The endoperoxide of mesodiphenylhelianthrene MDHPO has been studied in detail with respect to fluorescence and photo-induced rearrangement. MDHPO proved to be non-fluorescent, although its absorption spectrum is dominated at the low energy side by a strong ππ* band with a maximum at 429.5 nm. Irradiation of that band effects rearrangement to the corresponding diepoxide MDHDO, a reaction typical for S1(π*σ*) excited endoperoxides (EPOs). The absorption spectrum of the product MDHDO is blue shifted by only 3.5 nm. MDHDO has the same extended planar aromatic system like its precursor MDHPO, but MDHDO fluoresces strongly. These results set the excitation energy of the S1(π*σ*) state of MDHPO to ≤23 000 cm−1, which is considered to be a generally realistic value of the S1(π*σ*) state energy of aromatic EPOs. The main reaction of S1(π*σ*) excited MDHPO is, however, chemical deactivation to ground state MDHPO via an oxygen biradical. The sequence of O-O bond opening and closing is the general way of repopulation of the S0 state of aromatic EPOs from S1(π*σ*) excited states.
对中二苯基
噻吩 M
DHPO 的内过氧化物进行了详细的荧光和光诱导重排研究。尽管 M
DHPO 的吸收光谱在低能侧主要由一个在 429.5 纳米波长处具有最大值的强ππ* 带所支配,但它被证明是无荧光的。辐照该波段会影响重排生成相应的二
环氧化物 MDHDO,这是 S1(π*σ*)激发的内过氧化物(EPO)的典型反应。产物 MDHDO 的吸收光谱仅蓝移了 3.5 纳米。MDHDO 与其前体 M
DHPO 具有相同的扩展平面芳香系统,但 MDHDO 发出强烈的荧光。这些结果将 M
DHPO 的 S1(π*σ*)态激发能量设定为 ≤23 000 cm-1,这被认为是芳香族 EPO 的 S1(π*σ*)态能量的一般实际值。然而,S1(π*σ*) 激发 M
DHPO 的主要反应是通过氧双自由基
化学失活为基态 M
DHPO。O-O 键打开和关闭的顺序是从 S1(π*σ*) 激发态重新填充芳香族 EPO 的 S0 态的一般方法。