Collect. Czech. Chem. Commun. 1994, 59, 1115-1125

Photocolouration of 2,4,4,6-Tetraaryl-4H-thiopyrans: A Semiempirical Quantum Chemical Study

Stanislav Böhma, Pavel Šebekb, Stanislav Nešpůrekc and Josef Kuthana

a Department of Organic Chemistry, Prague Institute of Chemical Technology, 166 28 Prague 6, Czech Republic
b Institute of Organic Chemistry and Biochemistry,Academy of Sciences of the Czech Republic, 166 10 Prague 6, Czech Republic
c Institute of Macromolecular Chemistry,Academy of Sciences of the Czech Republic, 162 06 Prague 6, Czech Republic


Molecular geometries of 4H-thiopyrans Ia, Ib and their possible photoisomers IVa - VIIa and IVb - VIIb were optimized by the AM1 and PM3 method and used for the calculation of electronic absorption spectra by the CNDO/S-CI procedure. Comparison of the theoretical data with experimental UV-VIS absorption spectra made it possible to postulate two probable mechanisms of the photocolouration of Ia, Ib caused by sunlight or UV-illumination.