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The Photochemical Behavior of Colchicone and Thiocolchicone
Author(s) -
Bussotti Laura,
D'Auria Maurizio,
Foggi Paolo,
Lesma Giordano,
Righini Roberto,
Silvani Alessandra
Publication year - 2000
Publication title -
photochemistry and photobiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.818
H-Index - 131
eISSN - 1751-1097
pISSN - 0031-8655
DOI - 10.1562/0031-8655(2000)0710029tpboca2.0.co2
Subject(s) - conrotatory and disrotatory , photoisomerization , excited state , photochemistry , singlet state , chemistry , molecular orbital , singlet fission , ring (chemistry) , ground state , spectroscopy , atomic physics , molecule , physics , catalysis , biochemistry , organic chemistry , isomerization , quantum mechanics
ABSTRACT The irradiation of colchicone 5 led to the formation of lumicolchicone 7 . The same reaction cannot be obtained by using thiocolchicone 6 as substrate. Transient absorption spectroscopy of colchicone and β‐lumicolchicone showed that probably the photoisomerization occurred on colchicone in its first excited singlet state. The spectroscopic data are in agreement with the hypothesis that lumicolchicone was generated in the ground state from the S 1 state of colchicone without the presence of any intermediate. Semiempirical calculations on colchicone and thiocolchicone showed that the highest single occuped molecular orbital and the lowest unoccupied molecular orbital of the singlet excited colchicone can give a disrotatory ring closure to 7 , while thiocolchicone cannot give the same type of process.