γ-Amino Alcohols via Energy Transfer Enabled Brook Rearrangement.

In the long-standing quest to synthesize fundamental building blocks with key functional group motifs, photochemistry in the recent past has comprehensively established its attractiveness. Amino alcohols are not only functionally diverse but are ubiquitous in the biologically active realm of compounds. We developed bench-stable bifunctional reagents that could then access the sparsely reported γ-amino alcohols directly from feedstock alkenes through energy transfer (EnT) photocatalysis. A designed 1,3-linkage across alkenes is made possible by the intervention of a radical Brook rearrangement that takes place downstream to the EnT-mediated homolysis of our reagent(s). A combination of experimental mechanistic investigations and detailed computational studies (DFT) indicates a radical chain propagated reaction pathway.

Calamitic Liquid Crystals for Reversible Light-Modulated Phase Regulation Based on Arylazopyrazole Photoswitches.

The design of responsive liquid crystals enables a diversity of technological applications. Especially photochromic liquid crystals gained a lot of interest in recent years due to the excellent spatiotemporal control of their phase transitions. In this work we present calamitic light responsive mesogens based on a library of arylazopyrazole photoswitches. These compounds show liquid-crystalline behavior as shown by differential scanning calorimetry, grazing incidence X-ray diffraction and polarized optical microscopy. UV-vis spectroscopy and NMR analysis confirmed the excellent photophysical properties in solution and thin film. Additionally, polarized optical microscopy studies of the pristine compounds show reversible phase transition upon irradiation with light. Moreover, as a dopant in the commercially available liquid crystal 4-cyano-4'-pentylbiphenyl (5CB), the temperature range was reduced to ambient temperatures while preserving the photophysical properties. Remarkably, this co-assembled system shows reversible liquid-crystalline to isotropic phase transition upon irradiation with light of different wavelengths. The spatiotemporal control of the phase transition of the liquid crystals offers opportunities in the development of optical devices.

Calamitic Liquid Crystals for Reversible Light-Modulated Phase Regulation Based on Arylazopyrazole Photoswitches.

Invited for the cover of this issue are the groups of Kentaro Tanaka at Nagoya University and Bart Jan Ravoo at the University of Münster. The image depicts the photoisomerization of a mesogen upon irradiation with different wavelengths of light. Read the full text of the article at 10.1002/chem.202302958.

ortho-Selective Dearomative [2π + 2σ] Photocycloadditions of Bicyclic Aza-Arenes.

Dearomative photocycloadditions are valuable chemical transformations, serving as an efficient platform to create three-dimensional molecular complexity. However, the photolability of the original addition product especially within the context of ortho cycloadditions often causes undesired consecutive rearrangements, rendering these ortho cycloadducts elusive. Herein, we report an ortho-selective intermolecular photocycloaddition of bicyclic aza-arenes including (iso)quinolines, quinazolines, and quinoxalines by utilizing a strain-release approach. With bicyclo[1.1.0]butanes as coupling partners, this dearomative [2π + 2σ] cycloaddition enables the straightforward construction of C(sp3)-rich bicyclo[2.1.1]hexanes directly connected to N-heteroarenes. Photophysical experiments and DFT calculations revealed the origin of the [2π + 2σ] selectivity and indicate that, in addition to the originally proposed energy transfer or direct excitation pathways, a chain reaction mechanism is operative depending on the reaction conditions.