Symmetric and disulfide linked reversible fluorescent organic material: a chemosensor for Pb2+ ion and its applications in real world sample analysis

•Disulfide linked reversible and symmetric fluorescent organic material as a fluorescent chemosensor Cysal for Pb2+ ions.•The mutual PET – ESIPT process is proposed as a “Switch off-on” mechanism for a specific recognition of Pb2+ ions at the physiological pH range.•The binding constant and limit of detection of the probe Cysal for Pb2+ ions were obtained as 3.02×104 M−1 and 2.2×10−2 µM respectively.•Real level samples from water, soil and fairness cream were tested for the detection of Pb2+ ions including the bioimaging studies.