Wang Qi, Song Meiyu, Song Xinyu, Bu Yuxiang
School of Chemistry and Chemical Engineering, Shandong University, Jinan, 250100, People's Republic of China.
Phys Chem Chem Phys. 2019 Aug 21;21(31):17209-17220. doi: 10.1039/c9cp02691f. Epub 2019 Jul 25.
Porphyrin derivatives with inverted pyrrole rings have been experimentally synthesized, and their relevant electronic and magnetic properties have great application prospects in terms of electronic devices. In this work, we rationally design the structures and computationally investigate the electronic properties of porphine and Mg/Zn-porphyrin derivatives with two inverted pyrrole rings, i.e. the dipyrrole-inverted porphine and Mg/Zn-porphyrin analogues (1NN-2H, 2NN-2H, 1NN-Mg, 2NN-Mg, 1NN-Zn and 2NN-Zn), at the B3LYP/6-311G(d,p) level. The main structural characters of these porphyrin derivatives are that the [double bond splayed left]NH units of two pyrrole rings are inverted outwards and the porphyrin-like macrocycles are distorted from square to diamond shapes. More interestingly, these dipyrrole-inverted porphyrin derivatives present diradical characters with noticeably large antiferromagnetic spin coupling constants, i.e.-982.2/-936.3 cm for 1NN-2H/2NN-2H, -796.3/-764.2 cm for 1NN-Mg/2NN-Mg and -1044.5/-1055.2 cm for 1NN-Zn/2NN-Zn, but their monopyrrole-inverted counterparts do not. Examinations of the orbital properties featuring large occupation numbers of the lowest unoccupied natural orbitals and two singly occupied molecular orbitals that are polarized in opposite directions also confirm these findings. These porphyrin derivatives have small singlet-triplet energy gaps and small energy gaps between the highest occupied molecular orbital and lowest unoccupied molecular orbital of the closed-shell singlet states. These are conducive to the emergence of diradical character and large spin coupling constants. Furthermore, the spin-alternation analyses show that each dipyrrole-inverted porphyrin derivative has two resonant structures featuring two spin-opposite single electrons, in agreement with the observed antiferromagnetic spin couplings. This work provides novel insights into the electronic structures and properties of the porphyrin derivatives with modified structures and also provides helpful information for the rational design, synthesis and characterization of new porphyrin-based magnets.
具有反向吡咯环的卟啉衍生物已通过实验合成，其相关的电子和磁性特性在电子器件方面具有巨大的应用前景。在这项工作中，我们合理设计了具有两个反向吡咯环的卟吩和Mg/Zn-卟啉衍生物（即双吡咯反向卟吩和Mg/Zn-卟啉类似物（1NN-2H、2NN-2H、1NN-Mg、2NN-Mg、1NN-Zn和2NN-Zn））的结构，并在B3LYP/6-311G(d,p)水平上对其电子性质进行了计算研究。这些卟啉衍生物的主要结构特征是两个吡咯环的[双键向左展开]NH单元向外反转，且卟啉样大环从方形扭曲为菱形。更有趣的是，这些双吡咯反向卟啉衍生物呈现双自由基特征，具有明显较大的反铁磁自旋耦合常数，即1NN-2H/2NN-2H为-982.2/-936.3 cm，1NN-Mg/2NN-Mg为-796.3/-764.2 cm，1NN-Zn/2NN-Zn为-1044.5/-1055.2 cm，但它们的单吡咯反向对应物则没有。对具有大量最低未占据自然轨道占据数以及两个方向相反极化的单占据分子轨道的轨道性质进行研究也证实了这些发现。这些卟啉衍生物具有较小的单重态-三重态能隙以及闭壳单重态的最高占据分子轨道和最低未占据分子轨道之间的小能隙。这些有利于双自由基特征和大自旋耦合常数的出现。此外，自旋交替分析表明，每个双吡咯反向卟啉衍生物都有两个具有两个自旋相反单电子的共振结构，这与观察到的反铁磁自旋耦合一致。这项工作为具有修饰结构的卟啉衍生物的电子结构和性质提供了新的见解，也为新型卟啉基磁体的合理设计、合成和表征提供了有用信息。
