Charge-transfer states refer to the electronic states in molecular systems where an electron is transferred from one molecular unit to another. These states play a crucial role in various processes such as photoinduced charge transfer, organic photovoltaics, and fluorescence quenching. Understanding and characterizing charge-transfer states is essential for the development of new materials and technologies in fields such as optoelectronics, catalysis, and sensor applications. Researchers study the dynamics, energetics, and properties of charge-transfer states to gain insights into their behavior and potential applications.