Fluorescence solvatochromic shifts of 4,4′-diaminobiphenyl (DABP) were found to be less than those of 4-aminobiphenyl and the difference mainly occured in hydrogen bonding solvents. This shows that the net effect of hydrogen bonding interactions of two amino groups is less than that of one amino group. The unusual fluorescence red-shift observed for the monocation of DABP relative to the neutral form is not because of the amino group becoming more basic, but because of a large solvent relaxation in aqueous media. As the entire molecule becomes planar upon excitation, its behavior is found to be similar to that of 2,7-diaminofluorene in the S1 state. pKa values for various prototropic reactions in the S0 and S1 states were determined and are discussed.

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Analysis of the absorption and fluorescence characteristics of 4,4'-diaminodiphenylsulfone (4DADPS) in aqueous b-cyclodextrin (b-CDx) solution under different acidic conditions reveals that: (i) the twisted intramolecular charge transfer state (TICT) is more populated than the locally excited (LE) state of 4DADPS in b-CDx; and (ii) the protonation of the monocation of 4DADPS in the S 0 and S 1 states in b-CDx requires more acidic conditions than in the absence of b-CDx. The higher stabilisation of the TICT state compared to the LE state of 4DADPS in b-CDx inclusion complex is contrary to normal observation. This anomalous behaviour is explained by the geometry of the 1: 1 inclusion complex.

A study on the effect of solvents on absorption and fluorescence spectra has indicated that 9-phenanthrol acts as a hydrogen donor in both So and S, states. Fluorimetric titration gives stretched sigmoid curves, giving pK, 9.2 and pK.* 1.8.The effect of solvents and pH on the absorption and fluorescence spectra of naphthylamines 1-4 and naphthyl alcohols 5-8 has been studied extensively. These molecules have certain characteristic features. The fluorimetric titration curves of the former have indicated that there is a lack of correspondence between the removal of naphthylamines and the formation of naphthylammonium ions when the pH is This phenomenon has been attributed to the proton-induced quenching of the amino-compounds' at moderate pH and the formation of naphthylammonium ions take place at lower pH (or in the Hammett acidity scale Ho). In the latter cases, one gets stretched sigmoid curves, giving two inflection points, one corresponding to the ground-state equilibrium and the second to the excited-state equilibrium. Recently it has been observed that the fluorescence of neutral naphthols is quenched diabatically by H+ at a pH approximately between 0 and 1.5 Depending upon the lifetimes of the acid-base species as well as the other rate constants, the intersection of the two curves corresponds to the excited-state equilibrium constant (pK,,*) for 1 -naphthol and ground-state equilibrium constant (PKa) for 2-naphth01.~ Recently, similar behaviour, as observed for naphthylamines, has been noted for phenanthrylamine~.~*~~ The present investigation was carried out t o study the effect of pH on the fluorescence intensity of acid-base species of 9-phenanthrol (POH) and to see whether its behaviour is similar to those of naphthols. The effect of solvents on the absorption and fluorescence spectra has also been studied.

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Development of bimetallic semiconductor oxides with synergistic functions makes a significant advancement in catalytic technologies. This study addresses the preparation of a codoped bimetallic Cd-Ag-ZnO photocatalyst by solvothermal process and its characterization by x-ray diffraction (XRD), high-resolution scanning electron microscopy (HR-SEM), UV-Vis diffuse reflectance spectroscopy (DRS), energy dispersive spectroscopy (EDS), and photoluminescence spectroscopy (PL). XRD and EDS reveal the presence of Cd and Ag in the catalyst. HR-SEM images show plate-like structure of ZnO and the clusters of Cd and Ag on the surface ZnO. Cd-Ag-ZnO has increased absorption in the UV region. This bimetalic photocatalyst shows higher photocatalytic activity for the degradation of Acid Black 1 (AB 1) and Acid Violet 7 (AV 7) under UV light (365 nm) than pure ZnO and commercial TiO2-P25. Cd-Ag-ZnO was found to be stable and reusable without appreciable loss of catalytic activity up to three runs.

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