Hannover 2020 – scientific programme
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MO: Fachverband Molekülphysik
MO 10: Collisions and Reactions
MO 10.5: Talk
Wednesday, March 11, 2020, 12:00–12:15, f142
Z → E and E → Z Photoisomerization Dynamics of an Oxygen-Heterodiazocine upon S1(nπ*) Photoexcitation — •Dennis Bank1, Birthe Behr1, Falk Renth1, Melanie Hammerich2, Rainer Herges2, and Friedrich Temps1 — 1Institute of Physical Chemistry, Christian-Albrechts-University Kiel, Germany — 2Institute of Organic Chemistry, Christian-Albrechts-University Kiel, Germany
Heterodiazocines are a novel class of azobenzene-related photochromic molecules with an intramolecular bridge consisting a CH2-heteroatom linker group between their phenyl rings. This bridge initiates a steric tension that results in superior photophysical properties. We investigated the very efficient photo-induced isomerization ( ΦZ → E = 0.7 and ΦE → Z = 0.55) dynamics of 12H-dibenzo[b,f][1,4,5] oxadiazocine (ODz) by a combination of femtosecond time-resolved electronic absorption spectroscopy and ab initio quantum chemical calculations. After photoexcitation of the thermodynamically stable Zboat isomer at λ pump = 387 nm the populated S1 (nπ*) state deactivates within τ ≤ 150 fs. The subsequent complex ground-state dynamics of the Zboat → Etwist isomerization proceeds via formation of the vibrationally hot intermediate Echair species with τ = 3 ps and crossing of an energy barrier of E = 0.55 eV within τ = 15 ps. In contrast, the Etwist → Zboat photoisomerization upon excitation at λ pump = 530 nm is completed after only τ = 230 fs followed by vibrational cooling in the ground state with τ = 20 ps.