title: Making fast photoswitches faster--using Hammett analysis to understand the limit of donor-acceptor approaches for faster hemithioindigo photoswitches.
abstract: Hemithioindigo (HTI) photoswitches have a tremendous potential for biological and supramolecular applications due to their absorptions in the visible-light region in conjunction with ultrafast photoisomerization and high thermal bistability. Rational tailoring of the photophysical properties for a specific application is the key to exploit the full potential of HTIs as photoswitching tools. Herein we use time-resolved absorption spectroscopy and Hammett analysis to discover an unexpected principal limit to the photoisomerization rate for donor-substituted HTIs. By using stationary absorption and fluorescence measurements in combination with theoretical investigations, we offer a detailed mechanistic explanation for the observed rate limit. An alternative way of approaching and possibly even exceeding the maximum rate by multiple donor substitution is demonstrated, which give access to the fastest HTI photoswitch reported to date.
authors.affiliation: Institute for BioMolecular Optics, Ludwig-Maximilians-University Munich, Oettingenstr. 67, 80538 Munich (Germany).
authors.forename: Benjamin
authors.initials: B
authors.lastname: Maerz
authors.forename: Sandra
authors.initials: S
authors.lastname: Wiedbrauk
authors.forename: Sven
authors.initials: S
authors.lastname: Oesterling
authors.forename: Elena
authors.initials: E
authors.lastname: Samoylova
authors.forename: Artur
authors.initials: A
authors.lastname: Nenov
authors.forename: Peter
authors.initials: P
authors.lastname: Mayer
authors.forename: Regina
authors.initials: R
authors.lastname: de Vivie-Riedle
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Zinth
authors.forename: Henry
authors.initials: H
authors.lastname: Dube
mesh_terms: D005453:Fluorescence; D007203:Indigo Carmine / Q000031:analogs & derivatives* / Q000737:chemistry; D007536:Isomerism; D008027:Light; D008958:Models, Molecular; D055668:Photochemical Processes; D010777:Photochemistry; D013057:Spectrum Analysis
chemical_list: C527420:hemithioindigo; D007203:Indigo Carmine
keywords: ab initio calculations; isomerization; photochemistry; photochromism; time-resolved spectroscopy