Diradical Characters of s-Indaceno[1,2,3-cd;5,6,7-c’d’]Diphenalene with and without Interaction with MgO(001)

Abstract

Diradical character is important for investigating and predicting the functions of singlet biradical molecules. Singlet biradical molecules possess many unique properties, and their immobilisation by surfaces has been extensively studied for applications in devices, such as quantum computers, single-molecule magnets, single-atom catalysts, organic batteries, and organic superconductivity devices. Recently, an estimation scheme of diradical character from the calculated results of density functional theory with plane-wave basis (DFT/plane-wave), which is a general method for calculating the electronic structures of surfaces, was developed by our research group. This scheme enables us to investigate the diradical character of the open-shell structure stabilised by the surfaces. In this study, DFT/plane-wave calculations for s-indaceno [1,2,3-cd;5,6,7-c'd']diphenalene molecules, whose diradical character was experimentally observed, were performed. Using the developed scheme, it was verified whether the diradical character was modulated by the interaction with the MgO(001) surface. The calculated results showed that the diradical character increased as the distance from the surface decreased, although the enhancement effect of the surface was inhibited by the steric hindrance of the substituents.

Model calculations for the prediction of the diradical character of physisorbed molecules: p-benzyne/MgO and p-benzyne/SrO

“…Eqn ( 4) can be applied easily to the results of DFT/plane-wave calculations, and the accuracy of this approximation has been well discussed in previous studies. 20,[29][30][31] The equation is a good approximation for analysing the diradical character of singlet biradicals, such as p-benzyne. In this study, the y values were expressed as percentages and, therefore, were multiplied by 100.…”

“…m-benzyne), and hybrid-DFT or DFT+U methods should be used when calculating such molecules. 29,31 The hybrid-DFT method, which has a smaller self-interaction error than the pure-DFT method, provides more accurate results. 1,29 However, the computational cost of the hybrid-DFT method is high, and the U dependency of the calculated y values by the DFT+U method has not been discussed in detail for organic biradicals.…”

“…Furthermore, the diradical characters of stable organic radicals, such as diphenalenes, with and without surface adsorption, were estimated. 29,31 The previous study showed that the diradical character of an organic molecule can be varied by its interaction with surfaces, even when the surface-molecule distance is in the physisorption region. 31 However, in that study, the geometries of the organic molecules were fixed, and the adsorption site dependence was not discussed because of the computational cost.…”

“…29,31 The previous study showed that the diradical character of an organic molecule can be varied by its interaction with surfaces, even when the surface-molecule distance is in the physisorption region. 31 However, in that study, the geometries of the organic molecules were fixed, and the adsorption site dependence was not discussed because of the computational cost. In addition, the cell length, which corresponds to the intermolecular distance, was fixed.…”

“…[36][37][38] MgO(001) is known as a stable and bulky surface and has been employed both experimentally and theoretically to study surface-adsorbed magnetic elements. 20,26,27,31,[39][40][41][42][43] Geometry optimisation was performed on these models to investigate the structural changes caused by adsorption and the effects of the adsorption sites. In addition, using model calculations with different lattice lengths and cell sizes, we investigated whether the intermolecular distance affected the diradical character.…”