Hannover 2010 – scientific programme

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MO: Fachverband Molekülphysik

MO 25: Poster: Photochemistry

MO 25.1: Poster

Thursday, March 11, 2010, 16:00–18:30, Lichthof

The ultrafast photochemistry of 6,8-dinitro-BIPS: Isomers, Isomerization and Ring-closure — •Johannes Buback, Martin Kullmann, Florian Langhojer, and Tobias Brixner — Institut für Physikalische Chemie, Universität Würzburg, 97074 Würzburg

The 6,8-dinitro-BIPS (1',3'-dihydro-1',3',3'-trimethyl-6,8-dinitrospiro-[2H-1-benzopyran-2,2'-(2H)-indole]) is a candidate for an electrocyclic molecular switch on spiropyran basis. While the ground state of other substitution patterns is the ring-closed spiropyran isomer, the thermal equilibrium of the 6,8-dinitro-BIPS is shifted to the into ring-open merocyanine. Due to the cis-trans-configuration of the methin bridge connecting the two chromophores several stereoisomers may exist in solution.

We have carried out spectrally resolved transient absorption experiments in the ultraviolet, visible and mid-infrared regime on 6,8-dinitro-BIPS in chloroform with femtosecond time resolution showing ultrafast photoreactions after the excitation. The visible pump pulses were varied from 545 nm to 650 nm resulting in different bleach and recovery behaviour while probing in the visible regime. The spectral structure of the permanent bleach and a temporal analysis of the transient data reveal at least two processes taking place on a picosecond timescale. These can be associated with different merocyanine structures present in solution which perform ring-closure or isomerization processes.