Temperature response of aqueous solutions of pyrene end‐labeled poly(<i>N</i>‐isopropylacrylamide)s probed by steady‐state and time‐resolved fluorescence

Fowler, Michael; Duhamel, Jean; Qiu, Xing Ping; Korchagina, E.V.; Winnik, Françoise M.

doi:10.1002/polb.24543

Cited by 10 publications

(30 citation statements)

References 41 publications

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“…To assess the importance of the chemical composition and the bulk of the end-groups, we recorded the thermograms of two α,ω-telechelic PNIPAMs that do not carry linear n -alkyl moieties. The end groups were either the tricyclic adamantylethyl group (α,ω-diadamantylethyl-PNIPAM, Ad-PN-Ad) 34 or the tetracyclic aromatic 1-pyrenyl-4-butyl group (α,ω-dipyrenylbutyl-PNIPAM, Py-PN-Py) 33 (see structures in Figure 1 ). Their thermograms ( Figure 8 ) are bimodal, with a low temperature endotherm at ( T 1 = 27.5 °C, Δ H 1 = 5.0 kJ/mol) for Ad-PN-Ad and T 1 = 29.5 °C (Δ H 1 = 2.9 kJ/mol) for Py-PN-Py, and a high temperature endotherm centered at T 2 = 32.9 °C, Δ H 2 = 0.9 kJ/mol) in the case of Ad-PN-Ad and T 2 = 31.9 °C, Δ H 2 = 2.1 kJ/mol) in the case of Py-PN-Py.…”

Section: Resultsmentioning

confidence: 99%

“…Water was deionized using a Millipore Milli-Q system. The polymers employed are listed in Table together with their molecular characteristics and a link to the references that describe their preparation by reversible addition–fragmentation transfer (RAFT) radical polymerization of N -isopropylacrylamide (NIPAM). ,, Their structures are presented in Figure .…”

Section: Methodsmentioning

confidence: 99%

“…Since the arms of star micelles are expected to be less constrained The cloud point of HS-PN-AzPy 12K in water is slightly higher than that of C12-PN-AzPy 12K (24.1 vs 23 °C, Figure 6c), revealing a slight increase of the hydrophilicity of the polymer. 10,33 The thermogram of HS-PN-AzPy 12K in neutral water is bimodal (Figure 6d). Both T 1 and T 2 shift to higher temperature, compared to their values in the C12-PN-AzPy 12K solution.…”

Section: Solution Properties Of Hs-pn-azpy 12k In Water: a Comparison...mentioning

confidence: 99%

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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: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Solution Properties Of Hs-pn-azpy 12k In Water: a Comparison...mentioning

confidence: 99%

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

et al. 2020

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“…Information about the mode of excimer formation, either quasi-instantaneous or diffusion controlled, can be gained from the analysis of the rise time of the excimer determined from time-resolved fluorescence decays and from the wavelength of the excimer emission maximum retrieved from the fluorescence spectra. 23,26,28 The photophysical properties of pyrene were exploited recently to monitor PNIPAM samples end-labeled with 1pyrenylbutyl groups acting as hydrophobic substituents. Polymers ranging in molar mass (M n ) from 7.6 to 44.5 kg/mol were prepared and named Py n -PNIPAM, with n equal to 1 or 2, depending on whether one or both ends of the chain were labeled with pyrene.…”

Section: ■ Introductionmentioning

confidence: 99%

“…7,12,28,32 The Py n -PNIPAM samples were found to be faithful reporters of the aggregation below and around T c of lip 2 -PNIPAM chains in water as presented schematically later in the text (see Figure 2). 28 At temperatures below 15 °C, lip 2 -PNIPAMs in water form polymeric flower micelles with a hydrophobic core made of the lipophilic groups stabilized by hydrated PNIPAM loops. The PNIPAM loops of the lip 2 -PNIPAM micelles progressively dehydrate with increasing solution temperature until T c is reached.…”

Section: ■ Introductionmentioning

confidence: 99%

Temperature-Controlled Interactions between Poly(N-isopropylacrylamide) Mesoglobules Probed by Fluorescence

et al. 2018

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The temperature-dependent behavior of aqueous solutions composed of a small amount of monodisperse poly(N-isopropylacrylamide) (PNIPAM) labeled at one or both ends with pyrene (Pyn-PNIPAM with n = 1 or 2) and a 10-fold excess of a non-fluorescent poly(Nisopropylacrylamide) (PNIPAM(22K), Mn = 22,000 g/mol) was characterized using steadystate (SSF) and time-resolved (TRF) fluorescence. Turbidimetry studies indicated that all samples exhibited two temperature-induced transitions: one at Tc, the cloud point of the pyrene-labeled polymers and one at Tc22, the cloud point of PNIPAM(22K). These two transitions were also inferred from a decrease in the excimer-to-monomer fluorescence intensity ratio, namely the IE/IM ratio, obtained from SSF spectra. TRF decays of the pyrene monomer were acquired and fitted with a sum of exponentials to obtain the number average lifetime <>. Plots of <>-versus-temperature also showed transitions at Tc and Tc22. The changes in behavior observed at Tc for both IE/IM and <> were consistent with those observed for solutions of solely Pyn-PNIPAM samples. The transitions found at Tc22 for the Pyn-PNIPAM solutions with PNIPAM(22K) were not observed in aqueous solutions of Pyn-PNIPAM without PNIPAM(22K). They were explained by invoking substantial mixing of labeled and unlabeled chains as temperature exceeded Tc22. This mixing could only occur if the mesoglobules composed of labeled chains were not "frozen" at temperatures above Tc22 despite forming stable entities in this temperature range. This phenomenon was rationalized by considering the difference in the characteristic reptation time of the chains found in a Pyn-PNIPAM and PNIPAM(22K) mesoglobule at temperatures larger than Tc22.

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Synthesis, Photophysical and Electronic Properties of New Red‐to‐NIR Emitting Donor–Acceptor Pyrene Derivatives

Merz

Dietz

Vonhausen

et al. 2019

Chemistry A European J

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We synthesized new pyrene derivatives with strong bis(para‐methoxyphenyl)amine donors at the 2,7‐positions and n‐azaacene acceptors at the K‐region of pyrene. The compounds possess a strong intramolecular charge transfer, leading to unusual properties such as emission in the red to NIR region (700 nm), which has not been reported before for monomeric pyrenes. Detailed photophysical studies reveal very long intrinsic lifetimes of >100 ns for the new compounds, which is typical for 2,7‐substituted pyrenes but not for K‐region substituted pyrenes. The incorporation of strong donors and acceptors leads to very low reduction and oxidation potentials, and spectroelectrochemical studies show that the compounds are on the borderline between localized Robin‐Day class‐II and delocalized Robin‐Day class‐III species.

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Temperature response of aqueous solutions of pyrene end‐labeled poly(N‐isopropylacrylamide)s probed by steady‐state and time‐resolved fluorescence

Cited by 10 publications

References 41 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

Temperature-Controlled Interactions between Poly(N-isopropylacrylamide) Mesoglobules Probed by Fluorescence

Synthesis, Photophysical and Electronic Properties of New Red‐to‐NIR Emitting Donor–Acceptor Pyrene Derivatives

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