Photochromic derivatives of indigo: historical overview of development, challenges and applications

• Gökhan Kaplan,
• Zeynel Seferoğlu and
• Daria V. Berdnikova

Beilstein J. Org. Chem. 2024, 20, 228–242, doi:10.3762/bjoc.20.23

• incorporating redox-active tetrathiafulvalene (TTF) residues (Figure 7), known for their ability to form intramolecular π-dimers upon two-electron oxidation [47]. Thus, upon irradiation of the oxidized molecule 24 with 660 nm light, the thermal half-life of the Z-isomer exhibited a significant increase

• compounds [66]. It was shown that despite the prerequisites for the occurrence of the excited-state proton transfer, monoarylated indigos underwent E–Z photoisomerization upon red-light irradiation at 625 nm. Remarkably, the thermal half-life of the Z-isomer of compound 20b was sensitive to the presence of

• unsymmetrical indigo derivatives 22 bearing a –CH2Boc as N'-alkyl group and various N-aryl groups [42]. It was found that the electronic effect of the para-substituents in the N-aryl pendants had a crucial influence on the thermal half-life of the photoinduced Z-isomers. Thus, the electron-withdrawing groups

Potent hemithioindigo-based antimitotics photocontrol the microtubule cytoskeleton in cellulo

• Alexander Sailer,
• Franziska Ermer,
• Yvonne Kraus,
• Rebekkah Bingham,
• Ferdinand H. Lutter,
• Julia Ahlfeld and
• Oliver Thorn-Seshold

Beilstein J. Org. Chem. 2020, 16, 125–134, doi:10.3762/bjoc.16.14

• photoswitching (λ = 450 nm for Z → E and 530 nm for E → Z switching), with the high fatigue resistance characteristic of HTIs. The E-isomer's thermal half-life in EtOAc or DMSO was ca. 40 s (Figure 3 and Supporting Information File 1, Figure S3). Its absorption spectra and photoswitchability were unaltered by

Design, synthesis and investigation of water-soluble hemi-indigo photoswitches for bioapplications

• Daria V. Berdnikova

Beilstein J. Org. Chem. 2019, 15, 2822–2829, doi:10.3762/bjoc.15.275

• the absorption maxima of the Z- and E-forms. At the same time, the introduction of the second methoxy group to the phenyl ring resulted in a decrease of the Z–E isomerization quantum yield and reduced the thermal half-life of E-1c in comparison to E-1b (Table 1). Nevertheless, the dimethoxy

Chemical tuning of photoswitchable azobenzenes: a photopharmacological case study using nicotinic transmission

• Lorenzo Sansalone,
• Jun Zhao,
• Matthew T. Richers and
• Graham C. R. Ellis-Davies

Beilstein J. Org. Chem. 2019, 15, 2812–2821, doi:10.3762/bjoc.15.274

• the cis-4FAB configuration (thermal half-life > 12 days at 37 °C in physiological buffer) and cis–trans photostationary states above 84%. Furthermore, the well-separated n–π* absorption bands of trans- and cis-4FAB allow facile photoswitching with visible light in two optical channels. A convergent 11

• such regular AB photoprobes. We have developed a synthetic route that allows the production of asymmetrically substituted 4FAB photoprobes (1 and 2, Scheme 1). Importantly, the cis and trans PSS are both >84%, and the thermal half-life of the cis configuration is 12 days in physiological buffer and

• tolerate such strong electron-donating group. Hecht and co-workers had shown in their original paper that two amides connected to 2FAB and 4FAB via nitrogen atoms also lost much of the excellent features of the parent 4FAB chromophore [12]. (Note, "1FAB" also has a very short thermal half-life of the cis

A combinatorial approach to improving the performance of azoarene photoswitches

• Joaquin Calbo,
• Aditya R. Thawani,
• Rosina S. L. Gibson,
• Andrew J. P. White and
• Matthew J. Fuchter

Beilstein J. Org. Chem. 2019, 15, 2753–2764, doi:10.3762/bjoc.15.266

• measurements of representative examples, we demonstrate that ortho-benzene substitution of the arylazopyrazoles drastically increases the Z-isomer stability and allows further tuning of their addressability. This includes the discovery of new azopyrazoles with a Z-isomer thermal half-life of ≈46 years. Such

• results therefore define improved designs for high performance azo switches, which will allow for high precision optically addressable applications using such components. Keywords: arylazopyrazoles; azobenzenes; molecular switches; ortho-substitution; photoswitches; thermal half-life; Introduction

• demonstrate slow thermal Z–E relaxation and the potential to switch with red light, while the o-fluoro compounds reported by Hecht and co-workers [13][14] offer excellent two-way isomerization with visible light and the longest thermal half-life reported for an azobenzene molecule (≈700 days at 25 °C) to date

Reversible switching of arylazopyrazole within a metal–organic cage

• Anton I. Hanopolskyi,
• Soumen De,
• Michał J. Białek,
• Yael Diskin-Posner,
• Liat Avram,
• Moran Feller and
• Rafal Klajn

Beilstein J. Org. Chem. 2019, 15, 2398–2407, doi:10.3762/bjoc.15.232

• linear profile of the recovery suggests that the reaction obeys first-order kinetics, with a rate constant of 0.0975 h−1, corresponding to a thermal half-life of Z-1, τ1/2 ≈ 7.1 hours. This value of τ1/2 is surprisingly small vis-à-vis the previously reported [35] τ1/2 ≈ 10 days in acetonitrile. To

Fluorinated azobenzenes as supramolecular halogen-bonding building blocks

• Esther Nieland,
• Oliver Weingart and
• Bernd M. Schmidt

Beilstein J. Org. Chem. 2019, 15, 2013–2019, doi:10.3762/bjoc.15.197

• significantly strengthened in solution. However, the bathochromic shift of the π→π* band leads to a partial overlap with the n→π* band, making it slightly more difficult to address. The introduction of iodine substituents is furthermore accompanied with a diminishing thermal half-life. A series of three

• . However, most importantly, the azobenzenes still can be conveniently handled at room temperature with a half-life of at least a working day, allowing for studying both states of the systems without needs for in situ irradiation (the thermal half-life of A3 at room temperature is 14.98 hours in MeCN, see

• iodoethynyl group, as trade-off, photophysical properties are changing. The bathochromic shift of the π→π* band leads to an overlap with the n→π* excitation, making it more difficult to address, together with a diminishing thermal half-life. Both effects can be qualitatively reproduced and understood with the

Azologization of serotonin 5-HT₃ receptor antagonists

• Karin Rustler,
• Galyna Maleeva,
• Piotr Bregestovski and
• Burkhard König

Beilstein J. Org. Chem. 2019, 15, 780–788, doi:10.3762/bjoc.15.74

• with a thermal half-life in the seconds to minutes range, the azo-extended compounds 23 and 28 showed only slow thermal back-isomerization (day range) at room temperature. Depending on the desired application, both properties may be of benefit. For thermally instable compounds, only one wavelength for

London dispersion as important factor for the stabilization of (Z)-azobenzenes in the presence of hydrogen bonding

• Andreas H. Heindl,
• Raffael C. Wende and
• Hermann A. Wegner

Beilstein J. Org. Chem. 2018, 14, 1238–1243, doi:10.3762/bjoc.14.106

• unneglectable stabilizing element in controlling interactions in functionalized molecules. During studies on cyclobisazodiphenylmethane [18] we noticed that the bulky (Z)-4,4’-bis[4-(3,5,5-trimethylhexanoylamino)benzyl]azobenzene (4, Scheme 2a) showed an unexpectedly increased thermal half-life compared to

Amino-substituted diazocines as pincer-type photochromic switches

• Hanno Sell,
• Christian Näther and
• Rainer Herges

Beilstein J. Org. Chem. 2013, 9, 1–7, doi:10.3762/bjoc.9.1

• thermal half-life of the trans isomer, however, is drastically increased (3,3’-diamino-EBAB 4: 74 h, 3,3’-diacetamido-EBAB 5: 46 h). The EBAB derivatives upon photoisomerization perform a pincer-like motion. Diacetamido derivative 5 binds ethylenediamine better in its cis (closed) form than in its trans

Design and synthesis of a photoswitchable guanidine catalyst

• Philipp Viehmann and
• Stefan Hecht

Beilstein J. Org. Chem. 2012, 8, 1825–1830, doi:10.3762/bjoc.8.209

• rate law, the rate constant of the thermal Z→E isomerization at 40 °C was determined to be k(40 °C) = 6.3·10−5 s−1 corresponding to a half-life of τ1/2 = 3 h. The measurement at slightly elevated temperature (40 °C) was necessary since at 25 °C the thermal half-life increases significantly (Supporting

• Information File 1, Figure S-5), leading to distinct difficulties in its determination, e.g., the evaporation of the solvent and the resulting change in concentration. Therefore, the rate constant and thermal half-life at 25 °C could only be estimated by using data points from the first 36 h (Supporting