Singlet oxygen photogeneration from X–O₂ van der Waals complexes: double spin-flip vs. charge-transfer mechanism

Singlet O2 Produced by Ultraviolet Dissociation of the β-ionone–O2 Complex

“…However, the individual moieties in eq undergo spin changes such that the closed shell organic chromophore is excited from the singlet ground state ( 1 M) to a low-lying triplet state ( 3 M), while molecular oxygen is excited from the triplet ground state to the lowest singlet state. This DSF transition was first noted in liquids, and the transition energy is approximately the sum of the chromophore triplet-state energy and the 1 O 2 energy …”

“…This DSF transition was first noted in liquids, 15 and the transition energy is approximately the sum of the chromophore triplet-state energy and the 1 O 2 energy. 16 Molecular beam experiments have previously detected 1 O 2 following excitation of the complex in the ultraviolet (UV) region using two different detection schemes. In one detection scheme, the complex is excited in the UV region, resulting in the production of 1 O 2 via eq 1.…”

“…In one detection scheme, the complex is excited in the UV region, resulting in the production of 1 O 2 via eq . Laser light at 225 nm then photodissociates the 1 O 2 , resulting in O ( 3 P) atom products, and the same laser wavelength ionizes the O ( 3 P) atoms via (2 + 1) resonance-enhanced multiphoton ionization (REMPI), resulting in O + that is detected via mass spectrometry. ,, These experiments have typically been performed with a single laser at 225 nm, although one experiment observed 1 O 2 production in a two-laser setup with an excitation wavelength as high as 260 nm for isoprene–O 2 . In the latter experiment, the yield of 1 O 2 peaked near 225 nm and production decreased with increasing excitation wavelength .…”

Investigation of O2–X (X = Pyrrole or Pyridine) Cluster Photodissociation Near 226 nm

“…Thus, any wavelength blue of 242 nm has sufficient energy to break the bond; however, photodissociation of O 2 is weak above 200 nm due to the low absorption cross section. Previous experiments with O 2 containing van der Waals clusters show significantly enhanced production of atomic oxygen following excitation near 226 nm. − These experiments investigated O 2 clustered with xenon, water, or various organic substances including unsubstituted hydrocarbons such as cyclohexane and benzene, − 1,3-butadiene, or isoprene , as well as substituted hydrocarbons such as methyl iodide. , Previous work has shown O 2 containing van der Waals clusters result in the production of O 2 (a 1 Δ g ). − Furthermore, it is known that production of O 2 (a 1 Δ g ), following excitation by a photosensitizer, results in DNA damage inside of living cells . In this paper, we are interested in the dissociation channels of O 2 clustered with pyrrole and pyridine.…”

“…More recent studies involving O 2 clustered with isoprene or with 1,3-butadiene, CD 3 I, benzene, or water concluded that channel C5 is due to excitation resulting in the formation of O 2 (a 1 Δ g ) along with the organic fragment in the lowest triplet state. The excited O 2 (a 1 Δ g ) subsequently absorbs a second photon and dissociates. , Baklanov et al’s work showed an increased propensity for the fast C5 channel to produce atomic oxygen in the excited O ( 3 P 0 ) state relative to either of the low energy O ( 3 P 1 ) or O ( 3 P 2 ) states of atomic oxygen .…”