DFT/TDDFT Study on the Structure and Absorption Spectra of Free Base, N-/Neo-Confused Porphyrin
LIU Guo-kui1, CAO Hong-yu1, 2, LI Shen-min2, TANG Qian1, 2, YANG Yan-jie1, ZHENG Xue-fang1, 2*
1. School of Life Science and Biotechnology, Dalian University, Dalian 116622, China 2. Liaoning Key Laboratory of Bio-organic Chemistry, Dalian University, Dalian 116622, China
摘要： 卟啉类化合物是一类重要的光化学材料，其衍生物特殊的光电特性在各个领域中得到了广泛的应用。利用密度泛函理论(DFT)研究了(free base porphyrin, FBP)及其异构体(neo-confused porphyrin, NECP)和(n-confused porphyrin, NCP)三种卟啉环的几何结构和分子轨道能级。采用TDDFT方法计算真空和溶剂场极化连续模型下三者的吸收光谱。计算表明由于N原子位置变化，FBP，NECP和NCP在Soret带和Q带两个特征吸收峰也有不同。按FBP，NECP和NCP顺序，分子轨道能级LUMO依次降低，HOMO轨道依次升高，从而造成吸收光谱红移。HOMO和HOMO-1轨道能级的分裂造成了FBP和NECP的Soret带的多个吸收峰，而NCP的LUMO和LUMO+1 的能级差与其HOMO和HOMO-1能级差几乎相等造成Soret带只有一个最高吸收峰。计算结果表明不同溶剂(苯、氯仿、乙腈和水)条件下三者的Soret带和Q带特征吸收峰均有显著变化。为此重点讨论了N原子位置的变化及在不同性质溶剂下FBP，NCP和NECP三类化合物Soret带/Q带吸收光谱性质的变化规律和机理。
关键词：氢卟啉;N-混杂卟啉;Neo-混杂卟啉;含时密度泛函;吸收光谱
Abstract：Porphyrin is an important class of photochemical materials, which has been widely used in various fields. Computational investigations into the ground state structures and orbital energy levels of free base porphyrin (FBP), neo-confused porphyrin (NECP) and N-confused porphyrin (NCP) were performed with density functional theory(DFT). Absorption spectra were calculated at TD-B3LYP/6-31+G(d). Degeneracy of HOMO and HOMO-1 is lost, which would account for the shoulder peaks about the most intense transitions of FBP and NECP. Following FBP, NECP and NCP order, the orbital energy level (OEL) of LUMO decreases while the OEL of HOMO increases, which lead to the red shift of adsorption spectra. The energy difference between LUMO and LUMO+1 is almost the same as the difference between HOMO and HOMO-1, which would account for the only most intense transition of NCP. Solvent effect on ground state structures and absorption spectra was also investigated. The data shows that the character peak of Soret band and Q band changes in different solvent (benzene, chloroform, acetonitrile and water). So we further focus on discussing the N atom position and solvent effects on the energy level and Soret/Q bands of FBP, NCP and NECP, as well as clarifying its variation regularity and mechanism.
Key words：Free base porphyrin;N-confused porphyrin;Neo-confused porphyrin;TDDFT;Absorption spectra
刘国魁1，曹洪玉1, 2，李慎敏2，唐 乾1, 2，杨彦杰1，郑学仿1, 2* . 氢卟啉, N-/Neo-混杂卟啉结构和吸收光谱性质的密度泛函理论研究 [J]. 光谱学与光谱分析, 2014, 34(01): 128-132.
LIU Guo-kui1, CAO Hong-yu1, 2, LI Shen-min2, TANG Qian1, 2, YANG Yan-jie1, ZHENG Xue-fang1, 2* . DFT/TDDFT Study on the Structure and Absorption Spectra of Free Base, N-/Neo-Confused Porphyrin . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2014, 34(01): 128-132.
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