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首页> 外文期刊>ACS Omega >Substituent Effect in the First Excited Triplet State of Monosubstituted Benzenes
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Substituent Effect in the First Excited Triplet State of Monosubstituted Benzenes

机译：在第一激发三胞胎单位苯并中的取代基效应

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The structure of 30 monosubstituted benzenes in the first excited triplet T_(1) state was optimized with both unrestricted (U) and restricted open shell (RO) approximations combined with the ωB97XD/aug-cc-pVTZ basis method. The substituents exhibited diverse σ- and π-electron-donating and/or -withdrawing groups. Two different positions of the substituents are observed in the studied compounds in the T_(1) state: one distorted from the plane and the other coplanar with a quinoidal ring. The majority of the substituents are π-electron donating in the first group while π-electron withdrawing in the second one. Basically, U- and RO-ωB97XD approximations yield concordant results except for the B-substituents and a few of the planar groups. In the T_(1) state, the studied molecules are not aromatic, yet aromaticity estimated using the HOMA (harmonic oscillator model of aromaticity) index increases from ca. ?0.2 to ca. 0.4 with substituent distortion, while in the S_(1) state, they are only slightly less aromatic than in the ground state (HOMA ≈0.8 vs ≈1.0, respectively). Unexpectedly, the sEDA(T_(1)) and pEDA(T_(1)) substituent effect descriptors do not correlate with analogous parameters for the ground and first excited singlet states. This is because in the T_(1) state, the geometry of the ring changes dramatically and the sEDA(T_(1)) and pEDA(T_(1)) descriptors do not characterize only the functional group but the entire molecule. Thus, they cannot provide useful scales for the substituents in the T_(1) states. We found that the spin density in the T_(1) states is accumulated at the C_(ipso) and C_(p) atoms, and with the substituent deformation angle, it nonlinearly increases at the former while decreases at the latter. It appeared that the gap between singly unoccupied molecular orbital and singly occupied molecular orbital (SUMO-SOMO) is determined by the change of the SOMO energy because the former is essentially constant. For the nonplanar structures, SOMO correlates with the torsion angle of the substituent and the ground-state pEDA(S_(0)) descriptor of the π-electron-donating substituents ranging from 0.02 to 0.2 e . Finally, shapes of the SOMO-1 instead of SOMO frontier orbitals in the T_(1) state somehow resemble the highest occupied molecular orbital ones of the S_(0) and S_(1) states. For several planar systems, the shape of the U- and RO-density functional theory-calculated SOMO-1 orbitals differs substantially.
机译：在第一激发三态T_（1）状态下的30个单溶质苯的结构是用不受限制的（U）和限制的开口壳（RO）近似优化了与ωb97xd/八cc-pvtz基础方法的优化。取代基表现出不同的σ-和π-电子给予和/或 - 绘制组。在T_（1）状态的研究中观察到取代基的两种不同位置：用Quinoidal环从平面和其他共面扭曲的化合物中。大多数取代基是π-电子在第一组中提供，而在第二个中π电子取出。基本上，U-和RO-ωb97xd近似值，除了B-取代基和少数平面组外，还产生一致的结果。在T_（1）状态下，研究的分子不是芳族的，但使用HOMA（芳香性的谐振子模型）指数估计的芳香性从CA增加。 ？0.2到CA. 0.4具有取代基失真，而在S_（1）状态下，它们的芳族略少于地面状态（分别为HOMA≈0.8Vs≈1.0）。出乎意料地，SEDA（T_（1））和PEDA（T_（1））取代基效应描述符与地面的类似参数和第一激发单态的取代基效应描述符不相关。这是因为在T_（1）状态下，环的几何形状急剧地改变，并且SEDA（T_（1））和PEDA（T_（1））描述符不表征功能组而是整个分子。因此，它们不能为T_（1）状态中的取代基提供有用的尺度。我们发现，T_（1）状态中的旋转密度在C_（IPSO）和C_（P）原子中累积，并且具有取代基变形角度，它在前者处非线性地增加，而后者的减少。似乎单独未占用的分子轨道和单独占用的分子轨道（SUMO-SOMO）之间的间隙由SOMO能量的变化决定，因为前者基本恒定。对于非平面结构，SOMO与取代基的扭转角和地态PEDA（S_（0））描述符与0.02-0.2℃的π-电子给予的取代基的描述符相关。最后，SOMO-1的形状而不是SOMO前沿轨道在T_（1）状态以某种方式类似于S_（0）和S_（1）状态的最高占用的分子轨道。对于几个平面系统，U-和RO密度函数理论计算的SOMO-1轨道的形状基本上不同。

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