Neeraj Kumar Joshi

Fluorescence characteristics of 5-amino salicylic acid: An iodide recognition study

In this paper we report the effect of iodide on the fluorescence of 5-amino salicylic acid (5-ASA). In the absence of iodide, prominent blue green (BG) emission band at ∼465nm (broad) is observed in aprotic solvents whereas violet (V) emission at ∼408nm, blue green (BG) at ∼480nm and green (G) at ∼500nm are observed in case of protic solvents. On the addition of iodide ion (I(-)), the intensity of BG fluorescence is enhanced in case of aprotic solvents. On the other hand the G band is enhanced in protic solvents and decrease in the intensity of the V band is observed. The effect of hydrogen bonding as well as the interplay of neutral and ionic species is invoked to explain the observed results. The study projects the application of this system in iodide recognition in protic/aprotic environments.

Steady state and time-resolved fluorescence study of isoquinoline: reinvestigation of excited state proton transfer.

In the present work we report some hitherto unnoticed features in the steady state and time-resolved measurements of isoquinoline in water and trifluoroethanol (TFE). Absorption spectra reveal that in water, neutrals as well cationic species are present. Emission spectrum shows structured features at shorter wavelengths accompanied with a broad band around 375 nm, which correspond to neutrals and cations respectively. However, time-resolved data indicate that protonation does not take place in the excited state in water. On the contrary, in stronger hydrogen bonding solvent TFE, distribution of decay components is observed and at longer wavelengths a small rise time is present. This is ascribed to neutral and cation-like species present in the ground as well as in the excited state. The difference in the results is explained in terms of different excited state potential energy surfaces for water and TFE; particularly, the presence of a rather small barrier for protonation in case of TFE.

Photochemistry and excited state prototropic behaviour of 8-amino 2-naphthol

In the present work, photophysical behaviour of 8-amino 2-naphthol in various solvents as well as at various pH values has been investigated. Various ground and excited state species are noticed. It exhibits a completely different photo prototropic behaviour as compared to its parent molecule 2-naphthol. The spectral and transient studies indicate that at lower pH values, equilibrium between cation and neutral exists in the excited state. At neutral pH some peculiar behaviour in its spectral properties is noticed.