Control of the Orientation and Photoinduced Phase Transitions of Macrocyclic Azobenzene

Abstract

Photoinduced phase transitions caused by photochromic reactions bring about a change in the state of matter at constant temperature. Herein, we report the photoinduced phase transitions of crystals of a photoresponsive macrocyclic compound bearing two azobenzene groups (1) at room temperature on irradiation with UV (365 nm) and visible (436 nm) light. The trans/trans isomer undergoes photoinduced phase transitions (crystal–isotropic phase–crystal) on UV light irradiation. The photochemically generated crystal exhibited reversible phase transitions between the crystal and the mesophase on UV and visible light irradiation. The molecular order of the randomly oriented crystals could be increased by irradiating with linearly polarized visible light, and the value of the order parameter was determined to be −0.84. Heating enhances the thermal cis‐to‐trans isomerization and subsequent cooling returned crystals of the trans/trans isomer.

Organic Photofunctional Materials Composed of Azobenzene Derivatives: Liquid-solid Phase Transition in Multi Azobenzene Compounds with Partially Substituted Structures

“…[7,8,9,] Amongst them, we have recently reported light responsive, reworkable adhesives in multi azobenzene compounds with reversible liquid-solid phase change properties. [10] Related phase transitions have been reported for fluidization of azobenzene polymers using irradiation with light [11], changing the melting point in crystals of diarylethanes using photoisomerization [12,13] and "photomelting" of crystals of cyclic azobenzene dimers at room temperature [14,15]. Multi-azobenzene compounds that we demonstrated the first, reversible adhesion force change upon light stimulation are tetra-, hexa-, or octa-substituted sugar alcohols bearing mesogenic azobenzene chains.…”

Photoinduced reversible switching of porosity in molecular crystals based on star-shaped azobenzene tetramers

“…3d, Supplementary Figs 18, 34 and 38). A detailed examination of the effect of light on the E 4 -1c crystals reveals an even more interesting behaviour, not observed for previously investigated azobenzene-containing crystals 21,23,24 : exposure to UV light for a short time causes no significant change in morphology but affords a dramatic decrease in the birefringence, which is fully restored by heating (Supplementary Fig. 38).…”

“…3c), thus enabling photons to reach the core of the crystals. To the best of our knowledge, substantial E → Z photoisomerization of azobenzenecontaining crystals has only been described in two recent reports on azobenzene cyclophanes bearing long alkyl substituents 23,24 .…”

Photon energy storage materials with high energy densities based on diacetylene–azobenzene derivatives

“…Even without the templates, we expect that the intermolecular interactions such as H-bonding, van der Waals force, and p-p interaction can signicantly inuence the photon energy storage density. The photoswitching vs. packing density and alignment of azobenzene materials has been explored for some macrocyclic [21][22][23] and linear 24 azobenzene derivatives, particularly for liquid crystalline materials, for applications in photolithography and actuation. The collective change of the intermolecular interactions in such materials can be observed as a macroscopic solid-liquid phase transition.…”