Spiropyrans and spirooxazines (SP) are known to undergo photochromism to form merocyanines (MC). In this study, upon pulsed electron radiolysis of SP in organic solvents, we observed the transient absorption spectra of SP radical ions in the visible wavelength region. Based on first-order kinetics in the microsecond time domain, the absorption spectra changed to different ones, which were plausibly due to the radical ions of the corresponding MC. The reaction rates from SP radical ions to MC ones were determined. Using heats of formation for the radical ions of SP and MC evaluated with DFT calculations, the differences in heats of formation between the radical ions of SP and MC were determined to be exothermic. The reaction rate correlated with the difference in heat of formation, which depended on the parity of the radical ions. Time-dependent DFT calculations provided the SOMO surfaces of the radical ions of SP and MC. Comparing the SOMO with the LUMO, HOMO, and HOMO-1 surfaces of the neutral SP, we found that the attached electron locates on the LUMO upon one-electron reduction in SP, whereas the HOMO-1 of SP is involved in one-electron oxidation of SP rather than the HOMO.

中文翻译：

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通过脉冲电子辐射分解和 DFT 计算研究的自由基离子对螺吡喃的放射变色作用


已知螺吡嗪和螺噁嗪 （SP） 会发生光致变色形成美菁 （MC）。在这项研究中，在有机溶剂中对 SP 进行脉冲电子辐射分解后，我们观察到了 SP 自由基离子在可见光波长区的瞬态吸收光谱。基于微秒时域中的一阶动力学，吸收光谱变为不同的光谱，这很可能是由于相应 MC 的自由基离子造成的。测定 SP 自由基离子与 MC 自由基离子的反应速率。使用通过 DFT 计算评估的 SP 和 MC 自由基离子的形成热，确定 SP 和 MC 自由基离子之间的形成热差异是放热的。反应速率与形成热的差异相关，这取决于自由基离子的奇偶性。将 SOMO 与中性 SP 的 LUMO、HOMO 和 HOMO-1 表面进行比较，我们发现 SP 中的单电子还原后，附着的电子位于 LUMO 上，而 SP 的 HOMO-1 参与 SP 的单电子氧化而不是 HOMO。