Used primarily as an intermediate in the synthesis of pharmaceuticals, especially antipsychotic and antidepressant drugs within the phenothiazine class. It serves as a key building block for modifying the phenothiazine core structure to develop active compounds that interact with dopamine and serotonin receptors in the central nervous system. Its chloro group is highly reactive, enabling further substitution with various side chains to produce agents with tailored neurological effects. Also utilized in research for developing novel bioactive molecules and in the preparation of dyes and photoactive materials due to the stability and electronic properties of the phenothiazine ring system.