A Novel 'On-Off' Rhodamine Based Sensor for Colorimetric Detection of CN-and Its Application as Encoder-Decoder and Molecular Keypad Lock

A novel rhodamine-phenalenedicarbonitrile based on-off sensor (Rho-Pdc) has been synthesized which is characterized by H-1 NMR, C-13 NMR and mass spectrometry. The photophysical studies of the dyad suggest its existence in spirolactam ring open form of rhodamine. ICT (Intramolecular Charge Transfer) active sensor displays an absorption band at 577 nm with a shoulder at 520 nm and fluorescence band at 593 nm. The treatment of dyad Rho-Pdc with different anions shows its sensitivity and selectivity towards CN- ions in aqueous methanolic solution with lowest detection limit of 0.13 mu M and the binding constant was determined to be 1.17 x 10(4) M-1 by applying Benesi-Hildebrand equation. The presence of CN- ions hinder the ICT process of dyad Rho-Pdc and shows a blue shift in absorption band of dyad Rho-Pdc with formation of new band at 488 nm as well as decrease in the intensity of emission band. Rho-Pdc has also been used for the colorimetric detection of CN- ions among different anions and concentrations. The reversibility of Rho-Pdc.CN(-)complex has been achieved with Fe3+ ions which formed the basis for the construction of multiple molecular logic circuits.