Iminothioindoxyl as a molecular photoswitch with 100\u2009nm band separation in the visible range

Mark W H Hoorens,Wiktor Szymanski,Mariangela Di Donato,Laura Slappendel,Ben L Feringa,Wybren Jan Buma,Michiel Hilbers,Samuele Fanetti,Miroslav Medved’,Adèle D Laurent

doi:10.1038/s41467-019-10251-8

Abstract

Light is an exceptional external stimulus for establishing precise control over the properties and functions of chemical and biological systems, which is enabled through the use of molecular photoswitches. Ideal photoswitches are operated with visible light only, show large separation of absorption bands and are functional in various solvents including water, posing an unmet challenge. Here we show a class of fully-visible-light-operated molecular photoswitches, Iminothioindoxyls (ITIs) that meet these requirements. ITIs show a band separation of over 100 nm, isomerize on picosecond time scale and thermally relax on millisecond time scale. Using a combination of advanced spectroscopic and computational techniques, we provide the rationale for the switching behavior of ITIs and the influence of structural modifications and environment, including aqueous solution, on their photochemical properties. This research paves the way for the development of improved photo-controlled systems for a wide variety of applications that require fast responsive functions.

Highlights

Light is an exceptional external stimulus for establishing precise control over the properties and functions of chemical and biological systems, which is enabled through the use of molecular photoswitches
In our continuous efforts to expand the limited repertoire of molecular photoswitches, we further focused on several characteristics that they should possess, besides the visible light operation with large band separation
For application in biological systems, new and improved switches are needed. This is underlined e.g. by a recent report by the group of Thorn-Seshold[48], in which the first HTI-based photo-controlled pharmacophore was reported. This study demonstrates both the potential of indigoid-based photoswitches as well as the need for improved band separation of photo-isomers and improved water solubility

Summary

Introduction

Light is an exceptional external stimulus for establishing precise control over the properties and functions of chemical and biological systems, which is enabled through the use of molecular photoswitches. For switches that can be operated in both directions in the visible range, such as substituted azobenzenes[1] and indigoids such as indigo[20] and hemithioindigos[21,22], the band separation becomes a challenge, limiting their selective bidirectional photoisomerization. Recently, this problem has been addressed for azobenzenes by the groups of Woolley and Hecht, who developed fully-visible-light-responsive azobenzenes[1,3,23], which - despite lower water solubility and challenging synthesis - have been successfully used for biological applications[24,25,26]. We demonstrate that these spectacular photochemical properties are retained for aqueous solutions, which opens opportunities for applying ITI for reversibly controlling biological systems

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Conclusion