Effect of Solvent on the O₂(a¹Δ_g) → O₂(b¹Σ_g⁺) Absorption Coefficient

Abstract

Radiative transitions between the three lowest-lying electronic states of molecular oxygen have long provided a model to study how collision-dependent perturbations influence forbidden processes. In an isolated oxygen molecule, transitions between the O2(X(3)Σg(-)), O2(a(1)Δg), and O2(b(1)Σg(+)) states are forbidden as electric-dipole processes. For oxygen dissolved in organic solvents, the probabilities of radiative transitions between these states increase appreciably. Attempts to interpret solvent-dependent changes in the radiative rate constants have principally relied on O2(b(1)Σg(+)) and O2(a(1)Δg) emission experiments. However, the dominant nonradiative deactivation channels of O2(b(1)Σg(+)) make it difficult to quantify solvent effects on the O2(b(1)Σg(+)) → O2(a(1)Δg) radiative process. Thus, an appreciable amount of important information has heretofore not been available. In the present study, we examined the effect of 17 common organic solvents on the O2(a(1)Δg) → O2(b(1)Σg(+)) absorption transition at ∼5200 cm(-1) (i.e., ∼1925 nm). The solvent-dependent absorption coefficients at the band maximum, εmax, range from 5 to 50 M(-1) cm(-1) and correlate reasonably well with the solvent refractive index; εmax is largest in solvents with the largest refractive index. This observation is consistent with a model in which oxygen is perturbed to a greater extent by solvents with a large electronic polarizability. Through the Strickler-Berg equation, we also used these absorption data to obtain the radiative rate constant for the O2(b(1)Σg(+)) → O2(a(1)Δg) transition, and the results are consistent with a model in which the O2(a(1)Δg) → O2(X(3)Σg(-)) transition is said to steal intensity from the O2(b(1)Σg(+)) → O2(a(1)Δg) transition.

Direct 1O2 optical excitation: A tool for redox biology

“…If it is the case that 1 O 2 (b) is the generated species, it undergoes very fast conversion to 1 O 2 (as mentioned in Section 2 [37]), which is the biologically relevant molecule. Monomol absorption bands are very weak: the corresponding molar absorption coefficients are ~10 −3 – 10 −4  M −1  cm −1 [45], [46], [105], [106], [107] or even lower. These absolute values are 10 7 – 10 9 smaller than typical absorption coefficients for PDT PSs (but notice that PSs are commonly employed at 10 −5 – 10 −6  M final concentration).…”

“…The excitation energy is lost to the medium first as vibrational energy, which finally decays to heat. The energy coupling among 1 O 2 and apolar non-hydrogenated solvents is much less efficient, and its lifetime is consequently prolonged, reaching very high values (milliseconds) [44], [45], [46]. Finally, 1 O 2 can engage in chemical reactions with a host of substrates.…”

Spectral dependence of the efficiency of direct optical excitation of molecular oxygen in tetrachloromethane

“…Many studies [16][17][18][19][20][21][22][23][24], both theoretical and experimental, have been devoted to the influence of molecular environment of oxygen in gas or condensed matter on the parameters and properties of transitions from the singlet oxygen states to the ground state. The theoretical estimates [16][17][18] of the possibility of increasing the radiative probability of transitions from the singlet states of an oxygen molecule to the ground state under the effect of molecular environment have been convincingly confirmed by experiments [19][20][21][22][23][24].…”

Фотолюминесценция Политетрафторэтилена В Ближней Инфракрасной Области Спектра

“…При этом величина поглощения кислорода или, точнее, комплексов кислорода с внешним окружением заметно возрастает, как и интенсивность фотолюминесценции этих комплексов. Изучению влияния внешнего молекулярного окружения кислорода в газе или в конденсированной среде на параметры и свойства переходов из синглетных состояний кислорода в основное состояние посвящено большое количество как теоретических, так и экспериментальных работ [24][25][26][27][28][29][30][31][32]. При этом выполненные теоретические оценки [16][17][18] о возможности повышения излучательной вероятности переходов из синглетных состояний молекулы кислорода в основное под воздействием внешнего окружения получили убедительное экспериментальное подтверждение [27][28][29][30][31][32].…”

“…Изучению влияния внешнего молекулярного окружения кислорода в газе или в конденсированной среде на параметры и свойства переходов из синглетных состояний кислорода в основное состояние посвящено большое количество как теоретических, так и экспериментальных работ [24][25][26][27][28][29][30][31][32]. При этом выполненные теоретические оценки [16][17][18] о возможности повышения излучательной вероятности переходов из синглетных состояний молекулы кислорода в основное под воздействием внешнего окружения получили убедительное экспериментальное подтверждение [27][28][29][30][31][32]. Образование этих комплексов влияет и на формирование спектрального профиля поглощения, индуцированного столкновениями с внешним окружением [33].…”