Synthesis of rigid photoswitchable hemithioindigo ω-amino acids

The synthesis of novel N-Boc- and N-Fmoc protected hemithioindigo-based ω-amino acids is described. An approach to modulate the thermal stability of a hemithioindigo subunit is presented. Placing the amino-group in the stilbene part from the para- to meta-position leads to an increase of the half-life of the thermally labile E-form from 19 h to 47 h.     

Effects of π-extension on pyrrole hemithioindigo photoswitches

The most red-shifted hemithioindigo photoswitches have been identified through systematic introduction of aryl units to a parent pyrrole hemithioindigo photoswitch. Increasing the size of the 5′-aryl substituent is ineffective at producing further redshifted chromophores. A second generation of 3′,5′-diarylated photoswitches which possess increased tunability is reported. Experimental and computational evidence indicates the 4′ position is electronically isolated from the bulk of the conjugated system.     

An unexpected triethylsilane-triggered rearrangement of thioaurones to thioflavonols under SPPS conditions

Thioaurones are converted to a mixture of thiaindenes and thioflavonols when exposed to reaction conditions employed in SPPS, that is, treatment with trifluoroacetic acid in the presence of triethylsilane.     

Active and Unidirectional Acceleration of Biaryl Rotation by a Molecular Motor

Light-driven molecular motors possess immense potential as central driving units for future nanotechnology. Integration into larger molecular setups and transduction of their mechanical motions represents the current frontier of research. Herein we report on an integrated molecular machine setup allowing the transmission of potential energy from a motor unit onto a remote receiving entity. The setup consists of a motor unit connected covalently to a distant and sterically encumbered biaryl receiver. By action of the motor unit, single-bond rotation of the receiver is strongly accelerated and forced to proceed unidirectionally. The transmitted potential energy is directly measured as the extent to which energy degeneration is lifted in the thermal atropisomerization of this biaryl. Energy degeneracy is reduced by more than 1.5 kcal mol⁻¹, and rate accelerations of several orders of magnitude in terms of the rate constants are achieved.     

Novel photoinduced cyclization of pentafluorophenylhemithioindigo

Photoirradiation of the pentafluorophenyl-substituted Z-hemithioindigo 1 causes a novel type of photoinduced cyclization, to produce the intramolecularly cyclized alcohol 2 and its dehydrated ether 3. For this photoinduced cyclization, the o-fluorine atoms of the phenyl group of 1 are found to be crucial.     

Direct Observation of Hemithioindigo‐Motor Unidirectionality

Hemithioindigo molecular motors undergo very fast unidirectional rotation upon irradiation with visible light, which has prevented a complete analysis of their working mechanism. In this work, we have considerably slowed down their motion by using a new synthesis for sterically hindered motor derivatives. This method allowed the first observation of all four intermediate states populated during rotation. The exact order in which each isomeric state is formed under irradiation conditions was elucidated using low temperature ¹H NMR spectroscopy in conjunction with other analytical methods. At the same time, complete unidirectionality could also be directly shown. Access to slowly rotating hemithioindigo motors opens up a plethora of new applications for visible‐light‐induced unidirectional motions, especially in areas such as catalysis, smart materials, and supramolecular chemistry.