Irradiation of nitro-PAHs in solution at ambient conditions leads to formation of its lowest excited triplet, dissociation intermediates nitrogen oxide (NO^•) and aryloxy radical (Ar–O^•). Experimental and theoretical studies demonstrated that Franck–Condon excited singlet state S_FC(ππ*) to a receiver, higher-energy triplet state T_n(nπ*) controlled the ultrafast population of the triplet state and, hence, the slight fluorescence yield of nitronaphthalenes. However, the detailed information about the curve-crossings of potential energy surfaces and the major channels for forming T₁ species and Ar–O^• radical were unclear. Here, by using the CASSCF//CASPT2 method, an efficient decay channel is revealed: S_2-FC-1NN → S_2-MIN-1NN or S₂T_3-MIN-1NN → T_3-MIN-1NN or T₃T_2-MIN-1NN→ T_2-MIN-1NN or T₂T_1-MIN-1NN → T_1-MIN-1NN. This explains the high yield of T_1–1NN species and minor yield of Ar–O^• and NO^• radicals. The calculation results suggest the bifurcation processes take place predominantly after the internal conversion to the T_1–1NN state via T₂T_1-MIN-1NN, one leads to T_1-MIN-1NN, while the other to T_1-MIN-ISO to produce Ar–O^• and NO^• radicals.

中文翻译：

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从头算从S发起1-硝基萘的衰减动力学的研究₂（ππ* + N _NO π*）状态

在环境条件下对溶液中的硝基PAHs进行辐照会导致形成最低的三重激发态，离解中间体氮氧化物（NO ^•）和芳氧基（Ar–O ^•）。实验和理论研究表明，Franck–Condon将单线态S _FC（ππ*）激发到接收器，高能三线态T _n（nπ*）控制了三线态的超快填充，因此，荧光体的荧光产量很小。硝基萘。但是，有关势能面的曲线交叉以及形成T ₁物种和Ar–O ^•的主要通道的详细信息激进分子还不清楚。在这里，通过使用CASSCF // CASPT2方法，揭示了一个有效的衰减通道：S _2-FC-1NN →S _2-MIN-1NN或S ₂ T _3-MIN-1NN →T _3-MIN-1NN或T ₃ T _2-MIN-1NN →T _2-MIN-1NN或T ₂ T _1-MIN-1NN →T _1-MIN-1NN。这解释了T _1–1NN物种的高产率和Ar–O ^•和NO ^•自由基的次要产率。计算结果表明，分叉过程主要发生在内部通过T ₂转换为T _1–1NN状态之后。Ť _1-MIN-1NN，一个导致T _1-MIN-1NN，而其他与T _1-MIN-ISO产生的Ar-O ^•和NO ^•自由基。