Cooperative Switching in Nanofibers of Azobenzene Oligomers

Abstract

Next-generation molecular devices and machines demand the integration of molecular switches into hierarchical assemblies to amplify the response of the system from the molecular level to the meso- or macro-scale. Here, we demonstrate that multi-azobenzene oligomers can assemble to form robust supramolecular nanofibers in which they can be switched repeatedly between the E- and Z-configuration. While in isolated oligomers the azobenzene units undergo reversible photoisomerization independently, in the nanofibers they are coupled via intermolecular interactions and switch cooperatively as evidenced by unusual thermal and kinetic behavior. We find that the photoisomerization rate from the Z-isomer to the E-isomer depends on the fraction of Z-azobenzene in the nanofibers, and is increased by more than a factor of 4 in Z-rich fibers when compared to E-rich fibers. This demonstrates the great potential of coupling individual photochromic units for increasing their quantum efficiency in the solid state with potential relevance for actuation and sensing.

Determining the Photoisomerization Quantum Yield of Photoswitchable Molecules in Solution and in the Solid State

“…Azobenzene is one of the oldest photoswitches known, but new derivatives thereof are still being developed27282930. The low energy state of azobenzene is the trans-isomer and the high energy is the cis-isomer, which spontaneously isomerizes back to the trans isomer at ambient temperatures.…”

Light-induced dynamic shaping and self-division of multipodal polyelectrolyte-surfactant microarchitectures via azobenzene photomechanics

“…Energization of the system with continuous, non-polarized blue light produces oscillating populations of trans and cis azoTAB isomers, driving motion at the molecular scale (bending/unbending), which when spatially confined within the mesostructured domains of the microparticles generates a collective response, as recently reported in azobenzene-based supramolecular nanofibers47, eventually leading to mechano-transduction at the micrometre length scale. In this respect, previous studies on photo-isomerization in azobenzene-modified liquid crystal polymers indicate that the corresponding reduction in order parameter on formation of the all- cis state gives rise to anisotropic contractions/expansions in the material27.…”

Reversible Photoisomerization of Monolayers of π‐Expanded Oligothiophene Macrocycles at Solid–Liquid Interfaces

“…[11,12] Diarylethene-and azobenzene-containing molecules are among the most common choices to fabricate photoswitchable self-assembled monolayers. [13][14][15][16][17][18][19] Not only reversibility,but as well the combination of different functionalities such as large structural changes, [20] electronic transport, [21] and host-guest capability, [22] are highly desirable for future generations of versatile photoresponsive molecules and systems.…”