Orchestrating Molecular Motion with Light – From Single (macro)Molecules to Materials

Abstract

The possibility to control molecular systems with light holds much promise for the fi elds of materials and life sciences. To achieve such control, compounds that are able to reversibly photo isomerize between two states or more can be employed. Several classes of photochromic units are available depending on which properties should be modulated upon isomerization, e.g., electronic gap, polarity, or geometry. The latter class, which is mostly based on E/Z isomerization, is particularly useful to remotely trigger motion at the single molecule level, giving rise to a wide range of applications at all scales after incorporation into the adequate architecture. In this article, recent advances in that direction are highlighted, including our own efforts to optimize the intrinsic properties of azobenzene photoswitches, as well as their integration into oligomers, polymers, and 3D frameworks.

Photoswitchable double bonds: Synthetic strategies for tunability and versatility

“…Interest in the study and use of bi‐stable molecular switches has risen in the last decade, due in part to the ability to fine‐tune these molecular tools. A number of excellent review articles have recently been published on biomolecules, polymers, data storage devices, and other dynamic molecular systems containing photoswitches . This mini‐review will focus on one of the most common functional group transformations that are exploited in molecular switches—isomerization about double bonds—and will specifically highlight recent discoveries in how to control photochemical and physical properties, as well as how to access unusual switching motifs.…”

Modeling of Stripe Patterns in Photosensitive Azopolymers

“…While it proved difficult to apply the volume forces in the ANSYS software, which operates only with the forces applied to the nodes (and thus the total force changes with the remeshing), we chose an alternative way of applying the light induced stress. For that we proved, using a home-made finite element software, that the stretching volume force (13) applied to the elastic solid at previously mentioned boundary conditions induces the same deformation field as the traction force acting normally on the upper sample surface in negative direction (inwardly): t z (x) = −τ max exp(− 2(x−a) 2 w 2 ) with τ max = τ 0 . Similarly, the contractive volume force (14) is equivalent to the traction force acting in positive direction (outwardly): t z (x) = τ max exp(− 2(x−a) 2 w 2 ) with τ max = τ 0 /2.…”

“…For that we proved, using a home-made finite element software, that the stretching volume force (13) applied to the elastic solid at previously mentioned boundary conditions induces the same deformation field as the traction force acting normally on the upper sample surface in negative direction (inwardly): t z (x) = −τ max exp(− 2(x−a) 2 w 2 ) with τ max = τ 0 . Similarly, the contractive volume force (14) is equivalent to the traction force acting in positive direction (outwardly): t z (x) = τ max exp(− 2(x−a) 2 w 2 ) with τ max = τ 0 /2. In both cases, to test the strength of effect, we applied different maximal tractions τ max at the stripe center, ranging from 40 MPa to 80 MPa.…”

“…Azobenzene-containing materials are known as highly versatile systems which have many applications in different fields. These materials can be used as molecular switches [1][2][3] and fancy molecular motors [4], because the parent azobenzene exists in two isomeric forms, which can be interchanged using light of appropriate wavelength or heat [5]. The light responsive materials made of azopolymers are used in liquid crystalline technology [6][7][8][9] and as smart polymers for soft-robotics [10][11][12].…”

Dual Stimuli-Responsive P(NIPAAm-co-SPA) Copolymers: Synthesis and Response in Solution and in Films

“…There are a broad range of examples of photo-responsive low-molecular-weight molecules. Fihey [24] and Bleger [25] identified the most prominent photo-responsive molecules: azobenzenes [26,27], diarylethenes [28,29,30,31], and spiropyrans. Numerous derivatives of these molecules have been synthesized to tune the excitation wavelength, response kinetics, and photostability, and to allow these functional moieties to be incorporated into polymeric materials.…”