Formation of p-terphenyl excited states in the ionic liquid methyltributylammonium bis[(trifluoromethyl)sulfonyl]imide: pulse radiolysis study

Abstract

Solutions of 80 mM benzophenone (BP) and up to 14 mM p-terphenyl (TP) in the ionic liquid methyltributylammonium bis[(trifluoromethyl)sulfonyl]imide (R 4 NNTf 2 ) have been investigated by nanosecond pulse radiolysis. The resulting transient absorption spectra of pulse-irradiated argon saturated solutions correspond to the formation of several intermediates derived from BP and TP: benzophenone radical anion [(C 6 H 5 ) 2 CO] •-(BP •-) converted after *20 ls into ketyl radicals (C 6 H 5 ) 2 C • OH (BP • H), a hydrogen adduct to the phenyl ring of benzophenone C 6 H 5 COC 6 H 6 • , p-terphenyl triplet excited state 3 TP*, and traces of TP radical ions. 3 TP* was formed in two steps, the first immediately during the pulse and the second in pseudo-first order process with a second order reaction rate constant calculated from TP concentration dependence: k = *2 9 10 8 dm 3 mol -1 s -1 .

Pulse radiolysis studies of intermediates derived from p‐terphenyl in the oxygenated methyltributylammonium bis[(trifluoromethyl)sulfonyl]imide ionic liquid

“…Pulse radiolysis coupled with the time‐resolved UV‐vis spectrophotometry was performed using the INCT LAE 10 linear accelerator with typical electron pulses lengths of 7‐10 ns. A detailed description of the computer‐controlled experimental setup has been given elsewhere . The system consists of the 150‐W “quiet” xenon lamp (Hamamatsu E7536) with a suitable housing and a power supply, the Oriel MSH 301 monochromator with two switchable outputs (one for a R955 photomultiplier and the second one for the ANDOR ICCD camera—intensified charge coupled device) and the LeCroy WaveRunner 6051A oscilloscope with an internal memory of 16 Mb.…”

“…BP was used as a primary scavenger of electrons ( e presolv − / e solv − ) and excited states of the IL components, that is, ([MeBu 3 N] + )* and ([NTf 2 ] − )*. However, it was previously found that the energy transfer from the excited states of this IL is of minor importance …”

“…Pulse‐irradiation of a neat [MeBu 3 N][NTf 2 ] IL leads besides excitation also to ionization of its components. The primary products of radiolysis of [MeBu 3 N][NTf 2 ] IL: presolvated electrons ( e presolv − ), solvated electrons ( e solv − ), electron‐deficient centers (IL ⊕ ), radical anions (IL Ө ), and excited states (IL*) located on both the anions and cations of IL have already been reported elsewhere . Recently, some of the primary intermediates, that is, e presolv − / e solv − and IL ⊕ resulting from the radiolysis of a neat [MeBu 3 N][NTf 2 ] IL were also probed by using TP .…”

“…However, it was previously found that the energy transfer from the excited states of this IL is of minor importance. 34 Pulse-irradiation of a neat [MeBu 3 N][NTf 2 ] IL leads besides excitation also to ionization of its components. The primary products of radiolysis of [MeBu 3 N][NTf 2 ] IL: presolvated electrons (e presolv − ), solvated electrons (e solv − ), electron-deficient centers (IL ⊕ ), radical anions (IL Ө ), and excited states (IL*) located on both the anions and cations of IL have already been reported elsewhere.…”

“…21 Direct observation of the remaining primary products derived from [MeBu 3 N][NTf 2 ] was not possible. Therefore, TP was selected as a probe since the transients derived from TP such as radical anions (TP •− ), radical cations (TP •+ ), and excited states (singlet excited states-1 TP* and triplet excited states-3 TP*) absorb in the spectral region available and convenient for time-resolved measurements using UV-vis spectrophotometry [34][35][36][37][38][39][40] (see Table 1). Moreover, TEA was used as an electron donor and an effective scavenger of IL ⊕ , 3 TP*, and TP •+ .…”