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Issue 44, 2018
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How a linear triazene photoisomerizes in a volume-conserving fashion

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Understanding deactivation mechanisms of functional groups is a key step to design novel photo-active devices and molecular imaging agents. Here, we elucidate the photochemistry of linear triazenes, an extended analogue of the photo-switchable azo group, exemplarily for the widely used DNA-minor-groove binder berenil. Combining ultrafast spectroscopy and ab initio calculations unveils that the E-azo,s-trans structure of berenil predominates in the gas phase and in aqueous solution, and ADC(2) intrinsic reaction coordinate calculations disclose that the excited-state relaxation to the S1 minima/conical intersections follows a two-step mechanism: N[double bond, length as m-dash]N bond stretching followed by a bicycle-pedal rotation in the triazene bridge. Furthermore, studying the ground-state pathways shows that a fraction of the molecules relaxes back to the E-azo,s-trans isomer while the other part photoisomerizes to the Z-azo,s-trans via a hula-twist motion, as evidenced by experimental quantum yields of Φ ≈ 0.5 found for berenil in water, ethylene glycol, or bound to β-trypsin. Moreover, our studies show that while the excited-state relaxation is insensitive to the environment, the ground-state dynamics depend on biomolecular binding partners.

Graphical abstract: How a linear triazene photoisomerizes in a volume-conserving fashion

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The article was received on 15 Aug 2018, accepted on 24 Oct 2018 and first published on 25 Oct 2018

Article type: Paper
DOI: 10.1039/C8CP05208E
Citation: Phys. Chem. Chem. Phys., 2018,20, 28075-28087

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    How a linear triazene photoisomerizes in a volume-conserving fashion

    A. Marefat Khah, L. Grimmelsmann, J. Knorr, P. Nuernberger and C. Hättig, Phys. Chem. Chem. Phys., 2018, 20, 28075
    DOI: 10.1039/C8CP05208E

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