光敏化氧化还原反应——Ⅳ.卟啉光敏还原甲基紫精量子产率的测定

光敏还原甲基紫精的产物,正离子自由基(MV⁺)的吸收光谱(ε₆₀₅=1.1×10⁴,ε₃₉₅=3.3×10⁴)和敏化剂的吸收光谱重叠。光照过程中产生的MV⁺,与敏化剂竞争光子,产生屏蔽作用。随着MV⁺浓度的增大,敏化剂在单位时间内所吸收光子数逐渐下降,进而影响这反应量子产率的测定。应用Rougee等人报道的关系式, 对敏化剂所吸收光子分数进行校正,得到一较准确的测定量子产率的方法。全部数据处理在APPLE Ⅱ微机上进行,操作简单,计算快捷。这方法可推广应用到其他产物和吸光分子有重叠吸收光谱的光反应中。

SENSITIZED PHOTO-REDOX REACTION IV. DETERMINATION OF THE QUANTUM YIELD OF THE PORPHYRIN SENSITIZED PHOTOREDUCTION OF METHYL VIOLOGEN

Sensitized photoreduction of methyl viologen produces a cation radical, MV⁺, the absorption spectrum (λ_max 605, ε/ =1.1×10⁴, λ_max395, s=3.3×10⁴) of which overlaps with that of the porphyrin sensitizer. As the MVt starts building up upon irradiation, it competes with the sensitizer for the incoming photons. Therefore, the quantum yield φ, determined experimentally decreases with irradiation time, and deviates considerably from the "real" value. Employing an expression developed by Rougee and coworkers: where f(P, MV⁺) =factor of light absorbed by P where MV⁺ is the only other species absorbing at the region.We developed a way of estimating the fraction of light absorbed by the sensitizer. All the data can be processed in an APPLE Ⅱ microprocessor. This method promised to be generally applicable to other photoreactions with the product having an absorption spectrum overlapping with the light absorbing species.