Dresden 2011 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 34: Photochemistry

MO 34.2: Vortrag

Freitag, 18. März 2011, 10:45–11:00, TOE 317

Control of the dissociation of diphenylallyl derivatives — •Michael Mikhailov¹, Igor Pugliesi¹, Konstantin Troshin², Herbert Mayr², and Eberhard Riedle¹ — ¹LS BioMolekulare Optik, LMU München — ²AK Mayr, Dept. Chemie, LMU München

We study the photodissociation of the model system (E)-1,3-diphenylallyl acetate (H-H-OAc) using broadband fs spectroscopy. After UV excitation H-H-OAc undergoes simultaneous homolysis and heterolysis to form (1,3-diphenylallyl)^• and (1,3-diphenylallyl)⁺. The formation of the same products is also observed for two asymmetrically substituted isomers of the model compound: (E)-1-(3,5-difluorophenyl)-3-p-tolylallyl acetate (Me-mFF-OAc), where the methyl electron-donating substituent is attached to the styrene part and the electron-withdrawing fluorine substituents to the toluene part, and (E)-3-(3,5-difluorophenyl)-1-p-tolylallyl acetate (mFF-Me-OAc), where the substitution is reversed. While the bond cleavage is similar to H-H-OAc, the reaction rates are significantly different: 24.2 ps and 96.3 ps for the cation and radical rise and decay times of Me-mFF-OAc, and 190 ps and about 9 ns for the cation and radical rise and decay times of mFF-Me-OAc. The observed difference can be explained by the fact, that attaching the electron donating methyl substituent to the styrene part stabilizes the cation and radical of Me-mFF-OAc, whereas destabilization of the styrene part takes place for mFF-Me-OAc due to the electron withdrawing fluorines. Thus, a control over the photoinduced bond cleavage rates can be achieved by the substituent change.