Indigoid chromophores have emerged as versatile molecular photoswitches, offering efficient reversible photoisomerization upon exposure to visible light. Here we report synthesis of a new class of permanently charged hemiindigos (HIs) and characterization of photochemical properties in gas phase and solution. Gas-phase studies, which involve exposing mobility-selected ions in a tandem ion mobility mass spectrometer to tunable wavelength laser radiation, demonstrate that the isolated HI ions are photochromic and can be reversibly photoswitched between Z and E isomers. The Z and E isomers have distinct photoisomerization response spectra with maxima separated by 40-80 nm, consistent with theoretical predictions for their absorption spectra. Solvation of the HI molecules in acetonitrile displaces the absorption bands to lower energy. Together, gas-phase action spectroscopy and solution NMR and UV/Vis absorption spectroscopy represent a powerful approach for studying the intrinsic photochemical properties of HI molecular switches.
Keywords: ion mobility; mass spectrometry; molecular switch; photochemistry; photochromism.
© 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.