A combined optical and EPR spectroscopy study: azobenzene-based biradicals as reversible molecular photoswitches.

Azobenzene compounds are known as versatile examples for photoswitchable systems because of their isomeric cis- and trans-configurations. The switching between these isomers can be reversibly controlled by light excitation. In this study we characterize two members of this class by joining the azobenzene moiety with each two paramagnetic nitroxide spin labels.

Modular Two-Step Approach for the Stereodivergent Synthesis of 1,3-Diamines with Three Continuous Stereocenters.

A two-step reaction sequence for the highly stereodivergent construction of 1,3-diamines with three continuous stereocenters is reported. This novel method enables the controlled synthesis of any given diastereomer of the 1,3-diamine scaffold from a simple set of starting materials in a highly modular manner. The disclosed approach is based on the reaction of an enamide with an in situ generated N-acylimine followed by a subsequent trapping of the generated intermediate with a suitable nucleophile.

A chiral analog of the bicyclic guanidine TBD: synthesis, structure and Brønsted base catalysis.

Starting from ()-β-phenylalanine, easily accessible by lipase-catalyzed kinetic resolution, a chiral triamine was assembled by a reductive amination and finally cyclized to form the title compound . In the crystals of the guanidinium benzoate salt the six membered rings of adopt conformations close to an envelope with the phenyl substituents in pseudo-axial positions. The unprotonated guanidine catalyzes Diels-Alder reactions of anthrones and maleimides (25-30% ee).

Self-Assembled Monolayers of Pseudo-C-Symmetric, Low-Band-Gap Areneoxazolethiolates on Gold Surfaces.

A series of three homologous arene[2,3-d]-oxazole-2-thiols (benzoxazole-2-thiol (BOxSH), naphthaleneoxazole-2-thiol (NOxSH), and anthraceneoxazole-2-thiol (AOxSH)) were deposited onto Au(111) to obtain surfaces suitable as injection layers for organic electronics. The guiding idea was that the increasingly extended conjugated system would lower the band gap of the films while the introduction of the annulated heteroaromatic ring would provide the opportunity for pseudosymmetric attachment of the sulfur anchor, what should lower the conformational freedom of the system. In fact, the annulation of the oxazole ring lowers the optical band gaps of the parent compounds to 3.