Here we used the master stability function (MSF) framework to develop a two-dimensional MSF representation that incorporates both real and complex eigenvalues, thereby capturing the dynamics of diagonalizable directed networks. Our analysis shows how synchronization stability depends on complex coupling strengths and reveals conditions under which bounded or unbounded regions of negative MSF arise, corresponding to stable synchronization. This two-dimensional approach unifies periodic and chaotic dynamics within a common framework, offering sharper insights into when and how diagonalizable directed networks can sustain coherent collective behavior.