= Pradeep K. Sengupta
{c}
\b[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>.<Excited state proton-transfer spectroscopy of 3-hydroxyflavone and quercetin by Pradeep K. Sengupta and Michael Kasha>[Original full byline and Abstract, printed p.382]{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.<Excited state proton-transfer spectroscopy of 3-hydroxyflavone and quercetin by Pradeep K. Sengupta and Michael Kasha>[Printed p.384, excitation spectra for the two luminescence regions]{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 give
$$
I_1(\lambda)=C_1g(\lambda),\qquad I_2(\lambda)=C_2g(\lambda).
$$
Normalizing 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.<Excited state proton-transfer spectroscopy of 3-hydroxyflavone and quercetin by Pradeep K. Sengupta and Michael Kasha>[Printed p.384, Figure4]{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.
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