MARY and Optically Detected ESR Spectroscopy of Radical Cations ofcis-andtrans-Decalin in Nonpolar Solutions

Abstract

Optically detected ESR and magnetic field effect on recombination luminescence yield (MARY) spectroscopy of spin-correlated radical ion pairs were used to study cis-and trans-decalin radical cations in nonpolar solutions. The differences observed in cis-and trans-decalin spectra are demonstrated to agree with the existence of temperature-activated intramolecular dynamic transitions in trans-decalin radical cation. In diluted solutions with decalin added as acceptors, the MARY spectroscopy technique yields the spectra of the corresponding radical cations even at room temperature. Under these conditions, the fast limit of dynamic transitions in trans-decalin radical cation takes place. It is demonstrated that both cis-and trans-decalin radical cations take part in ion-molecular charge transfer to a neutral molecule, the rate constant being close to the diffusioncontrolled one.

Multimer Radical Ions and Electron/Hole Localization in Polyatomic Molecular Liquids: A Critical Review

“…Although the cycloalkane holes are paramagnetic species, these holes cannot be observed by magnetic resonance techniques, whether in neat cycloalkanes or in dilute solutions in high-IP liquids. Only recently has it been understood that rapid spin-lattice (T 1 ) relaxation in the high-symmetry cycloalkane radical cations precludes their detection using ODMR [70]. This relaxation is caused by dynamic averaging between the nearly degenerate ground and excited states of the radical cations; this degeneracy results from the Jahn-Teller distortion.…”

“…This relaxation is caused by dynamic averaging between the nearly degenerate ground and excited states of the radical cations; this degeneracy results from the Jahn-Teller distortion. For example, transdecalin cation isolated in room-temperature cyclohexane has T 1 < 7 ns [70]. Since it takes several tens of nanoseconds to flip the electron spin for detection, radical cations of these cycloalkanes cannot be detected by ODMR.…”

Radiation chemistry of organic liquids: Saturated hydrocarbons

“…At higher temperatures, the spectral diffusion caused by the rapid reaction (2) causes the ODMR spectrum to collapse to a single narrow line. For solvent holes in liquid cis-decalin, trans-decalin, and squalane, this narrow line was observed, albeit indirectly, using magnetic level-crossing and quantum beat spectroscopies [28,29,50,59]. In squalane, the residence time of the hole at the solvent molecule is relatively long, ca.…”

“…Charge transfer between c-C 6 D 12^+ and c-C 6 H 12 was observed in the gas phase, where it proceeds at » 1/3 of the collision rate [58]. Reaction (2) was observed for radical cations and molecules of cis-and trans-decalins in dilute cyclohexane solutions (where it proceeds with a diffusion-controlled rate) [50,59]. In low-temperature solid hydrocarbons (4-30 K), the hole hopping due to reaction (2) may be observed through the time evolution of the resonance lines in ODMR spectra [39,45]; the residence time of the self-trapped holes at a given molecule is 0.1-1 µs.…”

“…Indeed, both matrix-isolation EPR experiments and quantum-mechanical calculations indicate that the neutral cycloalkanes and their ground-state radical cations have rather different geometries [50,51,52]. For example, in cis-and trans-decalins the bridging C 9 -C 10 bond elongates from 0.153-0.156 nm in the neutral molecules to 0.19-0.21 nm in the 2 A 1 and 2 A g states of the radical cations, respectively [10,52].…”