Reversible Photoswitching of Isolated Ionic Hemiindigos with Visible Light

Abstract

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.

Molecular photoswitches in aqueous environments

“…by NMR spectroscopy, could not be performed. By attaching more efficiently solubilizing substituents, [253][254][255] several HI derivatives could be investigated in pure water with no or little amounts of organic co-solvents (2% (v/v) EtOH or 10% (v/v) DMSO). The PSD Z-E was around 80%E and back-isomerization was close to quantitative.…”

“…Thus, lipophilic crosslinkers can be used, as long as the protein can tolerate the required amounts of organic co-solvent. 254,789 The latter is very target-dependent and, unfortunately, not feasible for some proteins. In these cases, water-soluble photoswitches need to be applied to avoid, for instance, aggregation of the construct.…”

Proton‐Gated Ring‐Closure of a Negative Photochromic Azulene‐Based Diarylethene

“…Stimuli‐responsive molecules are the basis of information processing in biological as well as synthetic complex systems. Among them, photochromic molecules are particularly attractive for the ability to convert between (at least) two states by noninvasive and rapid optical stimuli with a potential of high spatial and temporal resolution . Additionally, multiple photochromic molecules have been developed, which in addition to light respond to a secondary stimulus, such as the presence of ions, oxidants/reductants, or acids/bases .…”

Protonenvermittelter Ringschluss eines negativ photochromen, Azulen‐basierten Diarylethens

“…Auf Stimuli reagierende Moleküle sind die Grundlage der Informationsverarbeitung in biologischen wie auch synthetischen, komplexen Systemen. Unter ihnen sind photochrome Moleküle aufgrund ihrer Fähigkeit zur Umwandlung zwischen (mindestens) zwei Zuständen durch nicht‐invasive und schnelle optische Stimuli bei gleichzeitig potentiell hoher räumlicher und zeitlicher Auflösung besonders attraktiv . Darüber hinaus wurden photochrome Moleküle entwickelt, die zusätzlich zu Licht auf einen sekundären Stimulus reagieren, beispielsweise auf die Anwesenheit von Ionen, Oxidations‐/Reduktionsmitteln, oder Säuren/Basen .…”