Azobenzene-Equipped Covalent Organic Framework: Light-Operated Reservoir

Abstract

Light-operated materials have gained significant attention for their potential technological importance. To achieve molecular motion within extended networks, stimuliresponsive units require free space. The majority of the so far reported 2D-extended organic networks with responsive moieties restrict their freedom of motion on account of their connectivity providing constrained free volume for efficient molecular motion. We report here a light-responsive azobenzene-functionalized covalent organic framework (TTA-AzoDFP) designed in a way that the pendent azobenzene groups are pointing toward the pore channels with sufficient free volume necessary for the unencumbered dynamic motion to occur inside the pores of the covalent organic framework (COF) and undergo a reversible trans−cis photoisomerization upon light irradiation. The resulting hydrophobic COF was used for the storage of rhodamine B and its controlled release in solution by the mechanical motion of the azobenzene units triggered by ultraviolet-light irradiation. The TTA-AzoDFP displayed unprecedented photoregulated fluorescence emission behavior upon UV-light irradiation. Size, emission, and degree of hydrophobicity with respect to trans−cis−trans photoisomerization could be reversibly controlled by alternating UV-and visible-light exposure. The results reported here demonstrate once again the importance of the careful design of the linkers not only to allow the incorporation of molecular switches within the chemical structure of COFs but also to provide the required free space for not hindering their motion. The results demonstrate that responsive COFs could be suitable platforms for delivery systems that can be controlled by external stimuli.

Redox-triggered switching in three-dimensional covalent organic frameworks

“…For example, Jiang et al reported an anthracene-based 2D COF, which can show structural transformations by alternating UV light irradiation and heating 38 . Trabolsi et al reported an azobenzene-equipped 2D COF that can be used as light-operated reservoir 41 . Unfortunately, although these systems have shown interesting stimuli-responsive properties, there still has some problems that need to be further improved, such as inefficient conversion.…”

Light: A Magical Tool for Controlled Drug Delivery

“…The synthesized covalent organic framework could be effectively utilized for rhodamine B storage and on‐demand release ( Figure A). [ 205 ]…”

“…Reproduced with permission. [ 205 ] Copyright 2019, American Chemical Society. B) Chemical structures of phototrexate in the trans and cis configurations.…”

Tunable electrical properties of carbon dot doped photo-responsive azobenzene–clay nanocomposites

“…Also, they differ in their planarity with the trans form assuming a planar form with C 2h symmetry and the cis form assuming a nonplanar form with C 2 symmetry. 12 As such, the photoresponsive azobenzene has been used in incorporation with polymeric materials, 13,14 different nanostructured materials 15,16 and metal-organic frameworks [17][18][19] for energy storage applications.…”