Controlling properties of metal complexes are essential for adopting complexes as photocatalysts. For example, use of solar energy inevitably requires metal complexes absorbing longer wavelength light. Previously, the properties were modulated by changing electronic properties (introduction of electron-donating and electron-withdrawing groups), which resulted in the significant affect on the other properties accompanying decline of photocatalytic activity. In exploring new ways to tune properties, weak interaction between ligands was found to manipulate the ground and excited states of metal complexes. By the weak interaction, photocatalytic ability was increased to a large extent.