scope C4334 system with Hamamatsu software was used for time-resolved fluorescence detection and data acquisition. This technique allows collection of fluorescence lifetimes and real-time kinetic quenching data in the fluorescence time regime relevant for the examination of the dyes (0.1-10 ns) (16 (Fig. 1) but show higher singlet energies and lower reduction potentials (Table 1).…”

Direct ab initio MD study on the hydrogen abstraction reaction of triplet state acetone from methanol molecule

“…The results of direct ab-initio MD calculations of the complex with zero-point energy 8 (ZPE) on the ground state S 0 state are illustrated in Figure 3. The ZPE dynamics calculation showed that the potential energy oscillates periodically as a function of time, and the structural conformation of the complex changes markedly over time during the simulation.…”

“…Acetone, one of the simplest C=O carbonyl compounds, also causes an intermolecular hydrogen abstraction reaction. Nau et al [8] measured rate constants for quenching of excited state acetone by hydrogen donor tributyltin hydride and 2-pripanol using time-resolved spectroscopy. They showed that both singlet-and triplet excited states can abstract a hydrogen atom of the donor molecules.…”

“…Recently, the reaction via singlet excited S 1 state has been also observed experimentally. Nau et al [8] showed that the S 1 acetone has a higher reactivity but lower efficiency than the reaction via T 1 state. This is attributed to an efficient radiationless deactivation on the S 1 state.…”