Hypochlorite (ClO^-) has been widely used as the main component of cleaning agents, and is also used in the treatment of disinfect water. The concentration of ClO^- is critical for living organisms and the environment. Hence, it is essential to develop reliable, sensitive and user-friendly molecular sensors to determine ClO^-. In this context, the synthesized probe 2,4-di-tert-butyl-6-((E)-(((E)-(9-pentyl-9H-carbazol-3-yl)methylene) hydrazono) methyl) phenol (TBCP) can detect ClO^- with rapid response (1 min), low detection limit (0.28 μM) and high sensitivity. Also, the sensor is utilized at wide pH range (4–10) for the determination of ClO^-. TBCP showed outstanding selectivity for ClO^- over other competing analytes via a fluorescent response change from colorless to orange, and its response mechanism was based on a deprotonation phenomenon. The ClO^- level was successfully determined by TBCP on test kits, cotton swabs and in real samples. Fluorescent bio-imaging of ClO^- in HEPG2 cells was also carried out in the presence of TBCP. Furthermore, DFT calculations were performed successfully for TBCP and TBCP + ClO^- complex.