Quenching of electronically excited states by molecular oxygen in fluid solution

Abstract

Absrract: Rate constants, e, for quenching by oxygen of the triplet states of anthracene, biphenyl and naphthalene derivatives in acetonitrile and the efficiencies of formation thereby of singlet oxygen, f : , are discussed in the light of the new values obtained for biphenyl derivatives. In the case of anthracene derivatives little v 'ation in 9 or f i is observed but for biphenyl and naphthalene derivatives the rate constants decrease as their oxid tion potential rises whilst fT aries in the opposite direction. In the case of biphenyl derivatives fA rises from 0.3 1 to 0.84 as%:2 decreases from 12.5 to 0.88 x 109 dm3 mol-1 s-1 on going from 4,4'dimethoxybiphenyl to 4-cyanobiphenyl. The mechanism of quenching via singlet and triplet channels is discussed and the importance of the energy of the charge transfer state involving electron transfer to oxygen, Elative to the energy of the locally excited triplet state is established as important in determining kr2 and f i . These results indicate that charge transfer assisted quenching occurs via both singlet and triplet complexes with only partial (up to 13.5% ) charge transfer character.

Triplet state dynamics on isolated conjugated polymer chains

“…The rate constants for quenching the triplet states of the polymers by oxygen are close to those observed with oxygen quenching of the triplet states of many small organic molecules [60], and are in the range 0:5-2:5 Â 10 9 M À1 s À1 , approximately 1/9th the diffusion controlled limit in benzene solution (10 10 M À1 s À1 [61]). This factor of 1/ 9th arises from spin multiplicity considerations when a ground state molecule and singlet oxygen are formed from two triplet states [60,62,63], and results from the fact that while interaction of the triplet state of the substrate and oxygen ( 3 R À g ) will produce complexes with quintet, triplet and singlet multiplicity, these are formed reversibly and only the singlet complex leads to quenching (i.e., 1 in every 9 collisions is effective).…”

Photoacoustic Measurements of Porphyrin Triplet-State Quantum Yields and Singlet-Oxygen Efficiencies

“…(14) ± (16)], [44] the rate constant of the quenching by oxygen (k q k TD k TS ) can be obtained from the lifetimes of the triplet in N 2 and airsaturated solutions from Equation (17) Following the pioneering work of Porter, [45] it is believed that when k q % 1 / 9 k diff the quenching of triplet states by molecular oxygen follows an energy-transfer mechanism. In toluene at room temperature 1 / 9 k diff 3.4 Â 10 9 m À1 s…”

Photophysical characterization of the plant growth regulator 2-(1-naphthyl) acetamide

“…Quenching of 1 NAD* and 3 NAD* by molecular oxygen Molecular oxygen is an important quencher of both singlet and triplet excited states of molecules [10,11,49,50], producing photophysical consequences such as fluorescence and triplet quenching, enhanced intersystem crossing and production of singlet oxygen, 1 O 2 ( 1 g ). Hence, we have determined the rate constants for quenching of 1 NAD* by molecular oxygen, k O 2 S , in the various solvents in oxygenated, aerated and de-aerated solutions, through a Stern-Volmer plot of the fluorescence intensity ratios for aerated and de-aerated solutions vs oxygen concentration.…”