Singlet and triplet state quenching of aromatic cations by molecular oxygen

Abstract

Rate constants of fluorescence quenching by molecular oxygen, kSq, of 4 acridizinium ions and of 7 protonated heterocyclic compounds as well as protonated 6‐aminochrysene have been determined in acetonitrile at room temperature. They adopt values in the range between 3.0×108 M−1 s−1 and 2.9×1010 M−1 s−1. Singlet oxygen (1O2) efficiencies for the oxygen quenching of the singlet state, ϕSΔ, and the triplet state, ϕTΔ, could be determined for most of the compounds. The results indicate that fluorescence quenching can be described here as competition between energy transfer and a process involving the second excited triplet state, kSq shows at first approximation a correlation with the energy gap between the singlet state and the second excited triplet state. Quenching of the first excited triplet state by oxygen is ruled mainly by energy transfer. Rate constants, kTq, could be determined for 5 compounds and vary between 6.0×108 M−1 s−1 and 1.1 × 109 M−1 s−1.

N‐Alkoxyheterocycles As Irreversible Photooxidants

“…The Wigner spin rules state that oxygen should react with triplet excited states to give singlet oxygen, with a rate constant that is ca one ninth of the diffusion‐controlled limit . Actual rate constants for oxygen quenching often vary slightly from this value due to differences in the Franck‐Condon factors for energy transfer, determined mainly by reaction exothermicity . Thus, the fact that all of the rate constants are ca 10 9 m −1 s −1 is good evidence in favor of reaction of oxygen with an excited triplet state in each case.…”

Photosensitized Generation of Singlet Oxygen

“…The importance of CT interactions has been realized in the fluorescence quenching of molecules with high oxidation potential, which often results in particularly small rate constants k S Q , as for example in the investigations with series of cyanoanthracene derivatives by Schoof et al (54), and Kikuchi et al (55), Brauer and co‐workers (56,57), Wilkinson and co‐workers (17,19), and Kristiansen et al (58), with acridinium cations by Kikuchi et al (55), and with several heterocyclic aromatic cations by Wirp et al (59). For some acridinium cations, Kikuchi determined k S Q values which are even by two orders of magnitude smaller than k diff (55).…”

“…But significant progress has been made in the understanding of the different competing deactivation processes by Kikuchi and co‐workers (55,83), Brauer and co‐workers (56,57,59), and Wilkinson and co‐workers (17,19,22,23), Abdel‐Shafi and Worrall (84), and by Tanaka et al (87). Scheme 2 displays the IC processes, which are the elementary steps of the four most important quenching reactions of (Eqs.…”

The benzo[b]quinolizinium ion as a water-soluble platform for the fluorimetric detection of biologically relevant analytes

“…[77][78][79][80][81] In addition, a set of experimental 82 and computational 83 absorption data of quinolizinium derivatives was compiled. As a general trend, the benzo[b]quinolizinium (2a) absorbs and emits essentially in the same range as anthracene (1) (Figure 1) with an absorption maximum at 396 nm and an emission maximum at 407 nm in methanol, respectively.…”

“…As a general trend, the benzo[b]quinolizinium (2a) absorbs and emits essentially in the same range as anthracene (1) (Figure 1) with an absorption maximum at 396 nm and an emission maximum at 407 nm in methanol, respectively. 77,80 The emission lifetime of the parent compound 2a is 4.4 ns in CH 3 CN. 80 These data indicate that the benzo[b]quinolizinium ion has the ability to substitute an anthracene fluorophore while essentially maintaining the photophysical properties.…”