Light‐Orchestrated Macromolecular “Accordions”: Reversible Photoinduced Shrinking of Rigid‐Rod Polymers

Abstract

Light can play: Irradiation causes dramatic changes in the shape of rigid-rod polymers incorporating azobenzene photochromes in the main chain. The embedded photoswitches act as hinges, which upon light-induced isomerization lead to reversible shrinking and stretching of the polymer backbone (see scheme), resembling light-orchestrated macromolecular accordions.

Multi‐stimuli‐responsive Polymers Based on Calix[4]arenes and Dibenzo‐18‐crown‐6‐ethers

“…Amphiphilic azopolymers 55 have been used in self-assembly processes to produce thin films, micelles, vesicles and manufacture surface relief gratings. An interesting example of translation of the change in structure upon trans to cis photoisomerization towards change of size in a main chain azopolymer has been demonstrated by Bléger et al 56 The azobenzene-containing poly(paraphenylene)s, (PPPs) had been decoupled by means of distorted twisted angles on the phenylene unit as a result of its substitution with long aliphatic chains, thus enabling a cis-rich state of the chromophores upon irradiation in this rigid system. This strategy is promising towards preparation of new photoactuators.…”

Fluorescent Dyes Used in Polymer Carriers as Imaging Agents in Anticancer Therapy

“…Light is a useful trigger to manipulate ion channels externally, because does not change the chemical environment of the studied system. The synthetic molecules called "molecular photoswitches" e.g., photocaged small molecules like coumarin derivatives [198] or azobenzenes [199], spiropyranes [200], and malachite green leuconitriles [196] can change their structure and properties upon light irradiation. These dyes are often characterized by having two or more isomeric forms.…”

“…Furthermore, UV-irradiation of azobenzene molecules promotes the trans-cis isomerization at the central double bond, resulting in considerable changes in geometry and polarity [203,204]. Azobenzene is known to exist in cis (loose spacing) and trans (tight spacing) configurations in dark and light conditions, respectively [205,206]. This reversible process is controlled both thermally and by irradiation with visible light [207].…”

Successive Translocation of the Rings in a [3]Rotaxane

“…[9][10][11] Others are better viewed as information processors, [12] or function as single-molecular chemical factories. [13,14] For the design of molecular muscles different approaches have been explored, [15][16][17][18] but the use of mechanically interlocked building blocks is advantageous because it allows to put constraints on the relative movements of the components. [19][20][21][22][23][24][25][26][27] In the present work, we describe the translation of either one or both of the macrocyclic rings in a [3]rotaxane by one-electron or two-electron reduction of a central diimide.…”