Theoretical investigation of structure diversity and electronic properties in the series isomeric [26]hexaphyrin (1.1.1.1.1.1) and [28]hexaphyrin (1.1.1.1.1.1)

Abstract In this work, [26]hexaphyrin (1.1.1.1.1.1) and corresponding [28]hexaphyrin (1.1.1.1.1.1) with different structures have been investigated using density functional theory (DFT) and time-dependent DFT. The frontier molecular orbitals (FMOs), aromaticity, electronic spectra and nonlinear optical properties were systematically investigated. Significantly, thienyls groups on the meso -carbon have great influence on the electronic properties. Based on an analysis of orbital composition, contribution of the thienyls to FMOs concentrates primarily on HOMO and third highest occupied molecular orbital (HOMO−2) to aromatic molecules, and focuses on second highest occupied molecular orbital (HOMO−1) to antiaromatic molecules. In addition, the first hyperpolarizability ( β 0 ) values of dumbbell-shape and rectangular-shape molecules are significantly lower than those of the other three molecules. For the other three molecules with both aromatic molecules and antiaromatic molecules, their β 0 values have the same regularities that are in the orders of triangular-shape  β 0 value of antiaromatic molecules is greater than that of aromatic molecules because of their different transition properties. We hope that this work will provide valuable information for adjusting electro-optical properties by changing substituent group on the meso -carbon, aromaticity and configuration.