Effect of Solvent on the O2(aΔg) → O2(b1Σg+) Absorption Spectrum:  Demonstrating the Importance of Equilibrium vs Nonequilibrium Solvation

Dam, Niels Arne; Keszthelyi, Tamás; Andersen, Lars Klembt; Mikkelsen, Kurt V.; Ogilby, Peter R.

doi:10.1021/jp0200876

Cited by 18 publications

(46 citation statements)

References 40 publications

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“…1). 38,39 Although this approach complements the O 2 (a 1 D g ) -O 2 (X 3 S À g ) phosphorescence method nicely, and can provide unique mechanistic information, [40][41][42] it suffers from the general rule that absorption techniques are not as sensitive as luminescence techniques. Thus, even though a singlet oxygen absorption microscope has been developed, 43 for example, I will focus in this review on techniques for direct singlet oxygen detection that are based on the O 2 (a 1 D g ) -O 2 (X 3 S À g ) phosphorescent transition.…”

Section: The Photosensitized Production Of Singlet Oxygenmentioning

confidence: 99%

Singlet oxygen: there is indeed something new under the sun

2010

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Singlet oxygen, O(2)(a(1)Delta(g)), the lowest excited electronic state of molecular oxygen, has been known to the scientific community for approximately 80 years. It has a characteristic chemistry that sets it apart from the triplet ground state of molecular oxygen, O(2)(X(3)Sigma), and is important in fields that range from atmospheric chemistry and materials science to biology and medicine. For such a "mature citizen", singlet oxygen nevertheless remains at the cutting-edge of modern science. In this critical review, recent work on singlet oxygen is summarized, focusing primarily on systems that involve light. It is clear that there is indeed still something new under the sun (243 references).

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Section: The Photosensitized Production Of Singlet Oxygenmentioning

confidence: 99%

Singlet oxygen: there is indeed something new under the sun

2010

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“…Again, the data are most extensive for the a → X transition, , but appreciable information about the other two transitions has become available from absorption experiments (Figure a). ,,, It is reasonable to compare absolute spectral features independently obtained from absorption and emission experiments because the Stokes shifts for these transitions are small (i.e., <3 cm –1 ) …”

Section: Solvent-mediated Spectral Changesmentioning

confidence: 99%

Singlet Oxygen Photophysics in Liquid Solvents: Converging on a Unified Picture

et al. 2017

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Singlet oxygen, O(aΔ), the lowest excited electronic state of molecular oxygen, is an omnipresent part of life on earth. It is readily formed through a variety of chemical and photochemical processes, and its unique reactions are important not just as a tool in chemical syntheses but also in processes that range from polymer degradation to signaling in biological cells. For these reasons, O(aΔ) has been the subject of intense activity in a broad distribution of scientific fields for the past ∼50 years. The characteristic reactions of O(aΔ) kinetically compete with processes that deactivate this excited state to the ground state of oxygen, O(XΣ). Moreover, O(aΔ) is ideally monitored using one of these deactivation channels: O(aΔ) → O(XΣ) phosphorescence at 1270 nm. Thus, there is ample justification to study and control these competing processes, including those mediated by solvents, and the chemistry community has likewise actively tackled this issue. In themselves, the solvent-mediated radiative and nonradiative transitions between the three lowest-lying electronic states of oxygen [O(XΣ), O(aΔ), and O(bΣ)] are relevant to issues at the core of modern chemistry. In the isolated oxygen molecule, these transitions are forbidden by quantum-mechanical selection rules. However, solvent molecules perturb oxygen in such a way as to make these transitions more probable. Most interestingly, the effect of a series of solvents on the O(XΣ)-O(bΣ) transition, for example, can be totally different from the effect of the same series of solvents on the O(XΣ)-O(aΔ) transition. Moreover, a given solvent that appreciably increases the probability of a radiative transition generally does not provide a correspondingly viable pathway for nonradiative energy loss, and vice versa. The ∼50 years of experimental work leading to these conclusions were not easy; spectroscopically monitoring such weak and low-energy transitions in time-resolved experiments is challenging. Consequently, results obtained from different laboratories often were not consistent. In turn, attempts to interpret molecular events were often simplistic and/or misguided. However, over the recent past, increasingly accurate experiments have converged on a base of credible data, finally forming a consistent picture of this system that is resonant with theoretical models. The concepts involved encompass a large fraction of chemistry's fundamental lexicon, e.g., spin-orbit coupling, state mixing, quantum tunneling, electronic-to-vibrational energy transfer, activation barriers, collision complexes, and charge-transfer interactions. In this Account, we provide an explanatory overview of the ways in which a given solvent will perturb the radiative and nonradiative transitions between the O(XΣ), O(aΔ), and O(bΣ) states.

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“…Monitoring the effect of solvent on the O 2 (b 1 Σ g + ) → O 2 (a 1 Δ g ) emission spectrum provided additional experimental challenges, but this was accomplished shortly thereafter (67,74,104). Finally, and most challenging of all, were experiments to record O 2 (a 1 Δ g ) → O 2 (b 1 Σ g + ) absorption spectra (67,74,105–107). The data obtained portray a consistent picture.…”

Section: Perturbed and Solvated Oxygenmentioning

confidence: 99%

“…Nevertheless, the perturbing effect of M on O 2 , and conversely O 2 on M, can be quite pronounced. Thus, for example, even though M‐induced spectral shifts in the O 2 (a 1 Δ g )‐O 2 (X 3 Σ g − ) and O 2 (b 1 Σ g + )‐O 2 (a 1 Δ g ) transitions are generally quite small (54,55,81,104,106,108), the effect of M on O 2 (a 1 Δ g )‐O 2 (X 3 Σ g − ) and O 2 (b 1 Σ g + )‐O 2 (a 1 Δ g ) transitions probabilities can be very large (81,107,108,115–117). Of course, this is a manifestation of the fact that these transitions are forbidden in the isolated O 2 molecule.…”

Section: Chemical Reactionsmentioning

confidence: 99%