Phosphorescence and optical detection of magnetic resonance (ODMR) studies of poly(methylpropylsilylene)

Determination of Stability and Degradation in Polysilanes by an Electronic Mechanism

Polysilanes are potential candidates for active materials in light emitting diodes because of possible emission in the near-ultraviolet to blue region. Unfortunately, they degrade rapidly upon exposure to light because of scission of sigma bonds. Relative stability of four polysilanes, for example, poly(di-n-butylsilane) (PDBS), poly(di-n-hexylsilane) (PDHS), poly(methylphenylsilane) (PMPS), and poly[bis(p-butylphenyl)silane] (PBPS), which have been reported as active materials in light emitting diodes, have been investigated theoretically through semiempirical (AM1) and ab initio (HF/6-31g) methods and density functional theory using B3LYP parametrization. The AM1 level of calculation predicts the absorption maxima reasonably, but it fails to explain the relative stabilities of the four polysilanes in the excited state. However, calculations based on configuration interaction with single excitation and time-dependent density functional theory suggest additional stabilization in the excited states through intersystem crossing to triplets for PMPS and PBPS, consistent with the experimental observation. In contrast, no such stabilization is predicted for PDBS and PDHS. Furthermore, the existence of a stable triplet state in PMPS may also explain the visible emission observed experimentally in PMPS.

Gauging the significance of atomic oxygen [O(3P)] in sulfoxide photochemistry. A method for hydrocarbon oxidation

A liquid-phase photolysis of 1,2-benzodiphenylene sulfoxide, 1, and dibenzothiophene sulfoxide, 2, was used to generate atomic oxygen [O(3P)] or an equivalent active oxygen species. The reaction for sulfoxide photodeoxygenation was similar to a microwave discharge method for generating O(3P) atoms in the condensed phase (Zadok, E.; Rubinraut, S.; Mazur, Y. J. Org. Chem. 1987, 52, 385-90). Sulfoxide photodeoxygenation is a potentially clean method for O(3P) production compared to the microwave discharge method. With Argon purging of the sulfoxide sample before photolysis, the method can preclude a secondary oxidation process involving molecular oxygen. Our study focused on the results of oxidation products in the reaction of styrene, 3, and on the dependence of substrates that provided an opportunity to vary the electronic and steric effects. The sulfoxide photochemistry is rationalized with the primary formation of O(3P) in which a charge-transfer interaction between O(3P) and substrate precedes oxidation. Functionalization of hydrocarbons takes place under mild photolysis conditions of 1 and 2, which leads to an interesting possibility for the synthetic use of atomic oxygen, O(3P). Alkanes give principally alcohols. Alkenes give principally epoxides and ketones. For comparison, hydroxyl radicals are more reactive and less selective toward hydrocarbons compared to O(3P) atoms. On the other hand, O(3P) atoms balance reactivity and selectivity and involve the oxidation of inert alkanes typically inaccessible to peracid, dioxirane, ozone, and singlet molecular oxygen chemistry. The findings from this study may be useful to those interested in generating high-value oxygenated compounds from readily available petroleum components.