Photoinduced Bending of Single Crystals of a Linear Bis‐Olefin via Water‐Templated Solid‐State [2+2] Photopolymerization Reaction

Abstract

The single crystals of two structural isomers of bis‐olefinic molecules were shown to have contrasting properties in terms of their photoreactivity: one exhibits an excellent ability to form polymers, accompanied with bending of crystals upon irradiation, while the other is photostable. The photoreactive crystal is a first example in which [2+2] polymerization leads to bending of the crystals, with implications for the design of photoactuators. The hydrate formation ability of one of these molecular isomers promotes the solid‐state reactivity in its crystal, as the H2O molecules act as a template to bring the olefin molecules into the required arrangement for [2+2] polymerization. Further, the crystals of the polymer exhibited better flexibility and smoothed surfaces compared to those of the monomers. In addition, under UV‐light the diene emits bluish violet light while the polymer emits green light, indicating that the luminescence property can be tuned through photoirradiation.

Solvent-Free and Catalyst-Free Synthesis of Cross-Linkable Polyfumaramides via Topochemical Azide-Alkyne Cycloaddition Polymerization

“…Gratifyingly, the intensities of olefinic proton signals of P1 diminished, and two new cyclobutane proton signals appeared at 4.03 and 4.06 ppm as revealed by the 1 H NMR analysis (Figure d). The chemical shifts of these new signals (4.06 and 4.03 ppm) match with those of the cyclobutane protons reported in the literature. , This confirms the formation of the cross-linked polymer via the [2+2] cycloaddition reaction. It is to be noted that all the trans-olefinic units did not undergo [2+2] cycloaddition, but some of them underwent trans–cis isomerization (a cis-olefinic signal at 6.23–6.11 ppm), and some of them remained intact (trans-olefinic signal at 6.82–6.79 ppm).…”

Single-Crystal-to-Single-Crystal [2 + 2] Photocycloaddition Reaction in a Photosalient One-Dimensional Coordination Polymer of Pb(II)

“…Stimuli-responsive materials toward the advancement of molecular actuators that function in response to external stimuli such as light, heat, electricity, , magnetism, and mechanical force , are at the forefront of investigations in recent times. Various mechanical changes including curling, bending, twisting, elongation or contraction, and/or locomotion such as jumping, flipping, and rotations are generally induced in these materials. − A lot of attention has been devoted to the development of these types of materials with a wide range of potential applications in electrochemistry, smart medical devices, artificial muscles, sensors, flexible electronics and probes, etc. − Moreover, mechanical actuators that can work in precision in a noncontact and noninvasive manner are particularly more attractive for remotely controllable actuation. − In this context, photoactuation has garnered considerable attention where the actuation property can be triggered because of photomechanical and photothermal phenomena. − Evolution of dynamic molecular crystals showing photoinduced mechanical motions such as bending, twisting, jumping, and breaking has been studied in the isomerization of azobenzenes, − [4 + 4] dimerization of anthracenes, − cyclization and cycloreversion of diarylethenes, − and [2 + 2] photocycloadditions − by translating nanoscopic structural perturbation at the molecular level to macroscopic crystals in an impressive manner.…”

Mechanical Bending and Modulation of Photoactuation Properties in a One-Dimensional Pb(II) Coordination Polymer

“…1,[5][6][7] A new class of macroscopic crystals also known as "soft crystals" exhibit mechanical movements induced by pressure, heat, and light which often results in hopping, splitting, bending, curling, coiling, twisting, swimming of the crystals. 1,[8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] With the upsurge of dynamic crystals, several examples of mechanically flexible crystals have been reported in the literature showing elastic and plastic deformation upon the application of an external force. [27][28][29][30][31][32][33][34] Apart from actuation by mechanical force, photomechanical actuation is of great advantage due to its remotely controlled process.…”