ABSTRACT
A phenolphthalein-based Schiff base, 3,3-bis-{4-hydroxy-3-[(pyridine-2-ylmethylimino)-methyl]-phenyl}-3H-isobenzofuran-1-one (PAP), has been synthesized and used for selective fluorescence 'turn on' and 'turn off' sensing of Zn2+ and PO43- respectively. The limit of detection using the 3σ method for Zn2+ is found to be 19.3 nM and that for PO43- is 8.3 µM. The sensing mechanism of PAP for Zn2+ ions has been explained by 1H NMR, 13C NMR, TRPL, ESI-MS, FT-IR, and DFT based calculations. Taking advantage of this fluorescence 'on-off' behavior of PAP in the sequential presence of Zn2+ and PO43- a two input fuzzy logic (FL) operation has been constructed. The chemosensor PAP can thus act as a metal ion and anion responsive molecular switch, and its corresponding emission intensity is used to mimic numerous FL functions. To replace various expensive, time-consuming experimental procedures, we implemented machine learning soft computing tools, such as fuzzy-logic, artificial neural networks (ANNs), and adaptive neuro-fuzzy inference systems (ANFIS), to correlate as well as predict the fluorescence intensity in the presence of any equivalent ratio of Zn2+ and PO43-. The statistical performance measures (MSE and RMSE, for example) show that the projected values of the cation and anion sensing data by the ANFIS network are the best and closer to the experimental values.
ABSTRACT
CONTEXT: Quantum mechanical calculations involving electron correlation, frequency dispersion, and solvent effects were carried out to examine the second-order nonlinear optical response of various acceptor, X (-CF3, -CN, -NO2) substituted in N,N-dimethylaniline (DMA) and julolidine(JLD). Here, both DMA and JLD acts as donor and the three substituted groups, X (-CF3, -CN and -NO2) at the para position of both the ring systems as acceptor. The NLO response (ßHRS) of -CF3 and -CN substituted DMA and JLD is relatively lower compared to DMA-NO2 and JLD-NO2. The charge distribution is found higher in case of -NO2 substituted DMA and JLD (±443 and ±449) compared to their -CF3 or -CN substitution. Electronic characteristics such as UV-Vis absorption spectra, crucial excited state parameters and charge transfer contribution to ßHRS have been used to explain the NLO parameter of DMA-X and JLD-X. Variation of the incident optical frequency of light shows fluctuation of ßHRS value and highest values of ßHRS are obtain at the λmax frequency of each compound. Solvent polarity variation study on ßHRS shows that ßHRS varies linearly with the Kirkwood-Onsagar dielectric factor (D). METHODS: All computational studies have been carried out using density functional theory (DFT) based method. Since CAM-B3LYP based hybrid functional improves the asymptotic behavior of the exchange interaction by dividing into short-range and long-range components, first hyperpolarizability values in the present study were computed using DFT/ CAM-B3LYP/ 6-31G+(d,p) level of theory.
