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

• ring, so-called arylazopyrazoles, which have excellent potential against the current state of the art (Figure 1b) [17][18]. Specifically, arylazopyrazole 4pzMe can be near quantitatively (>98%) photoswitched in both directions, and 4pzH demonstrated an exceptionally long thermal Z-isomer half-life

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

• Arylazopyrazoles represent a new family of molecular photoswitches characterized by a near-quantitative conversion between two states and long thermal half-lives of the metastable state. Here, we investigated the behavior of a model arylazopyrazole in the presence of a self-assembled cage based on Pd–imidazole

• green light and resulted in the initial 1:2 cage/E-arylazopyrazole complex. This back-isomerization reaction also proceeded in the dark, with a rate significantly higher than in the absence of the cage. Keywords: arylazopyrazoles; coordination cages; inclusion complexes; molecular switches

• ]. Among them, arylazopyrazoles have attracted considerable interest because of their synthetic availability and desirable photochemical properties, such as the high thermal stability of the Z isomer and a large band separation between the E and Z isomers, allowing each to be addressed with a high

Reversible end-to-end assembly of selectively functionalized gold nanorods by light-responsive arylazopyrazole–cyclodextrin interaction

• Maximilian Niehues,
• Patricia Tegeder and
• Bart Jan Ravoo

Beilstein J. Org. Chem. 2019, 15, 1407–1415, doi:10.3762/bjoc.15.140

• sonication, whilst some dimers could not be fully dispersed. Possibly this observation can be explained from the limited photostationary states (PSS) of azobenzenes (E – Z: 80%, Z – E: 70%) [36]. Arylazopyrazoles (AAP) are a new class of molecular switches introduced by Fuchter et al. with excellent

• light-responsive interaction between arylazopyrazoles and β-CD for the end-to-end assembly of AuNR. The substitution of azobenzenes by AAP as guest molecules, which feature nearly quantitative photostationary states, allows the control over assembled and disassembled states solely by irradiation. The

• reversibly be shifted back and forth ending at the original wavelength. Switching of the end-to-end assembly was possible over four cycles without fatigue appearance. Previously reported limited feasibilities of azobenzenes could be resolved by the implementation of arylazopyrazoles. This report shows a

Superstructures with cyclodextrins: Chemistry and applications IV

• Gerhard Wenz

Beilstein J. Org. Chem. 2017, 13, 2157–2159, doi:10.3762/bjoc.13.215

• ]. The group of Ravoo also conjugated arylazopyrazoles to amphiphilic cyclodextrin derivatives that form vesicles triggered by light [17]. A star-shaped polycationic CD derivative with many breakable, intrinsic, disulfide linkages forms nanoparticles with messenger RNA and drugs and is particularly

Approaches towards the synthesis of 5-aminopyrazoles

• Ranjana Aggarwal,
• Vinod Kumar,
• Rajiv Kumar and
• Shiv P. Singh

Beilstein J. Org. Chem. 2011, 7, 179–197, doi:10.3762/bjoc.7.25

• coupling with aromatic diazonium salts gave the corresponding 2-arylhydrazones 47, which on treatment with hydrazine hydrate formed the 5-amino-4-arylazopyrazoles 48. 3-Oxo-3-(pyrrol-2-yl)propanenitrile (16) reacted with trichloroacetonitrile to yield enamine 49, which on further treatment with hydrazine