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Issue 20, 2017
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Isomerisation of an intramolecular hydrogen-bonded photoswitch: protonated azobis(2-imidazole)

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Abstract

Photoisomerisation of protonated azobis(2-imidazole), an intramolecular hydrogen-bonded azoheteroarene photoswitch molecule, is investigated in the gas phase using tandem ion mobility mass spectrometry. The E and Z isomers exhibit distinct spectral responses, with EZ photoisomerisation occurring over the 360–520 nm range (peak at 460 nm), and ZE photoisomerisation taking place over the 320–420 nm range (peak at 390 nm). A minor photodissociation channel involving loss of N2 is observed for the E-isomer with a maximum efficiency at 390 nm, blue-shifted by ≈70 nm relative to the wavelength for maximum photoisomerisation response. Loss of N2 is also the predominant collision-induced dissociation channel. Electronic structure calculations suggest that E-isomer photoisomerisation involves S1(ππ*) excitation, whereas the Z-isomer photoisomerisation involves S2(ππ*) excitation. Conversion between the E and Z isomers through collisional excitation, which is calculated to occur through both inversion and torsion pathways, is investigated experimentally by colliding the molecular ions with nitrogen buffer gas over a range of electric fields. This study demonstrates the versatility of tandem ion mobility mass spectrometry for exploring the isomerisation of molecular photoswitches initiated by either light or collisions.

Graphical abstract: Isomerisation of an intramolecular hydrogen-bonded photoswitch: protonated azobis(2-imidazole)

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Publication details

The article was received on 18 Mar 2017, accepted on 27 Apr 2017 and first published on 02 May 2017


Article type: Paper
DOI: 10.1039/C7CP01733B
Citation: Phys. Chem. Chem. Phys., 2017,19, 12776-12783
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    Isomerisation of an intramolecular hydrogen-bonded photoswitch: protonated azobis(2-imidazole)

    J. N. Bull, M. S. Scholz, N. J. A. Coughlan and E. J. Bieske, Phys. Chem. Chem. Phys., 2017, 19, 12776
    DOI: 10.1039/C7CP01733B

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