The intramolecular magnetic coupling constant (J) of 9 diradicals (i-ix) coupled with an aromatic ring were investigated by means of unrestricted density functional theory (DFT) calculations [B3LYP/6-311++G(d,p)]. For those diradicals, the linear correlation was found between the calculated and experimental J values on the basis of results of the linear regression analysis. In this study, we suggest that the value of slope (0.380) of linear regression can be used as scaling factor for estimating the accurate J values. In fact, DFT calculations overestimate the J values significantly. By applying this scaling factor to the calculated J values, we can predict the reliable J values of four DTDA diradicals (x-xiii) coupled with an aromatic ring. It also found that certain scaling factors have a restricted application depending on the length of a coupler unit. In conclusion, this approach, which uses a scaling factor, can be used to estimate the accurate J values for diverse diradical systems coupled with a particular coupler using DFT calculations.
Figure 1. Correlation between calculated and experimental J values (cm-1) for 9 diradicals (i-ix) coupled with an aromatic ring.