Photochemical Z→E Isomerization of a Hemithioindigo/Hemistilbene ω‐Amino Acid

Abstract

The molecule HTI, which combines hemithioindigo and hemistilbene molecular parts, allows reversible switching between two isomeric states. Photochromic behaviour of the HTI molecule is observed by irradiation with UV/Vis light. The photochemical reaction, a Z/E isomerization around the central double bond connecting the two molecular parts, is investigated by transient absorption and emission spectroscopy. For a special HTI molecule, namely, an omega-amino acid, the Z-->E isomerization process occurs on a timescale of 30 ps. In the course of the reaction fast processes on the 1-10 ps timescale are observed which point to motions of the molecule on the potential-energy surface of the excited state. The combination of transient absorption experiments in the visible spectral range with time-resolved fluorescence and infrared measurements reveal a photochemical pathway with three intermediate states. Together with a theoretical modelling procedure the experiments point to a sequential reaction scheme and give indications of the nature of the involved intermediates.

Light‐Switchable Peptides with a Hemithioindigo Unit: Peptide Design, Photochromism, and Optical Spectroscopy

“…Similar results were observed for other HTI‐based ω‐amino acid building blocks and the peptides shown in Table . Thermal E → Z isomerization reactions of HTI compounds (Table ) and peptides (Table ) determined in methanol by UV/Vis or 1 H NMR spectroscopy proceeded with a half‐life of >5 h, which allowed state‐specific isolation of inhibitor and peptide structures …”

“…The spectroscopic properties of HTI‐based photoswitches were established in recent years and a detailed reaction model of the molecular mechanism of the photochemical reactions Z → E and E → Z became available . This model describes both the reaction pathways and their intermediate states, and highlights an important feature of HTI: the ultrafast nature of the isomerization processes with a speed limit of about 1–2 ps that is triggered by near‐UV and visible light .…”

Flipping the Photoswitch: Ion Channels Under Light Control

“…Large changes in geometry and polarity, compatibility with two-photon excitation and fluorescence of the MC isomer make SPs attractive photochromes for biological applications Marriott et al 2008;Petchprayoon et al 2011). HTIs were synthesized and studied in detail recently (Figure 1c) (Cordes et al 2007;Eggers et al 2001;Herre 2005;Mostoslavskii 1970;Regner et al 2012). …”

Novel Chemical Tools to Study Ion Channel Biology

“…HTIs were synthesized and studied in detail recently (Fig. 1c) (Cordes et al 2007;Eggers et al 2001;Herre 2005;Mostoslavskii and Kravchenko 1970;Regner et al 2012). HTIs undergo light-induced isomerization from the thermodynamically favoured Z-isomer to the corresponding E-isomer and both isomers exhibit a planar structure.…”