Scaling approach for intramolecular magnetic coupling constants of organic diradicals

The intramolecular magnetic coupling constants (J) of 9 diradicals (i-ix) coupled with an aromatic ring were investigated by means of unrestricted density functional theory (DFT) calculations [UB3LYP/6-311++G(d,p)]. For these diradicals, a remarkable linear relationship between the calculated and experimental J values was found. In this study, we suggest that the slope (0.380) of the linear relationship can be utilized as a scaling factor for estimating J values. By applying this scaling factor and calculating J values, we could predict the reliable J values of four dithiadiazolyl (DTDA) diradicals coupled with an aromatic ring. It was also found that this scaling scheme shows a dependence on the length of a coupler. Nevertheless, this scaling approach could be used to estimate J values for diverse diradical systems coupled with a particular coupler by DFT calculations.