Synthesis and Isomerization Studies of Cyclotrisazobiphenyl

Abstract

We report an efficient synthesis of cyclotris[(E)-3'-(biphenyl-3-yldiazenyl)] compounds (CTBs). An unsubstituted CTB molecule is accessible in four steps in 10% yield overall, whereas a hexa(methoxymethyl ether) CTB analogue was prepared in nine steps (26% yield). The final macrocyclization step was accomplished in up to 80% yield by using a metal-template effect. Furthermore, the photochromic properties were investigated, and all four isomers were detected and characterized by NMR spectroscopy. A strong influence from the solvent and the irradiation wavelength on the switching process was observed. Irradiation in pyridine yielded the highest amount of the all-Z isomer in the photostationary state. For a full conversion to the all-E isomer, the reaction has to be heated to 45 °C. The isomerization to the all-E isomer is slow at room temperature, with a half-life time of the all-Z isomer of more than nine days in dimethyl sulfoxide (DMSO). Conditions were established to access each possible isomer as the major component in the photostationary state.

Anziehung oder Abstoßung? London‐Dispersionswechselwirkungen kontrollieren Azobenzol‐basierte molekulare Schalter

“…Es konnte auch gezeigt werden, dass die Einbindung der Azoeinheit in makrocyclische Systeme die Isomerisierungseigenschaften beeinflusst. [17] Des Weiteren wurden Arbeiten über die Integration in Foldamere [18] und Polymere [19] publiziert. Im Fall der Schaltung in fester Phase sind schwache intermolekulare Effekte wie Va n-der-Waals-Kräfte entscheidend.…”

“…Die Azobenzoleinheit nimmt dabei eine herausragende Rolle ein, da sie mittels Licht zwischen E-u nd Z-Isomer geschaltet werden kann. [17] Des Weiteren wurden Arbeiten über die Integration in Foldamere [18] und Polymere [19] publiziert. [15] Das zunehmende Interesse hat zu einem starken Anstieg von Publikationen geführt, in welchen die Effekte von verschiedenen Substituenten auf die Isomerisierung vom thermodynamisch instabilen Z-z um stabilen E-Isomer untersucht wurden.…”

Synthesis of 4-substituted azopyridine-functionalized Ni(II)-porphyrins as molecular spin switches

“…The nitroso compounds 3 and 6 were synthesized by two different methods. 1-Bromo-3-nitrosobenzene ( 3 ) was obtained by oxidation of 3-bromoaniline ( 2 ) using Oxone ™ (Wegner et al [ 19 – 21 ], Scheme 1 ). Isolation of 3 was achieved, however, a one pot approach including a subsequent Baeyer–Mills reaction to yield 10 is preferred.…”

meta-Oligoazobiphenyls – synthesis via site-selective Mills reaction and photochemical properties

“…In this respect, we planed a combination of the Mills reaction [27] with Suzuki cross-coupling, which we have successfully employed in previous studies (Fig. 2) [28]. A key issue, however, was a site-selective transformation in order to differentiate both ends of the oligomer.…”