Electron Spin Polarization Transfer from a Nitroxide Incarcerated within a Nanocapsule to a Nitroxide in the Bulk Aqueous Solution

Jockusch, Steffen; Zeika, Olaf; Nithyanandhan, Jayaraj; Ramamurthy, V.; Turro, Nicholas J.

doi:10.1021/jz101006s

Cited by 35 publications

(36 citation statements)

References 19 publications

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“…32-276 ms), [38,39,45] which is reasonable because the triplets tate localized on the NDI can be quenched by the stable radical. [23,26,46] This is also proved by measuring the ns TA spectra of NDI-Phw ith increasing concentrations of Ph-Vz (Supporting Information, Figure S31). We observed that with the increasing concentration of Ph-Vz, the triplet lifetimeo fN DI-Phd ecreased from 114.2 msto4 0.2 ms.…”

Section: Observation Of the Triplet Excited State With Nanosecond Tramentioning

confidence: 62%

“…The observed lifetime of the triplet state of the NDI unit in the current dyads is much shorter than the intrinsic triplet state lifetime of the NDI chromophore (ca. 32–276 μs), which is reasonable because the triplet state localized on the NDI can be quenched by the stable radical . This is also proved by measuring the ns TA spectra of NDI‐Ph with increasing concentrations of Ph‐Vz (Supporting Information, Figure S31).…”

Section: Resultsmentioning

confidence: 99%

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Intersystem Crossing in Naphthalenediimide–Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties

Hussain

Taddei²,

Bussotti³

et al. 2019

Chemistry A European J

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Oxoverdazyl( Vz) radicalu nits were covalently linked to the naphthalenediimide (NDI) chromophore to study the effect of the radicalo nt he photophysical properties, especially the radicale nhanced intersystem crossing (REISC), which is ap romisinga pproach to develop heavyatom-free triplet photosensitizers. Rigid phenylo re thynylphenyll inkers betweent he two moieties were used, thus REISC andf ormation of doublet (D 1 ,t otal spin quantum number S = 1/2) and quartet states (Q 1 , S = 3/2) are anticipated. The photophysical properties of the dyadsw ere studied with steady-statea nd femtosecond/nanosecond transient absorption (TA) spectroscopiesa nd DFT computations. Femtosecond transienta bsorption spectras how af ast electron transfer (< 150 fs), and ISC (ca. 1.4-1.85ps) is induced by charger ecombination (CR, in toluene). Nanosecond transient absorption spectra demonstrated ab iexponential decay of the triplet state of the NDI moiety.T he fast component (lifetime:5 0ns; population ratio:8 0%)i sa ssigned to the D 1 ! D 0 decay,a nd the slow decay component (2.0 ms; 20 %) to the Q 1 !D 0 ISC. DFT computations indicated ferromagnetic interactions between the radicala nd chromophore( J = 0.07-0.13 eV). Reversible formation of the radical aniono ft he NDI moiety by photoreduction of the radical-NDI dyadsi nt he presence of sacrificial electron donor triethanolamine (TEOA) is achieved. This work is useful for design of new triplet photosensitizers based on the REISC effect.

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Section: Observation Of the Triplet Excited State With Nanosecond Tramentioning

confidence: 62%

Section: Resultsmentioning

confidence: 99%

Intersystem Crossing in Naphthalenediimide–Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties

Hussain

Taddei²,

Bussotti³

et al. 2019

Chemistry A European J

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“…Excitation of 2@OA 2 with laser pulses (355 nm, 5 ns pulse width) generated the transient absorption spectrum shown in Figure 1 (left). This transient absorption with a maximum at 650 nm was assigned to the triplet state of 2 based on previous experiments in acetonitrile solution 8 and similarities with unsubstituted thioxanthone. 9 However, the triplet lifetime of 2 is strongly reduced (91 ns) in OA complexes compared to that in acetonitrile solutions (12 μs).…”

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confidence: 69%

CIDEP from a Polarized Ketone Triplet State Incarcerated within a Nanocapsule to a Nitroxide in the Bulk Aqueous Solution

Jockusch

Porel

Ramamurthy

et al. 2011

J. Phys. Chem. Lett.

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b S Supporting Information S table free radicals, such as nitroxides, are known to efficiently quench photoexcited triplet states of organic molecules. 1 Recently, we have shown that this quenching also occurs, although at a slower rate, if the photoexcited ketone is incarcerated inside of an organic container (octa acid) that separates the excited-state ketone and nitroxide by a molecular wall. 2 For this study, we used the cavitand termed "octa acid" (OA, Chart 1), which is known to incarcerate nonpolar molecules by forming a complex in aqueous solutions at basic pH. 3 It was established that relatively nonpolar ketones, such as 4,4 0 -dimethyl benzil (1, Chart 1), form a 2:1 complex with OA, where two OA molecules encapsulate one molecule of 1 (1@OA 2 ). 4 The ketone 1 shows room-temperature phosphorescence with a lifetime of 596 μs when encapsulated inside of OA. 2 The phosphorescence of 1@OA 2 was quenched efficiently by a positively charged nitroxide (Tx, Chart 1) with a rate constant of 1.5 Â 10 9 M À1 s À1 . We rationalized this high rate constant with the involvement of electrostatic attractions of the positively charged quencher (Tx) and the negatively charged external surface of the OA capsule. No quenching of the phosphorescence of 1@OA 2 was observed by the negatively charged nitroxide (TQ, Chart 1) under our experimental conditions, which was rationalized by electrostatic repulsion between incarcerated 1 and TQ. The upper limit for the rate constant of this quenching was estimated to be ∼10 5 M À1 s À1 , which is 4 orders of magnitude lower than the rate constant for quenching by Tx. 2 The quenching of triplet states of ketones by nitroxides often generates spin-polarized nitroxides, which had been observed by time-resolved electron paramagnetic resonance (TR-EPR) spectroscopy. 5À7 In these studies, the triplet quenching and spin polarization occurred during collisions of freely diffusing ketones and nitroxides or with the nitroxide that was covalently linked to the ketone. In this Letter, we investigate whether spin polarization of nitroxides is also observable in quenching processes, where the triplet ketone and the nitroxide are separated by a molecular wall (OA).As ketones, we selected 4,4 0 -dimethyl benzil (1) and the thioxanthone derivative 2 (Chart 1). Both ketones have been shown to form 2:1 complexes with OA. 2,8 Efficient triplet quenching of 1@OA 2 by Tx has been demonstrated by phosphorescence measurements. 2 Because 2@OA 2 did not show measurable phosphoresce at room temperature, laser flash photolysis experiments were performed to establish the quenching efficiency of 2@OA 2 triplet states by Tx. Excitation of 2@OA 2 with laser pulses (355 nm, 5 ns pulse width) generated the transient absorption spectrum shown in Figure 1 (left). This transient absorption with a maximum at 650 nm was assigned to the triplet state of 2 based on previous experiments in acetonitrile solution 8 and similarities with unsubstituted thioxanthone. 9 However, the triplet lifetime of 2 is strongly reduced (91 n...

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“…Quaternary RAPID COMMUNICATION ammonium-2,2,6,6-tetramethyl-1-piperidinyloxy (Q-TEMPO) synthesized according to the literature procedure. 30 Other solvents were purified by conventional drying and distillation procedures.…”

Section: Methodsmentioning

confidence: 99%

Polystyrene/clay nanocomposites by atom transfer radical nitroxide coupling chemistry

Aydın

Taşdelen

Uyar

et al. 2012

J. Polym. Sci. A Polym. Chem.

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During the last two decades, the introduction of welldispersed clay layers such as montmorillonite (MMT) into a polymer matrix has been proved to be extremely effective in the improvement of mechanical, thermal, and barrier properties of the polymers.1 However, the dispersion of clay as individual platelets throughout the polymer is difficult to achieve due to strong van der Waals forces holding platelets together in conjunction with the incompatibility of the hydrophilic clay with the organophilic (hydrophobic) polymer matrix, giving way to clay agglomeration. Thus, the surface of the clays is commonly modified with a cation exchange technique to expand basal spacing and make the layered silicate compatible with polymer matrixes. Currently polymer/clay nanocomposites can be prepared by three ways such as solution mixing, melt blending, and in situ polymerization.2 In the solution mixing method, the polymer is dissolved in an organic solvent, then the clay is dispersed in the obtained solution, and subsequently, either the solvent is evaporated or the polymer precipitated. However, the large quantities of volatile solvent necessary for this approach make it less attractive as an industrial process. Melt blending is a solvent-free method to enable mixing of the layered silicate with the polymer matrix in the molten state. However, very careful attention has to be paid to finely tune the processing conditions to increase the compatibility of clay layer surfaces with the polymer matrix. 3 In the in situ polymerization technique, the monomer, together with the initiator and/or catalyst, is intercalated within the silicate layers and the polymerization is initiated by external stimulation such as thermal, photochemical, or chemical activation. [4][5][6][7][8][9][10][11][12][13][14][15][16] The chain growth in the clay galleries triggers the clay exfoliation and, hence, the nanocomposite formation.

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Electron Spin Polarization Transfer from a Nitroxide Incarcerated within a Nanocapsule to a Nitroxide in the Bulk Aqueous Solution

Cited by 35 publications

References 19 publications

Intersystem Crossing in Naphthalenediimide–Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties

Intersystem Crossing in Naphthalenediimide–Oxoverdazyl Dyads: Synthesis and Study of the Photophysical Properties

CIDEP from a Polarized Ketone Triplet State Incarcerated within a Nanocapsule to a Nitroxide in the Bulk Aqueous Solution

Polystyrene/clay nanocomposites by atom transfer radical nitroxide coupling chemistry

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