Pradeep K. Sengupta

Pradeep K. Sengupta is first author, with Michael Kasha, of the 1979 investigation connecting the unusual fluorescence of 3-Hydroxyflavone and quercetin with excited-state intramolecular proton transfer.^[ref] The study compared optical observations under different environments, rather than assigning a mechanism from a single emission maximum.

One informative comparison concerns excitation spectra: the authors reported that the violet and green emissions could share the same excitation spectrum under their low-temperature conditions.^[ref] That supports a common initially absorbing species, while allowing different processes after excitation. It does not require identical emitting molecular structures.

An original test illustrates the logic. Suppose a corrected excitation profile is $g(\lambda )$ and two emission channels giveNormalizing each channel removes its constant amplitude, revealing matching shapes. At chosen excitation wavelengths where $g$ is $(1,2,1)$, signals $(3,6,3)$ and $(7,14,7)$ differ in brightness but have identical normalized profiles. A contaminant whose absorption happened to have the same profile would not be excluded by this comparison alone.

Complementary temperature and deuteration measurements therefore matter: they change the competition among pathways while testing a common interpretation. The paper discusses deuteration effects on relative emission.^[ref] The numerical profiles above are original examples, not the reported spectra. Together these comparisons show why a mechanism gains support from several different experimental perturbations.