Diazocines, bridged azobenzenes, exhibit superior photophysical properties compared to parent azobenzenes such as high switching efficiencies, quantum yields, and particularly switching wavelengths in the visible range. Synthesis, however, proceeds with low yields, and derivatives are difficult to prepare. We now present two heterodiazocines which are easier to synthesize, and the general procedures should also provide facile access to derivatives. Moreover, both compounds can be switched with light in the far-red (650 nm). Accessibility and photophysical properties make them ideal candidates for applications such as photoswitchable drugs and functional materials.

Diazocines are bridged azobenzenes with superior photophysical properties. In contrast to azobenzenes the Z configuration is thermodynamically stable and the E isomer is metastable. We present a new class of nitrogen bridged diazocines with bathochromically shifted switching wavelengths and remarkably high quantum yields (−NH–CH2− bridged diazocine: ΦZ→E = 0.57, ΦE→Z = 0.8). Z to E isomerization is induced by irradiation with blue light, whereas switching back to the Z isomer is accomplished with light in the near-infrared window (up to 740 nm), which is important for medical applications like photopharmacology (deep tissue penetration). Furthermore, substitution at the bridging nitrogen should provide access to widely applicable tricyclic, photoswitchable pharmacophores. The −NAc–CH2− bridged derivative is soluble in water, and all photophysical properties (conversion rates, quantum yields, and thermal half-lives) are largely retained. Hence, this diazocine is an ideal photoswitch for applications in biochemical systems and in photopharmacology.

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We report on avery unusual case of surface catalysis involving azobenzenes in contact with aA u(111) surface.A rate acceleration of the cis-trans isomerization on gold up to af actor of 1300 compared to solution is observed. By using carefully designed molecular frameworks,t he electronic coupling to the surface can be systematically tuned. The isomerization kinetics of molecules with very weak coupling to the metal is similar to that found in solution. Fortheir counterparts with strong coupling,the relaxation rate is shown to depend on the spin-density distribution in the triplet states of the molecules.T his suggests that an intersystem crossing is involved in the relaxation process.A side from their impact on catalytic processes,t hese effects could be used to trigger reactions over long distances.

Aromaticity of photoexcited molecules is an important concept in organic chemistry. Its theory, Baird's rule for triplet aromaticity since 1972 gives the rationale of photoinduced conformational changes and photochemical reactivities of cyclic π-conjugated systems. However, it is still challenging to monitor the dynamic structural change induced by the excited-state aromaticity, particularly in condensed materials. Here we report direct structural observation of a molecular motion and a subsequent packing deformation accompanied by the excited-state aromaticity. Photoactive liquid crystal (LC) molecules featuring a π-expanded cyclooctatetraene core unit are orientationally ordered but loosely packed in a columnar LC phase, and therefore a photoinduced conformational planarization by the excited-state aromaticity has been successfully observed by time-resolved electron diffractometry and vibrational spectroscopy. The structural change took place in the vicinity of excited molecules, producing a twisted stacking structure. A nanoscale torque driven by the excited-state aromaticity can be used as the working mechanism of new photoresponsive materials.