The pseudobinary phase diagram cis-/trans-azobenzene and the cis → trans isomerization in various states of aggregation

Abstract

Azobenzene, Phase Diagram cis-/trans-azobenzene, Kinetics of IsomerizationThe pseudobinary phase diagram of trans-azobenzene and the thermally instable cis-isomer was examined by thermomicroscopical and DSC-measuremsnts. Two eu~ectic temperatures have been determined (at 41.4 C and 36.7 C). The latter occurs only in the presence of a metastable polymorph of cis-azobenzene after quenching a melt, that contained as well cis-as trans-azobenzene, presumable under conditions of heterogeneous nucleation. In the melt and in solution the thermally induced cis-trans-isomerization follows first order kinetics. Below the eutectic temperature the rate is controlled by three-dimensional nuclei growth to reaction extent 0.20. Between the eutectic temperature and the melting points of product respectively educt the kinetics follow the PROUT-TOMPKINS law. The reason is the increasing isomerization rate with increasing fraction of melt.

Photoinduced Reversible Solid‐to‐Liquid Transitions for Photoswitchable Materials

“…More precise measurements of T m of trans and cis azobenzenes and their mixtures with different trans/cis ratios were conducted by two groups (Figure 4). [30] clearly show that T m of the mixtures of trans and cis azobenzenes with ac ertain ratio can be much lower than those of pure trans or cis azobenzene.T herefore,a sl ong as the eutectic temperature is lower than room temperature,itis possible to achieve photoinduced solid-to-liquid transition even if both T m of trans and cis isomers of an azobenzene derivative are above room temperature.…”

“…Eligehausen et al. determined that the mixtures of trans and cis azobenzenes had two eutectic temperatures at 41.4 °C and 36.7 °C, respectively . Although the eutectic temperature determined by Hartley, Galashin and Yakovlev, and Eligehausen et al.…”

Photoinduzierte, reversible Fest‐flüssig‐Übergänge unter Verwendung photoschaltbarer Materialien

“…stellten fest, dass die Mischungen von trans ‐ und cis ‐Azobenzolen zwei eutektische Temperaturen bei 41.4 bzw. 36.7 °C zeigten . Obwohl die von Hartley, Galashin und Yakovlev sowie Eligehausen et al.…”

“…Der Einfluss des cis ‐Gehalts von Azopolymeren auf die T g unterscheidet sich von dem des cis ‐Gehalts von niedermolekularen Azobenzolverbindungen auf den T m . Mischungen von trans ‐ und cis ‐Azobenzolen hatten eine eutektische Temperatur, die niedriger war als der T m sowohl von trans ‐ als auch von cis ‐Isomeren (Abbildung ) . Allerdings nahm die T g des Azopolymers 32 mit zunehmendem cis ‐Gehalt ab …”

Photoactive and Physical Properties of an Azobenzene-Containing Coordination Framework

“…The physical change is accompanied by an induced dipole moment change from 0 to 3 Da, respectively, [27] and a change in melting point of azobenzene. [28] An important property of these molecules is the reversibility of the light-induced changes, enabling the material to be used over multiple cycles. [29][30][31] The reverse reactions (from the cis to the trans form) require visible light irradiation or heating the sample.…”