Photomechanical Energy Transfer to Photopassive Polymers through Hydrogen and Halogen Bonds

Vapaavuori, Jaana; Heikkinen, Ismo T. S.; Dichiarante, Valentina; Resnati, Giuseppe; Metrangolo, Pierangelo; Sabat, Ribal Georges; Bazuin, C. Géraldine; Priimägi, Arri; Pellerin, Christian

doi:10.1021/acs.macromol.5b01813

Cited by 27 publications

(52 citation statements)

References 48 publications

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“…25 The benefits of halogen bonding, such as the high directionality and tunability, 26−28 have recently been recognized in the design of functional materials. 29,30 In particular, halogen-bonded, azobenzene-containing co-crystals 31−33 and (amorphous) supramolecular side-chain polymers 34,35 have shown extremely interesting photoresponsive properties, even superior to their hydrogen-bonded counterparts. Since the first demonstration in 2004, 36 several halogen-bonded LCs have been reported.…”

Section: Introductionmentioning

confidence: 99%

Efficient Light-Induced Phase Transitions in Halogen-Bonded Liquid Crystals

et al. 2016

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Here, we present a new family of light-responsive, fluorinated supramolecular liquid crystals (LCs) showing efficient and reversible light-induced LC-to-isotropic phase transitions. Our materials design is based on fluorinated azobenzenes, where the fluorination serves to strengthen the noncovalent interaction with bond-accepting stilbazole molecules, and increase the lifetime of the cis-form of the azobenzene units. The halogen-bonded LCs were characterized by means of X-ray diffraction, hot-stage polarized optical microscopy, and differential scanning calorimetry. Simultaneous analysis of light-induced changes in birefringence, absorption, and optical scattering allowed us to estimate that <4% of the mesogenic units in the cis-form suffices to trigger the full LC-to-isotropic phase transition. We also report a light-induced and reversible crystal-to-isotropic phase transition, which has not been previously observed in supramolecular complexes. In addition to fundamental understanding of light-responsive supramolecular complexes, we foresee this study to be important in the development of bistable photonic devices and supramolecular actuators.

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Section: Introductionmentioning

confidence: 99%

Efficient Light-Induced Phase Transitions in Halogen-Bonded Liquid Crystals

et al. 2016

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“…For example, our studies indicate that phenolic hydrogen bond and iodoacetylenebased halogen bond with poly(4-vinylpyridine) (P4VP) are relatively stable upon trans-cis-trans cycling. 84 Such studies, assessing the photostabilities of different supramolecular bonds, should be extended, for instance, to different temperatures. Yet already the first experiments 85 highlight that supramolecular bonds are effective for kinetic energy transfer between the phototoactive azobenzene units and the photopassive polymer.…”

Section: Characterization Of the Supramolecular Bondmentioning

confidence: 99%

“…This was attributed to the much higher orientation of the halogenfunctionalized azo unit, which in turn was related to the higher T g of the halogen-bonded complex. 84 The advantage of the more directional nature of halogen bonding has also been pointed out in nonlinear optics. A simple mutation of the halogen from iodine to bromine in halogen-bonded azobenzene-P4VP complexes more than doubled second-harmonic generation upon all-optical poling of the materials.…”

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confidence: 94%

“…125,126 To further compare halogen bonding with hydrogen bonding, we employed PM-IRSAS to show that the passive pyridine moiety in P4VP can rotate in concert with the photo-orienting azobenzene. 84 Even though the interaction strength of halogen bonding is less than that of hydrogen bonding, it gave rise to more pronounced pyridine orientation upon illumination. This was attributed to the much higher orientation of the halogenfunctionalized azo unit, which in turn was related to the higher T g of the halogen-bonded complex.…”

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Supramolecular design principles for efficient photoresponsive polymer–azobenzene complexes

2018

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a Noncovalent binding of azobenzenes to polymers allows harnessing light-induced molecular-level motions (photoisomerization) for inducing macroscopic effects, including photocontrol over molecular alignment and self-assembly of block copolymer nanostructures, and photoinduced surface patterning of polymeric thin films. In the last 10 years, a growing body of literature has proven the utility of supramolecular materials design for establishing structure-property-function guidelines for photoresponsive azobenzene-based polymeric materials. In general, the bond type and strength, engineered by the choice of the polymer and the azobenzene, influence the photophysical properties and the optical response of the material system. Herein, we review this progress, and critically assess the advantages and disadvantages of the three most commonly used supramolecular design strategies:hydrogen, halogen and ionic bonding. The ease and versatility of the design of these photoresponsive materials makes a compelling case for a paradigm shift from covalently-functionalized side-chain polymers to supramolecular polymer-azobenzene complexes.

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“…Supramolecular material design, which employs spontaneously forming noncovalent bonds, such as hydrogen and halogen bonding, between photoactive azobenzenes and photopassive polymers, provides a window of opportunity to delve more deeply into the question of main chain versus side group orientation, since it is easy to prepare supramolecular assemblies with variable spacer lengths, including spacer‐free structures. By applying polarization modulation infrared structural absorbance spectroscopy (PM‐IRSAS)—a method derived from PM‐IRLD that, in addition, is capable of recording the absolute parallel and perpendicular absorbance spectra simultaneously, and thus can determine the structural absorbance spectrum and quantify the photo‐orientation in situ—we demonstrated that the larger photo‐orientation of iodoacetylene‐capped halogen‐bonded azobenzenes compared to their hydrogen‐bonded and nonbonded analogues leads to larger photo‐orientation of the passive pyridine moiety of the poly(4‐vinylpyridine) host but to no orientation of the main chain . IR spectroscopy further allows distinguishing the occupied and free pyridine moieties in these supramolecularly bonded complexes.…”

Section: Photo‐orientation Of Azobenzenes and Photocontrol Of Passivementioning

confidence: 99%

Taming Macromolecules with Light: Lessons Learned from Vibrational Spectroscopy

Vapaavuori

Bazuin

Pellerin

2017

Macromol. Rapid Commun.

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application of vibrational spectroscopy to rotaxane-based molecular machines, [11] molecular motors, [12] and molecule-based electronics, such as molecular electronic switches, [13] are highly recommended.In this feature article, we will focus on one of the most commonly used photoswitches, both for materials engineering and biological applications, namely, azobenzene. [14] This motif is known to change its geometry upon illumination with ultraviolet or visible light, in a socalled photoisomerization reaction from the thermodynamically stable trans conformation to the bent cis conformation (Figure 1a). [15,16] This reaction can be used to both decrease and destroy existing order in materials, as in the cases of photoinduced unfolding of azobenzenecrosslinked alpha-helical peptides, [17] photo induced nematic-isotropic phase transitions [18] and isothermal solid-toliquid transitions, [19] or, on the contrary, to induce order and anisotropy in initially isotropic or less ordered materials, such as in photoinduced birefringence, photoinduced chirality, alloptical poling, and surface relief grating (SRG) formation. [2,20,21] The photoisomerization of individual azobenzene moieties is known to occur in the picosecond timescale and results in changes in its molecular dimensions and properties, such as its dipole moment, solubility and UV-vis absorption. [15] Apolar azobenzene molecules typically have well isolated cis and trans absorption bands along with long thermal cis lifetimes. They are therefore suitable for optical switching applications where two "stable" long-lived states are required. By contrast, functionalizing azobenzene molecules with electron donating and electron withdrawing substituents (or push-pull substitution) alters their photochemistry, typically leading to an overlap of cis and trans absorption bands and thus to quasi-continuous photoswitching between the trans and the cis geometrical isomers. [15,16] Examples of drastic changes in material systems resulting from bistable photoswitching between trans and long-lived cis isomers are illustrated in Figure 1b-d and include photoswitching of the tilt of liquid crystals by an azopolymer command layer, [22] the light-powered contraction of a helical ribbon of a liquid crystalline azopolymer, mimicking plant tendrils, [23] and the photoinduced decrease in helix content of a peptide cross-linked by an azobenzene. [17] Demonstrations of the use of continuous azobenzene photoswitching between the two geometrical isomers, shown in Figure 1e

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Photomechanical Energy Transfer to Photopassive Polymers through Hydrogen and Halogen Bonds

Cited by 27 publications

References 48 publications

Efficient Light-Induced Phase Transitions in Halogen-Bonded Liquid Crystals

Efficient Light-Induced Phase Transitions in Halogen-Bonded Liquid Crystals

Supramolecular design principles for efficient photoresponsive polymer–azobenzene complexes

Taming Macromolecules with Light: Lessons Learned from Vibrational Spectroscopy

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