ISSN:
1434-4475
Keywords:
Bile pigments
;
Photochemistry
;
Photoisomerization
;
Radiationless deexcitation
;
Reaction dichotomy
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Pyrromethenones are isomerized into their diastereomers at the exocyclic double bond by light, whereas dipyrromethenes and methylenepyrrolylmethyllenepyrrolinones as well as integral bile pigments containing these two partial structures (biliviolines, biliverdines) are not. The reason for this dichotomy was shown by investigation of model compounds to be neither the thermodynamically and kinetically instable product nor the availability of low states of lone pair character. Instead the very efficient radiationless decay of the excited singlet proceeds via a desactivation process being a tunneling between excited and ground state potential surfaces. Calculations according to this theory ofFormosinho affords quantitative results which are in excellent agreement with experimental data. Another desactivation mode comes from the crossing of the potential surfaces of the ground state of one tautomeric form with those of the excited state of another, leading to a proton transfer process. The molecular basis of these processes is shown to be inter—as well as intramolecular hydrogen bonding.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00910961
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