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Erlangen 2018 – wissenschaftliches Programm

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MO: Fachverband Molekülphysik

MO 4: Photochemistry

MO 4.3: Vortrag

Montag, 5. März 2018, 14:30–14:45, PA 1.150

Ultrafast Photoinduced dynamics of Benzocyclobutenedione in Solution — •Xiaonan Ma, Hans-Christian Schmitt, Michael Wenzel, Marco Flock, Ingo Fischer, Roland Mitrić, and Tobias Brixner — Institut für Physikalische und Theoretische Chemie, Universität Würzburg, Am Hubland, 97074 Würzburg

Benzocyclobutenedione (BCBD) has an abundant photochemistry and has been studied since decades, but its sub-ns photochemical dynamics remained unknown. In this work, the ultrafast photophysics and photochemistry of BCBD dissolved in dichloromethane was investigated by transient IR and UV/Vis absorption spectroscopy. The initial UV-populated S3 (ππ*) state deactivates rapidly to the S1 (nπ*) state via internal conversion (IC) followed by sub-ps vibrational relaxation (VR). In parallel, the S1 (υ>0) state BCBD decarbonylates to benzocyclopropenone, which subsequently rearranges to cyclopentadienylideneketene. Two extra reactions on the S1 (υ=0) state that compete with deactivation to S0 were identified by transient IR spectra combined with DFT/TDDFT calculations. Ring-opening in the S1 (υ=0) state produces vibrationally hot bisketene cools within 22 ps. This process competes with the intramolecular rearrangement to singlet oxacarbene and subsequent conversion into the triplet carbene via intersystem crossing (ISC). A long time product identified in the transient UV/Vis spectra is probably due to dimerization of the carbene. Molecular dynamics (MD) simulations of the early-time photochemistry of BCBD successfully reproduce the formation of benzocyclopropenone and oxacarbene.

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