Photochemical ionization of the triarylmethane leuconitriles
Photochemical ionization of the triarylmethane leuconitriles
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三芳基甲烷无色腈的光化学电离
DOI：
10.1002/chin.197605097
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发表时间：
1975
期刊：
影响因子：
--
通讯作者：
M. Herz
中科院分区：
文献类型：
--
作者：
M. Herz
在乙醇中照射后，三芳基甲烷无色腈通常会发生异裂，形成染料阳离子和氰化物离子。已经获得了一系列这些无色腈的吸收和发射光谱以及裂解的量子产率。观察到激发能完全转移到具有最低单线态能量的亚甲基绝缘发色团，导致不同程度效率的光电离（裂解）。激发分子是否光电离、发出荧光或衰变至基态取决于特定激发单线态的性质。光电离效率会因竞争性进行系间交叉的发色团（例如卤素、羰基或硝基取代的无色腈）或荧光增强的发色团（例如萘基取代的无色腈）而降低。孔雀石绿无色腈 2a (MGLN) 作为光量计的使用已得到广泛认可。 1· 2 其用于此目的取决于光电离，光电离在极性溶液中以高量子效率发生，形成高度彩色的染料阳离子 (2b)。这种光化学反应发生在化合物的整个光谱吸收范围内，3 与光强度4 和温度无关。 5 由于这些原因，这种无色腈提供了一种敏感的分子系统，很容易适合进行光量测量，特别是在低光强度下。尽管已经报道了许多关于三芳基甲烷白腈的光致变色的研究，但尚未推测光致变色反应的光化学机制。为此，我们测量了一系列取代三芳基甲烷 (1-14) 的光谱和光电离效率。所选化合物具有相同的骨架结构，因此有助于结构-活性关系的研究。人们还预计，相关光化学的阐明可能会导致可用作光谱可见区光量计的化合物。乙醇中光电离 (ipc) 的量子产率
Upon irradiation in ethanol, the triarylmethane leuconitriles generally undergo a heterolytic cleavage to form dye cation and cyanide ion. The absorption and emission spectra have been obtained for a series of these leuconitriles along with the quantum yields of the cleavage. Complete transferof the excitation energy to the methylene-insulated chromophore with the lowest singlet energy leading to the photoionization (cleavage) with varying degrees of efficiency was observed. Whether the excited molecule photoionizes, fluoresces, or decays to itsground state is dependent on the nature of the particular excit-ed singlet state. The efficiencyof the photoionization is reduced eitherwith chromophores which competitively undergo intersystem crossing, such as the halogen-, carbonyl-, or nitro-substituted leuconitriles, or with those which exhibit increased fluorescence, such as the naphthyl-substituted leuconitrile.The use of Malachite Green Leuconitrile 2a (MGLN) as an actinometer is well established. 1· 2 Its use for this purpose depends upon a photoionization, which occurs with high quantum efficiency in polar solution forming a highly col-ored dye cation (2b). This photochemical reaction takes place throughout the entire spectral absorption range of the compound, 3 independent of light intensity4 and tempera-ture. 5 For these reasons, this leuconitrile provides a sensi-tive molecular system easily adapted for making actinome-tric measurements, especially at low light intensities. Al-though numerous studies of the photochromism of the triar-ylmethane leucontriles have been reported, a photochemical mechanism for the photocoloration reaction has yet to be postulated. Toward this end, we have measured the spectra and photoionization efficiencies for a series of substituted triarylmethanes (1-14). The compoundsselected have the same skeletal structure, and thus lend themselves to the study ofstructure-activity relationships. It was also antici-pated that elucidation of the pertinent photochemistry might lead to compounds useful as actinometers into the visible region of the spectrum. The quantum yield of photoionization (ipc) in ethanol for