A new series of neutral radicals (DP1-DP6) based on diazaphenalenyl were designed via heteroatomic modifications. As spin sources, the designed radicals were implemented in four different diradical model systems (models I, II, III, and IV) by changing the reference radical and the linkage, and their magnetic interactions between the designed radicals and the reference radical were investigated by using density functional theory calculations. The trend in strength of magnetic interactions of radicals was found to be identical in different model systems. The strength of magnetic interactions could be understood by spin density distributions and NICS values. Our results will be helpful in designing and controlling the organic magnetic materials incorporated with diazaphenalenyl derivatives. In particular, as a new family of spin source radical, DP3 could be a potential candidate in designing new organic magnetic materials due to its strong magnetic coupling and high stability in diradical systems.