Novel preparation and photochromic properties of 2,4,4,6-tetraaryl-4H-thiopyrans

• Published in: J. Chem. Soc., Perkin Trans. 2 no. 8; pp. 1301 - 1308
• Main Authors: Šbebek, Pavel, Nešpůrek, Stanislav, Hrabal, Richard, Adamec, Mojmír, Kuthan, Josef
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 1992; Royal Society of Chemistry
• Subjects: Chemistry; Chemistry, Organic; Chemistry, Physical; Exact sciences and technology; Heterocyclic compounds; Heterocyclic compounds with o, s, se, te hetero atom and condensed derivatives; Organic chemistry; Physical Sciences; Preparations and properties; Science & Technology; THIABENZENES; CORRELATION SPECTROSCOPY; COHERENCE-TRANSFER; Sulfur heterocycle; Photochromism; Preparation; Pyran derivatives; NMR spectrometry; Spectral analysis; Absorption spectrum
• ISSN: 0300-9580; 1472-779X; 1364-5471
• DOI: 10.1039/P29920001301

1,3,3,5-Tetraarylpentane-1,5-diones 2 and 5 react with tetraphosphodecasulfide in xylene at elevated temperature to give the corresponding 2,4,4,6-tetraaryl-4H-thiopyrans 4 and 7. The mechanism of this transformation involves a fast initial step of dehydration of 2 and 5 to 2,4,4,6-tetraaryl-4H-pyrans 3, followed by a slower transformation to the 4H-thiopyran analogues 4. Using 2D NMR techniques, a complete assignment of the H-1 and C-13 NMR spectra of the 1-oxide and 1,1-dioxide analogues of 4 (1, X = SO and SO2) as well as of compounds 3c, j, l, m, 4a-m, 6 (the pyran analogue of 7) and 7 has been carried out. Compounds 4 and 7 undergo a reversible photochemical colour change after UV illumination. The maxima of the new absorption bands are situated at 540-660 nm. The non-exponential time dependence of the photodecolouration of 4a in the solid state is analysed in terms of dispersive first-order reaction kinetics. Dioxygen accelerates the decolouration process; the half-life at 299 K lies between 6600 s in air and several days in a vacuum (10(-3) Pa). The trapping of photoproducts 10a, 10e and 11a enables us to postulate the whole photolysis sequence.