We report on two regioisomeric, diazocine ligands 1 and 2 that can both be photoswitched between the E‐ and Z‐configurations with violet and green light. The self‐assembly of the four species (1‐Z, 1‐E, 2‐Z, 2‐E) with CoII ions was investigated upon changing the coordination vectors as a function of the ligand configuration (E vs Z) and regioisomer (1 vs 2). With 1‐Z, Co2(1‐Z)3 was self‐assembled, while a mixture of ill‐defined species (oligomers) was observed with 2‐Z. Upon photoswitching with 385 nm to the E configurations, the opposite was observed with 1‐E forming oligomers and 2‐E forming Co2(2‐E)3. Light‐controlled dis/assembly was demonstrated in a ligand competition experiment with sub‐stoichiometric amounts of CoII ions; alternating irradiation with violet and green light resulted in the reversible transformation between Co2(1‐Z)3 and Co2(2‐E)3 over multiple cycles without significant fatigue by photoswitching.

Photopharmacology is an emerging approach in drug design and pharmacological therapy. Light is used to switch a pharmacophore between a biologically inactive and an active isomer with high spatiotemporal resolution at the site of illness, thus potentially avoiding side effects in neighboring healthy tissue. The most frequently used strategy to design a photoswitchable drug is to replace a suitable functional group in a known bioactive molecule with azobenzene. Our strategy is different in that the photoswitch moiety is closer to the drug’s scaffold. Docking studies reveal a very high structural similarity of natural 17β-estradiol and the E isomers of dihydroxy diazocines, but not their Z isomers, respectively. Seven dihydroxy diazocines were synthesized and subjected to a biological estrogen reporter gene assay. Four derivatives exhibit distinct estrogenic activity after irradiation with violet light, which can be shut off with green light. Most remarkably, the photogenerated, active E form of one of the active compounds isomerizes back to the inactive Z form with a half-life of merely several milliseconds in water, but nevertheless is active for more than 3 h in the presence of the estrogen receptor. The results suggest a significant local impact of the ligand–receptor complex toward back-isomerization. Thus, drugs that are active when bound but lose their activity immediately after leaving the receptor could be of great pharmacological value because they strongly increase target specificity. Moreover, the drugs are released into the environment in their inactive form. The latter argument is particularly important for drugs that act as endocrine disruptors.

A set of dipolar molecular rotor compounds was designed, synthesized and adsorbed as self-assembled 2D arrays on Ag(111) surfaces. The title molecules are constructed from three building blocks: (a) 4,8,12-trioxatriangulene (TOTA) platforms that are known to physisorb on metal surfaces such as Au(111) and Ag( 111), (b) phenyl groups attached to the central carbon atom that function as pivot joints to reduce the barrier to rotation, (c) pyridine and pyridazine units as small dipolar units on top. Theoretical calculations and scanning tunneling microscopy (STM) investigations hint at the fact that the dipoles of neighboring rotors interact through space through pairs of energetically favorable head-to-tail arrangements.

Wir berichten über zwei regioisomere Diazocinliganden 1 und 2, die beide mit violettem und grünem Licht zwischen den E-und Z-Konfigurationen geschaltet werden können. Die Selbstorganisation der vier Spezies (1-Z, 1-E, 2-Z, 2-E) mit Co II -Ionen wurde nach Änderung der Koordinationsvektoren in Abhängigkeit von der Ligandenkonfiguration (E vs. Z) und dem Regioisomer (1 vs. 2) untersucht. Mit 1-Z bildet sich Co 2 (1-Z) 3 , während mit 2-Z ein undefiniertes Gemisch verschiedener Spezies (Oligomere) beobachtet wurde. Bei Belichtung der E-Konfigurationen mit 385 nm wurde die gegenteilige Situation beobachtet, wobei 1-E Oligomere und 2-E den Komplex Co 2 (2-E) 3 bildete. Der lichtgesteuerte Abbau/Aufbau wurde in einem Ligandenverdrängungsexperiment mit substöchiometrischen Mengen von Co II -Ionen demonstriert. Die abwechselnde Bestrahlung mit violettem und grünem Licht führte zu einer reversiblen Umwandlung zwischen Co 2 (1-Z) 3 und Co 2 (2-E) 3 über mehrere Zyklen hinweg ohne signifikante Ermüdung. Kontrollierter Auf-und Abbau gehören zu den grundlegendsten Prozessen in lebenden Systemen. So führt beispielsweise die durch Licht ausgelöste cis-trans-Isomerisierung von Retinal im Rhodopsin nach mehreren aufeinanderfolgenden Prozessen, über den Zusammenbau von zwei Rhodopsin-Einheiten mit Transducin und den Abbau des heterotrimeren Transducins in zwei seiner drei Komponenten, [1] zur makroskopischen Wahrnehmung von Licht. Reizgesteuerter Auf-und Abbau sind allgegenwärtige Schritte in biologischen Signaltransduktionskaskaden. In natürlichen und synthetischen Systemen ist Licht ein nahezu idealer Stimulus, da es sowohl mit hoher räumlicher und zeitlicher Auflösung als auch in verschiedenen Wellenlängen

Diazocine is a bridged azobenzene with both phenyl rings connected by a CH2-CH2 group. Despite this rather small structural difference, diazocine exhibits improved properties over azobenzene as a photoswitch, such as high switching efficiencies, very high quantum yields, switching wavelengths in the visible range, and most importantly, the fact that it is more stable in the Z configuration, which is particularly expedient in photopharmacology and mechanophore applications. According to our studies presented here, another advantage over conventional azobenzene is now added. In contrast to azobenzenes and other photochromes, diazocine can be switched with two different triplet sensitizers present at the same time in both directions: Z→E as well as E→Z. Experimental and theoretical (CASPT2) studies of triplet excitation energies provide an explanation for this fact. The triplet energies in Z and E azobenzene are almost equal, which prevents selective sensitization of either isomer. In diazocine, the two excitation energies are well-separated, so they can be accessed selectively. Besides offering fundamental physical insight to diazocines, an emerging class of photoswitches, our work opens up a number of potential avenues for utilizing them for example in photopharmacology and smart materials design due to the significant redshift of excitation wavelengths to from blue to green (Z→E) and green to far-red (E→Z), which triplet sensitization offers.