Anion resonances and above-threshold dynamics of coenzyme Q₀

Abstract

The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-pro t purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Temporary radical anions (resonances) of isolated co-enzyme Q 0 (CQ 0 ) and their associated above-threshold dynamics have been studied using frequency-, angle-, and time-resolved photoelectron imaging (FAT-PI). Experimental energetics and dynamics are supported with ab initio calculations. All results support that CQ 0 exhibits similar resonances and energetics compared with the smaller para-benzoquinone subunit, which is commonly considered as a prototype electrophore for larger biological para-quinone species. However, the abovethreshold dynamics in CQ 0 relative to para-benzoquinone show significantly enhanced prompt detachment compared with internal conversion, particularly around the photoexcitation energy of 3.10 eV. The change in dynamics can be attributed to a combination of an increase in the shape character of the optically-accessible resonance at this energy, a decrease in the autodetachment lifetime due to the higher density of states in the neutral, and a decrease in the probability that the wavepacket formed in the FranckCondon window can access the local conical intersection in CQ 0 over the timescale of autodetachment. Overall, this study serves as a clear example in understanding the trends in spectroscopy and dynamics in relating a simple prototypical para-quinone electrophore to a more complex biochemical species.

Internal conversion outcompetes autodetachment from resonances in the deprotonated tetracene anion continuum

“…Our earlier combined experimental and computational studies on π* resonances of para-quinones support that XMCQDPT with a sufficiently large reference active space and sufficiently compact basis provides a reasonable account of resonance vertical photoexcitation energies. 26,27,57 Results and Discussion Photoelectron spectra Fig. 2 summarises all PE spectra as a waterfall plot.…”

“…The mechanism through which above-threshold population is funnelled to the ground electronic state is internal conversion via conical intersections that result from strong non-adiabatic electronic state couplings. [24][25][26][27][28] …”

“…The mechanism through which above-threshold population is funnelled to the ground electronic state is internal conversion via conical intersections that result from strong non-adiabatic electronic state couplings. [24][25][26][27][28] Complete internal conversion to the ground electronic state can be assisted by intermediate states that are close in energy, or by a ladder of intermediate states. In particular, bound electronic states of the anion have been shown to be important intermediates.…”

“…22 Although spontaneous autodetachment from a resonance is typically very fast (tens to hundreds of femtoseconds), non-adiabatic internal conversion can compete and even dominate. [24][25][26][27][28] Indeed, many electron impact studies on conjugated molecules have observed efficient formation of long-lived anions despite the incident electron energies and molecular configurations incompatible with an electric dipole-mediated capture mechanism. 22,29 As a specific example, mass spectrometry measurements on tetracene and pentacene have shown the formation of long-lived anions with lifetimes of ~10 ms following capture of electrons with up to ~3 eV of kinetic energy.…”

Charged Particle Imaging of the Deprotonated Octatrienoic Acid Anion: Evidence for a Photoinduced Cyclization Reaction

“…But, it is also well-established that * resonances can often complicate the photoelectron spectroscopy of bright chromophore anions, particularly in polyaromatic and highly conjugated systems, where photoexcitation to resonances can be much more probable than direct photodetachment. [14][15][16][17] The dynamics of such resonances can have striking effects on the measured photoelectron spectra, since ultrafast excited state nuclear motion can compete with autodetachment. 18,19 These effects can take the form of changing Franck-Condon factors, internal conversion dynamics, or dissociation dynamics leading to an anionic fragment from which an electron is subsequently photodetached.…”