Are Two Azo Groups Better than One? Investigating the Photoresponse of Polymer-Bisazobenzene Complexes

Abstract

Azobenzene chromophores are an ideal choice for material applications where functionality needs to be activated in a precise remote-controlled fashion. The azobenzene stimuli-response falls into two categories, either based on efficient trans-to-cis photoisomerization and a high cis yield enabling on−off type functions, or relying on a fast trans−cis−trans cycling creating motion in the material system. Herein, we show that using bisazochromophores instead of the more common monoazobenzene derivatives makes a difference in the performance of light-responsive azopolymers, more specifically in photo-orientation and all-optical surface patterning. Our findings point out that polymer-bisazobenzene complexes are an attractive alternative as high-performance photoreponsive materials and that although their properties are highly sensitive to the extent of conjugation in the system, they can be designed into relatively transparent films with high performance for all-optical patterning.

Volume generation towards dynamic surface morphing in liquid crystal polymer networks

“…This is stimulated even more by dual wavelength exposure promoting both excitation of trans and the cis isomer of azobenzene rather than populating cis isomer solely. This dynamics was proposed to be responsible for the lateral transport of azobenzene-modified side-chain polymers under the exposure with an interference pattern of a laser source [49]. Here, we anticipate its importance in our densely cross-linked networks where the dynamics in the azobenzene isomerisation enhances the formation of molecular voids in the polymer matrix resulting in a large volume increase on the macroscopic level.…”

Light‐Driven Soft Robot Mimics Caterpillar Locomotion in Natural Scale

“…The actuation is associated with the light-induced heat generation rather than via trans-cis isomerization since: (i) The excitation wavelength (532 nm) matches neither the trans-cis absorption of azo molecules in the ultraviolet, nor the wavelength for bidirectional isomerization (trans-cis and cis-trans at the same time) in azo molecules around 490 nm [20] ; (ii) The azo molecular concentration (1 wt%) is too low to trigger fast mechanical actuation by photochemical effects; (iii) Strong laser excitation intensity (tens of Watts per cm 2 ) and dye bleaching suggest light-induced heat effects in the system. There are several parameters that govern the stepping dynamics.…”

Supramolecular design principles for efficient photoresponsive polymer–azobenzene complexes

“…This allowed assessing the effect of chromophore polarity, bulkiness, and length on photo-orientation. 91,94,[112][113][114][115] Focusing first on molecules 1-4 (1 = NHA above), which differ only in their substitution at the tail (nonbonding) end of the azobenzene, it was shown that this change was enough to make a drastic difference in the photoresponsive behavior of the complexes. Fig.…”

“…Even though isotropic, photo-orientation was observed in all of these materials, and when comparing P4VP(5) to P4VP (8), it was shown that the larger aspect ratio of 5 gave rise to a 4-fold increase in birefringence when using the same azobenzene concentration. 115 Also, two conclusions of practical importance for the selection of inscription wavelength were drawn. First, the electronic structure of 6 greatly broadened the absorption spectrum, making it possible to inscribe birefringence over a wide range of wavelengths, from 375 nm to 633 nm.…”

“…112 Second, the writing wavelength comparison for P4VP(7) and P4VP (8) showed that, in order to reach significant birefringence levels, it is important to use the wavelength that drives the photoisomerization reaction in both isomerization directions (trans-to-cis and cis-to-trans), even when that wavelength (488 nm) lies far from the absorption maximum (356 nm for P4VP(7) and 354 nm for P4VP (8)). 115 In general, the ability to record birefringence at wavelengths barely absorbed by the material may be beneficial for applications such as optical holography, 118,119 where low penetration depth of conventional azobenzene-containing polymers may become a limiting factor. One pertinent question provoked by these studies is the role of the strength of the hydrogen-bonding interaction.…”