Isomerisation of an intramolecular hydrogen-bonded photoswitch: protonated azobis(2-imidazole). Issue 20 (9th May 2017)

• Record Type: Journal Article
• Authors: Bull, James N.; Scholz, Michael S.; Coughlan, Neville J. A.; Bieske, Evan J.
• Is Part Of: Physical chemistry chemical physics. Volume 19:Issue 20(2017)
• Page Start: 12776
• Page End: 12783
• Publication Date: 2017-05-09
• Subjects: Chemistry, Physical and theoretical -- Periodicals; 541.3
• DOI: 10.1039/c7cp01733b
• Languages: English
• ISSNs: 1463-9076

Abstract

Abstract : Reversible E – Z photoswitching of a protonated azoheteroarene is demonstrated using ion mobility mass spectrometry. 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 E – Z photoisomerisation occurring over the 360–520 nm range (peak at 460 nm), and Z – E 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.