EPR‐Spektroskopische Charakterisierung lokaler nanoskopischer Heterogenitäten beim thermischen Kollaps thermoresponsiver dendronisierter Polymere

Junk, Matthias J. N.; Li, W.; Schlüter, A. Dieter; Wegner, Gerhard; Spieß, Hans Wolfgang; Zhang, A.; Hinderberger, Dariush

doi:10.1002/ange.201001469

Cited by 15 publications

(25 citation statements)

References 54 publications

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“…While g iso of species B varied from 2.0061 to 2.0058, all other spectroscopic values resembled those of the static inhomogeneities. We have also recently observed such inhomogeneities that are dynamic in nature in a series of dendronized thermoresponsive polymers 5a. 8 Interestingly, in the wide realm of Pluronics triblock copolymers we find both, static and dynamic inhomogeneities.…”

Section: Resultssupporting

confidence: 53%

“…In contrast, the shifting hyperfine coupling values of both species A and B for F68, F108, and F127 with PEO≥70 % could be explained by spin probes B exchanging between hydrophilic and hydrophobic environments on EPR timescales 5a. If a spin probe of species B exchanges fast enough (>10 7 s −1 ) between two environments, one only detects one line at an averaged field position between the pure species A and B.…”

Section: Resultsmentioning

confidence: 92%

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Synthesis, Characterization, and Spectroscopic Analysis of Antiaromatic Benzofused Metalloporphyrins

Sugawara

Hirata

Kojima

et al. 2012

Chemistry A European J

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A two-electron oxidation of the Cu(II) (9) and Zn(II) (12) complexes of tetraphenyltetrabenzoporphyrin (TPTBP) results in the formation of stable antiaromatic [(TPTBP)Cu(II)(H(2)O)](2+)⋅2 [SbF(6)](-) (10) and [(TPTBP)Zn(II)(H(2)O)(2)](2+)⋅2 [SbF(6)](-) (13) with 16π electrons on the inner ligand perimeter. X-ray structures of the parent TPTBP complexes, the dications, and singly oxidized species [(TPTBP)Cu(II)](⋅+)[SbF(6)](-) (11) reveal that the use of TPTBP rather than a porphyrin ligand reduces the degree of nonplanarity in the 16π-electron species relative to the parent 18π complex. Significant high-field shifts of the (1)H NMR signals of the outer ring protons and large positive values in calculations of nucleus-independent chemical shifts on the central cavity of the porphyrin ring provide unambiguous evidence for the antiaromatic character of the 16π Zn(II) species. A combination of magnetic circular dichroism spectroscopic studies and TD-DFT calculations on both the Zn(II) and Cu(II) species demonstrates that the main electronic bands of the dicationic species can be readily assigned by using Michl's 4N perimeter model. Femtosecond transient absorption studies clearly demonstrated that the number of π electrons on the inner ligand perimeter and the configuration of the central metal ion play a critical role in the excited-state relaxation dynamics. Redox potentials for conversion between the 16π, 17π, and 18π systems were measured by cyclic voltammetry in dichloromethane and benzonitrile, and UV/Vis spectra of each oxidation/reduction product were monitored by thin-layer spectroelectrochemistry.

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Section: Resultssupporting

confidence: 53%

Section: Resultsmentioning

confidence: 92%

Synthesis, Characterization, and Spectroscopic Analysis of Antiaromatic Benzofused Metalloporphyrins

Sugawara

Hirata

Kojima

et al. 2012

Chemistry A European J

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“…Thus, the intramolecular rotation is restricted 2c. In addition, the hydrophilic microenvironment around the BDP fluorophore would change to be hydrophobic due to the dehydration of the OEG groups after heating 16d. That is, the polarity around the BDP is greatly decreased.…”

Section: Resultsmentioning

confidence: 99%

BODIPY‐Based Oligo(ethylene glycol) Dendrons as Fluorescence Thermometers: When Thermoresponsiveness Meets Intramolecular Electron/Charge Transfer

Wang

Fan

et al. 2014

Chemistry A European J

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The temperature-dependent photophysical properties of a series of 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene (BODIPY) derivatives with different oligo(ethylene glycol) (OEG) dendrons were investigated. Weak fluorescence emission was observed for these BODIPY derivatives in dilute solution with low viscosity. BDP-G0 and BDP-G1-TEG exhibit a high quantum yield in viscous glycerol solutions, contrary to the moderate and little fluorescence enhancement for BDP-G1 and BDP-G2 under the same conditions. The photoinduced electron transfer (PET) may have quenched the fluorescence, as supported by calculation. Interestingly, the thermoresponsive BODIPY derivatives show heat-induced luminescence enhancement with a high signal-to-noise ratio and their emission maxima are dependent on the structures of branched tri(ethylene glycol) moieties. Finally, preliminary studies on the BODIPY derivatives as intracellular fluorescence indicators in living HeLa cells were carried out.

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“…This indicates a kinetically trapped mesophase separation and a system in a molecularly controlled non-equilibrium state. [44][45][46] These long-lived yet transient states are more polar than the initial state, suggesting that they are formed during cooling by rupture and dissolution of part of the mesostructures. They seem to be a consequence of the crystallization of larger pools of water in the nanostructured water/ IL system.…”

Section: Discussionmentioning

confidence: 99%

Temperature‐Dependent Formation and Transformation of Mesostructures in Water–Ionic Liquid Mixtures

Kattnig

Hinderberger

2012

Chemistry An Asian Journal

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The temperature-dependent formation and transformation of mesostructures in binary mixtures of the ionic liquid (IL) 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim(+)][BF(4)(-)]) and water are characterized. Through addition of nitroxide radicals as paramagnetic spin probes, the temperature dependence of the solution structure can be assessed by using electron paramagnetic resonance (EPR) spectroscopy from typical solutes' points of view. Additionally, the phase behavior on cooling and reheating is probed by differential scanning calorimetry (DSC). Thermal hysteresis and memory effects are observed, and DSC is used to identify the crystallization and thawing of ice as the pertinent phase transition. The EPR data of the nitroxide radicals before and after freezing and thawing reveal a transformation of the mesostructures, probably triggered by the crystallization of water pools to ice. A more polar state results after thawing, thereby suggesting a rupture and dissolution of the ordered IL-rich mesostructures. If the thawed solutions are not agitated, the system relaxes very slowly, that is, at room temperature with a time constant of approximately 90 h, to its equilibrium state of mesophase-separated IL-rich and bulk-like water regions.

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EPR‐Spektroskopische Charakterisierung lokaler nanoskopischer Heterogenitäten beim thermischen Kollaps thermoresponsiver dendronisierter Polymere

Cited by 15 publications

References 54 publications

Synthesis, Characterization, and Spectroscopic Analysis of Antiaromatic Benzofused Metalloporphyrins

Synthesis, Characterization, and Spectroscopic Analysis of Antiaromatic Benzofused Metalloporphyrins

BODIPY‐Based Oligo(ethylene glycol) Dendrons as Fluorescence Thermometers: When Thermoresponsiveness Meets Intramolecular Electron/Charge Transfer

Temperature‐Dependent Formation and Transformation of Mesostructures in Water–Ionic Liquid Mixtures

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