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Two pyran based bipodal D–π–A systems, CAPBA and CAPTBA, have been developed as Hg2+ ion selective colorimetric and fluorescent ratiometric probes. Both probes formed a 1 : 2 complex, with two mercury ions per probe. The stoichiometry of binding, limit of detection and binding constants were determined using absorption and fluorescence spectroscopy. The metal ion complexation proceeds with deprotonation of the NH protons of the barbituric acid or thiobarbituric acid moiety which was characterized using 1H NMR spectroscopy and MALDI-TOF mass spectrometry. Fluorescence lifetime studies ascertained the formation of a static complex. DFT computations at the B3LYP and CAM-B3LYP levels of theory corroborated the experimental findings and further supported the deprotonation process during complex formation. The complexation is found to be reversible on treatment with cysteamine hydrochloride.

A series of pyran based Donor-π-Acceptor (D-π-A) systems have been synthesized and used as sensitizer in Dye-Sensitized Solar Cell (DSSC), in which phenothiazine (PH), triphenylamine (TPA), methoxy phenyl amino styryl (ATPA), diethyl aniline (EA) and carbazole (CA) were used as electron donors and barbituric acid as electron acceptor. The optical, electrochemical, theoretical and photovoltaic studies are carried out. The devise with PHPBA as sensitizer achieved the highest solar energy-to-electricity conversion efficiency (η) of 1.16%.

The nonlinear optical (NLO) properties of a series of pyran based bipodal D–π–A molecules have been studied experimentally and theoretically. The bipodal D–π–A molecules prepared exhibited a very high NLO response depending on the electron donating ability of the donor moiety. In the prepared series, the molecule with dianisylphenylamine (DAPA) as the donor showed the maximum value for the TPA coefficient (β) for a given acceptor unit. The static dipole moment (μtot), mean polarizability (αtot), polarizability anisotropy (Δα), static first order hyperpolarizability (βtot) and second order hyperpolarizability (γtot) were calculated by using DFT at the B3LYP/6-311++G(d,p) level of theory. The trend obtained for the computed hyperpolarizability (βtot) values is in line with the trend in the experimentally obtained values of the TPA coefficient (β) with the variation in the donor capacity.

A multimode ratiometric Hg2+ selective chemosensor system based on a carbazole–thiobarbituric acid conjugate (CTBA) was developed. Its colorimetric and fluorescence behavior towards Hg2+ ions in both homogeneous and microheterogeneous media were investigated. A ratiometric mode of response of absorption as well as fluorescence in acetonitrile and 9 : 1 THF/H2O medium was observed in the presence of Hg2+ ions. The sensing mechanism involves formation of a 1 : 2 CTBA : Hg2+ complex by deprotonation of imide protons of the thiobarbituric acid unit. The complex formation can be reversed by using competing ligands such as cysteamine hydrochloride.