LAboratoire de Spectrochimie Infrarouge et Raman – UMR 8516
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Séminaire du Pr. Yasushi Yokoyama

Yokohama National University, Department of Advanced Materials Chemistry, Graduate School of Engineering, Japan
Novel and high-performance photochromism based on 6π-electrocyclization

Photochromism based on 6π-electrocyclization generates two stereogenic sp3 carbon atoms when the hexatriene closes in a conrotatory manner to afford the cyclohexadiene by photoirradiation. A chiral factor introduced near the hexatriene moiety may control the conformation of the hexatriene, causing diasteroselective ring closure. This conformation control may also facilitate the ring closure, i.e. enlargement of the quantum yield of the photocyclization. This will be discussed at the outset of my talk. In one particular case of 1-(t-butyl)-2,3-bisthiazolyl-1-indenol, ring closure occurred with 100% diastereoselectivity and up to 85% cyclization quantum yield in hexane.

Control of hexatriene conformation with the chiral substituent thus proved to generate a set of diastereomers. On the other hand, if the chiral factor is applied to the photochromic molecule from the outside, then photocyclization produces a set of enantiomers as a chiral non-racemic mixture. This will be my next subject of discussion in which the chiral source is the hydrophobic pocket of a biological molecule, human serum albumin, dissolved in buffer solution. The enantiomer excess is up to 60% upon photoirradiation.

Finally, I would like to explain the on/off switching of fluorescence in water-rich solutions applicable to biological systems. When this compound has a pH-sensitive site, the fluorescence can then be modulated by the pH of the solution.

Y. Yokoyama, T. Shiozawa, Y. Tani, T. Ubukata, Angew. Chem. Int. Ed., 2009, 48, 4521.
S. Delbaere, J. Berthet, T. Shiozawa, Y. Yokoyama, J. Org. Chem., 2012, in press.
T. Shiozawa, M. K. Hossain, T. Ubukata, Y. Yokoyama, Chem. Commun., 2010, 46, 4785.
K. Morinaka, T. Ubukata, Y. Yokoyama, Org. Lett., 2009, 11, 3890. Synfacts, 2009, 11, 1217.
K. Suzuki, T. Ubukata, Y. Yokoyama, Chem. Commun., 2012, 48, 765.

The seminar will be held on 21.02.2012 at 14h00
LASIR meeting room, basement building C5