Quenching of the singlet and triplet state of benzene by halogenated alkanes in the vapor phase

Abstract

. 60, 1767 (1982).The second order rateconstants (k,) for the quenching of the singlet state of benzene by several halogenated alkanes (viz. CH,Br2, CCI,, CH3CC13, CHCI,, CHF,, CH,CI, CH3F, CH2F2, CH2C12, CFCI,, CF2CI2, CF,CI, CF,) in the vapor phase have been measured. For CCl,, CHCI,, CH2C12, and CH,CI, which were previously studied by Das Gupta and Phillips, there is satisfactory agreement between the k, values obtained in the separate investigations. The linear dependence of the electron affinity of quencher with the corresponding quenching rate constants supports an exciplex mechanism in accordance with Klein's model. Charge transfer occurs from benzene to halogenated alkane and is greater for the chloro alkanes than for mixed fluoro-chloro alkanes. In the case of the triplet state of benzene, whose behaviour was monitored using the sensitized emission of biacetyl technique, quenching effects were at best one order of magnitude smaller and probably involve more than one bimolecular process.

Quenching of the fluorescence of substituted benzenes by halomethanes

“…In the case of benzene and a large number of halocarbons it Finally, if full electron-transfer from excited aromatic to has been shown that In k, does indeed vary linearly with EAA, quencher occurs, the maximum slope should be l/RT -39 all the other terms of eq. [6] being constant. In the present case eV-I.…”

“…The charge transfer exciplex model of quenching is based on ketones (4) [5] In k, = ---+ In k2 RT [6] In k, x l -( l P~ -EAA -E s~ -C -P)I/RT possible to test eq. [6] by plotting In k, vs. lPD; the results of this plot are shown in Fig.…”

“…If the resulting plot of In k , vs. EA or IP is linear it is considered likely that a C T exciplex is responsible for quenching. Recently we reported (6) on the quenching of benzene fluorescence by a number of halocarbons in the gas phase. In that study a good Klein correlation between k,, and EA of the halocarbons was established, thus suggesting a CT exciplex and charge transfer from benzene to halocarbon.…”

Quenching of the singlet and triplet state of benzene in condensed phase

“…It has also been shown that polar solvents increase this quenching (22,23). In a previous publication we reported on the fluorescence quenching of benzene vapour by a number of halocarbons (6). We report here on the effect of solvent polarity on this reaction in liquid phase and on the rates of quenching by CCl,, CH,CN, CHCl,, and CH3CCl, in solid phase.…”

“…Some exciplexes exhibit fluorescence which is characterized by a red-shift with respect to the uncomplexed excited monomeric state, a lack of vibronic structure, and different decay characteristics. Nonemissive exciplexes have also been shown to exist (2)(3)(4)(5)(6). In such cases, indirect evidence is obtained for the intermediacy of exciplexes.…”