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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Quantum-Chemical Investigation of the Conformational Dynamics of Mono-meso-phenyl-Substituted Octaalkylporphyrins in the Triplet Excited State
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Quantum-Chemical Investigation of the Conformational Dynamics of Mono-meso-phenyl-Substituted Octaalkylporphyrins in the Triplet Excited State

机译：三重态激发态中单-间-苯基取代的八烷基卟啉构象动力学的量子化学研究

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摘要

The detailed theoretical analysis (semiempirical PM3, DFT, and TD-DFT calculations) of the nature of nonplanar conformations of sterically encumbered mono-meso-phenyl-substituted octaalkylporphyrins in the excited triplet state has been carried out. It was found that the OEP-mesoPh molecule in the triplet excited state may occur in the highly nonplanar conformation characterized by the out-of-plane displacement of the single Cm1-C1 bond and the increased overlap of the porphyrin and the meso-phenyl ring. For the sterically strained porphyrins, the transition into this nonplanar conformation is accompanied by the essential decrease of the vertical triplet-singlet energy gap ΔE_V(T_1-S_0) down to 0.45 eV, in contrast to ΔE_V(T_1-S_0) ～ 1.33 eV for the planar conformation. This leads to the experimentally detected drastic reduction of the triplet state decays for the sterically strained OEP-mesoPh type molecules. The calculated T_1 → T_n transient absorption spectra for planar and nonplanar conformations have been compared with the corresponding experimental data obtained for the investigated compounds. A remarkable accord between experimental results and theoretical calculations on T_1 → T_n absorption spectra in the red and near-IR region provides additional support for the conformational reorganization leading to the formation of the highly nonplanar distortion of OEP-mesoPh molecule in the triplet excited state.
机译：进行了详细的理论分析（半经验的PM3，DFT和TD-DFT计算），对处于激发三重态的位阻单-间-苯基取代的八烷基卟啉的非平面构象的性质进行了分析。发现三重激发态的OEP-mesoPh分子可能以高度非平面构象的形式出现，其特征是单个Cm1-C1键的面外位移以及卟啉和内消旋苯环的重叠增加。对于空间应变的卟啉，向该非平面构象的转变伴随着垂直三重态-单重态能隙ΔE_V（T_1-S_0）的减小，降至0.45 eV，而ΔE_V（T_1-S_0）〜1.33 eV平面构象。这导致实验检测到空间应变的OEP-mesoPh型分子的三重态衰减急剧减少。计算出的平面和非平面构型的T_1→T_n瞬态吸收光谱已与所研究化合物获得的相应实验数据进行了比较。在红色和近红外区域的T_1→T_n吸收光谱的实验结果与理论计算之间的显着一致性为构象重组提供了额外的支持，从而导致三重激发态的OEP-mesoPh分子高度非平面变形的形成。

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