Light, temperature, and pH control of aqueous azopyridine-terminated poly(<i>N</i>-isopropylacrylamide) solutions

Ren, Hao; Qiu, Xing‐Ping; Shi, Yan; Yang, Peng; Winnik, Françoise M.

doi:10.1039/c9py01086f

Cited by 15 publications

(22 citation statements)

References 49 publications

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“…The ability to switch twice over a narrow temperature range from a clear to a turbid to a clear medium, upon heating or cooling, may find applications in sensing, especially since azopyridines exhibit fast dark cis-to-trans isomerization. 40 …”

Section: Discussionmentioning

confidence: 99%

The Two Phase Transitions of Hydrophobically End-Capped Poly(N-isopropylacrylamide)s in Water

et al. 2020

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High-sensitivity differential scanning calorimetry (HS-DSC) thermograms of aqueous poly( N -isopropylacrylamide) (PNIPAM) solutions present a sharp unimodal endotherm that signals the heat-induced dehydration/collapse of the PNIPAM chain. Similarly, α,ω-di- n- octadecyl-PNIPAM (C18-PN-C18) aqueous solutions exhibit a unimodal endotherm. In contrast, aqueous solutions of α,ω-hydrophobically modified PNIPAMs with polycyclic terminal groups, such as pyrenylbutyl (Py-PN-Py), adamantylethyl (Ad-PN-Ad), and azopyridine- (C12-PN-AzPy) moieties, exhibit bimodal thermograms. The origin of the two transitions was probed using microcalorimetry measurements, turbidity tests, variable temperature 1 H NMR (VT-NMR) spectroscopy, and 2-dimensional NOESY experiments with solutions of polymers of molar mass ( M n ) from 5 to 20 kDa and polymer concentrations of 0.1 to 3.0 mg/mL. The analysis outcome led us to conclude that the difference of the thermograms reflects the distinct self-assembly structures of the polymers. C18-PN-C18 assembles in water in the form of flower micelles held together by a core of tightly packed n -C18 chains. In contrast, polymers end-tagged with azopyridine, pyrenylbutyl, or adamantylethyl form a loose core that allows chain ends to escape from the micelles, to reinsert in them, or to dangle in surrounding water. The predominant low temperature ( T 1 ) endotherm, which is insensitive to polymer concentration, corresponds to the dehydration/collapse of PNIPAM chains within the micelles, while the higher temperature ( T 2 ) endotherm is attributed to the dehydration of dangling chains and intermicellar bridges. This study of the two phase transitions of telechelic PNIPAM homopolymer highlights the rich variety of morphologies attainable via responsive hydrophobically modified aqueous polymers and may open the way to a variety of practical applications.

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Section: Discussionmentioning

confidence: 99%

The Two Phase Transitions of Hydrophobically End-Capped Poly(N-isopropylacrylamide)s in Water

et al. 2020

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“…The photoresponsive behavior of the compounds is strongly related to spacers, which can affect the free movement of the molecules . The presence of azopyridine, known for, besides that of H acceptor and ionization ability, its light sensitivity undergoing trans–cis isomerization by UV irradiation, led to the idea of studying the behavior of the coordination compound 1 on irradiation, both in solution and in film. Photo‐responsive polymers, including coordination ones, are of interest in fundamental studies at the interface between photochemistry and polymer science but also for applications in chemistry and biology.…”

Section: Resultsmentioning

confidence: 99%

“…Instead, the relaxation in the dark is achieved after 72 hours. Steric and/or polar effects favorable for cis form to develop intermolecular interactions in the solution, including with the solvent, which would stabilize the conformation somewhat and delay the return to the trans form, in which there are reduced possibilities for the development of intermolecular interactions, could be among the reasons for slow dark relaxation . On the other hand, higher intensity of the absorption band at 284 nm upon return indicates the formation of a higher percentage of trans species as a result of the trans–cis‐trans cycle.…”

Section: Resultsmentioning

confidence: 99%

Nanoscale Coordination Polymer of Dimanganese(II) as Infinite, Flexible Nanosheets with Photo‐Switchable Morphology

Shova¹,

Vlad²,

Damoc³

et al. 2020

Eur J Inorg Chem

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An original co‐ligand association, consisting of 4,4'‐azopyridine and 1,3‐bis(carboxypropyl)tetramethyldisiloxane, is used for complexing MnII, to obtain a 2D dinuclear coordination array having infinite horizontal dimensions and nanometric thickness. Due to the shielding effect of the tetramethyldisiloxane units facing outwards on both sides, the sheets are free of any chemical or physical intermolecular interactions, as crystallographic analysis reveals. The compound shows two glass transitions, at –51 and 33 °C, and begins to decompose at 292 °C. The co‐existence in the structure of the highly hydrophobic tetramethyldisiloxane spacers and the polar metal complexed units confers amphiphilic character to the compound, making it capable of reducing the surface tension of the DMF, from 35.8 to 29.4 mN/m, at a critical micellar concentration around 1 wt.‐% complex. The presence of aggregates in solution is evidenced by dynamic light scattering. The light sensitive azopyridine units make the compound photo‐responsive. This behavior occurs both in solution as well as in the film, where the compound self‐assembles in micellar morphology when UV‐irradiated. Both conductivity and dielectric permittivity of the film increase as a result of trans–cis configuration. Magnetic measurement data indicate two antiferromagnetic coupled spins, S = 5/2, that are able to interact with small external magnetic field, i.e., during MFM scanning.

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“…Aqueous solutions of AzPy-PNIPAM (structure shown in Fig. 2, top) respond to three orthogonal triggers: 47 light, by virtue of the trans-cis isomerization of AzPy, pH via protonation of the pyridine nitrogen of AzPy, and temperature, due to the thermosensitivity of PNIPAM in water. 48 Also, AzPy-PNIPAM self-assembles in water as it bears a dodecyl chain on one end and the AzPy group on the other.…”

Section: Chemical Properties Of Azopyridines and Their Applications In Responsive Polymeric Materialsmentioning

confidence: 99%

“…14 The polymer undergoes a phase transition in water at a temperature (T c , cloud point) that depends on the solution pH. 47 The T c value also changes upon light illumination, since the dipole moments of the trans-AzPy and cis-AzPy are different. An overview of the phenomena observed upon sequential application of the three triggers is given in Fig.…”

Section: Chemical Properties Of Azopyridines and Their Applications In Responsive Polymeric Materialsmentioning

confidence: 99%

Azopyridine: a smart photo- and chemo-responsive substituent for polymers and supramolecular assemblies

2020

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Light, temperature, and pH control of aqueous azopyridine-terminated poly(N-isopropylacrylamide) solutions

Abstract: Azopyridines (AzPy) act as light-sensitive groups that undergo reversible cis–trans isomerization upon UV irradiation, as hydrogen-bond acceptors, and as ionizable moieties.

Cited by 15 publications

References 49 publications

The Two Phase Transitions of Hydrophobically End-Capped Poly(N-isopropylacrylamide)s in Water

The Two Phase Transitions of Hydrophobically End-Capped Poly(N-isopropylacrylamide)s in Water

Nanoscale Coordination Polymer of Dimanganese(II) as Infinite, Flexible Nanosheets with Photo‐Switchable Morphology

Azopyridine: a smart photo- and chemo-responsive substituent for polymers and supramolecular assemblies

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