Picosecond absorption studies of photoinduced charge separation in polyelectrolyte bound aromatic chromophores

Shand, Mark A.; Rodgers, Michael A. J.; Webber, S. E.

doi:10.1016/0009-2614(91)90167-8

Cited by 6 publications

(8 citation statements)

References 13 publications

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“…At low fluences of excitation (<10 mJ cm -2 pulse -1 ), we did not observe any reduction of the MV 2+ ions accompanying the quenching of the fluorescence (data not shown). These results may be understood in terms of the observations of Rodgers and co-workers 30 who showed that nonfluorescent ground-state complexes are formed between MV 2+ and pyrenyl residues bound covalently to poly(methacrylic acid); the fluorescence of the pyrenyl residues is quenched by MV 2+ via an electron transfer mechanism within <20 ps of excitation, but radical ion products are not observed presumably because of their rapid recombination in these bimolecular complexes . A similar mechanism probably accounts for the quenching of the fluorescence of the pyrenyl residues in BPDE-modified DNA (Figure ) and a lack of formation of MV •+ radical cation products at low laser pulse fluences.…”

Section: Resultsmentioning

confidence: 57%

“…The coincidence of the rates of disappearance of the hydrated electrons and the rate of appearance of MV •+ suggests that the latter are formed via diffusive bimolecular encounters between hydrated electrons and MV 2+ . The reduction of methylviologen by hydrated electrons in aqueous solutions has been observed previously − and was not further investigated in this work.…”

Section: Resultsmentioning

confidence: 87%

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Migration and Trapping of Photoinjected Excess Electrons in Double-Stranded B-Form DNA But Not in Single-Stranded DNA

et al. 1997

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Photoexcitation of a pyrene derivative covalently bound to double-stranded calf thymus DNA with 355 nm Nd:YAG laser pulses (fwhm ) 24 ps, 50 mJ/cm 2 /pulse) results in the efficient two-photon-induced ionization of the pyrenyl residues. By use of nanosecond transient absorption techniques, it is shown that the excess electrons injected into the DNA can reduce methylviologen cations (MV 2+ ) that are noncovalently bound to the DNA but not MV 2+ in the outer aqueous solution phase. In double-stranded DNA, this reduction of MV 2+ to MV •+ occurs via two kinetic phases, a rapid one that is complete within e7 ns and a slower one (200-300 ns) due to the diffusive reduction of MV 2+ by hydrated electrons. The appearance of the first, rapid reduction phase of MV 2+ depends on the secondary structure of the DNA, since it is observed only in the double-stranded form but not in the denatured, single-stranded form. This rapid reduction phase is entirely eliminated upon the addition of magnesium ions, which displace the positively charged MV 2+ cations from the double-stranded DNA molecules. By variation of the concentration of MV 2+ cations at a constant distribution of covalently bound pyrenyl residues (60 base pairs per pyrenyl residue), a mean distance of migration of excess electrons in double-stranded DNA of ca. 40 Å is estimated.

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Section: Resultsmentioning

confidence: 57%

Section: Resultsmentioning

confidence: 87%

Migration and Trapping of Photoinjected Excess Electrons in Double-Stranded B-Form DNA But Not in Single-Stranded DNA

et al. 1997

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“…[8][9][10][11] This earlier work reports a consistent increase in charge-separated yield with a decrease in pH which is ascribed to increased "hydrophobic protection" (which is equivalent to the term "compartmentalization", discussed above). Hsiao and Webber 12 also demonstrated this effect by preferential adsorption of chromophores covalently attached to PMA onto water-soluble polystyrene latex particles.…”

Section: Introductionmentioning

confidence: 69%

“…We and others have been involved in the study of photoinduced charge separation between viologens and polyelectrolyte bound aromatic chromophores, particularly poly(methacrylic acid), PMA, with anthracene chromophores. − This earlier work reports a consistent increase in charge-separated yield with a decrease in pH which is ascribed to increased “hydrophobic protection” (which is equivalent to the term “compartmentalization”, discussed above). Hsiao and Webber also demonstrated this effect by preferential adsorption of chromophores covalently attached to PMA onto water-soluble polystyrene latex particles.…”

Section: Introductionmentioning

confidence: 98%

Photoinduced Electron Transfer at the Core/Shell Interface of Polystyrene−Anthracene−Poly(methacrylic acid) Diblock Copolymer Micelles in Aqueous Media

1997

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We have characterized the photophysics and excited-state electron transfer reactions of polymer micelles formed from diblock polystyrene-(anthracene)-block-poly(methacrylic acid). In these studies (anthracene) comprises either a single 1-(2-anthryl)-1-phenylethylene (An) or an average of two vinyl-9,10-diphenylanthracene (vDPA). This architecture is expected to place the chromophores in the interfacial region between the polystyrene core and poly(methacrylic acid) corona. Quenching of the anthryl fluorescence by Tl + and two viologens (SPV, 4,4′-bipyridyl-1,1′-bis(propanesulfonate), and MV 2+ , methyl viologen) demonstrated that access to these chromophores was limited at all pHs, and the rate of diffusion of the viologens was relatively slow. Similar conclusions were drawn from quenching of the 3 An* state and the anion radical SPV •-by O 2 . We believe this illustrates that the interfacial region of the micelle is not fully deprotonated even at pH 9. It was observed that the fraction of 3 An* that was quenched by SPV was smaller than 1 An*. This demonstrates the existence of a heterogeneous distribution of anthryl sites such that some 3 An* cannot be quenched, which is not the case for 1 An*. We conclude that the spatial requirements for quenching these two excited states are not equivalent. Electron transfer quenching by SPV produces SPV •-that is very longlived, but some unknown reaction removes the anthryl cation radical. As a consequence, we can build up a concentration of SPV •-under steady-state photolysis. The quantum yield of charge separation per quenching event is similar to previous cases we have studied, ca. 0.5, but unlike linear polyacids, there is very little pH dependence. This is consistent with the idea that there is minimal deprotonation near the core-corona interface of the micelle.

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“…The basic features of the pumpprobe double-diode array spectrography and the single-wavelength kinetic setup have been described. [5][6] The convolution of excitation and probe pulses in collinear geometry for single-exponential processes yielded a response time of ca. 10 ps.…”

Section: Methodsmentioning

confidence: 99%

Laser flash photolysis studies of the contact complex between molecular oxygen and 1-methylnaphthalene

Logunov¹,

Rodgers²

1993

J. Phys. Chem.

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The contact complex (3%) between 1 -methylnaphthalene (MN) and molecular oxygen in several solvents was excited at 355 nm, and the subsequent processes were observed by absorption spectrometry on subnanosecond and suprananosecond time scales. Experimental evidence for a significant amount of charge-transfer character in the upper 3E2 is presented. The lifetime of this charge-transfer state (CT) is 20 f 10 ps, and there are two competitive pathways for decay of this radical pair: (i) to the localized triplet state and (ii) to the triplet ground state. In the nonpolar solvent cyclohexane, decay to the localized triplet state dominates and CPT = 1; in the polar solvent acetonitrile, the competition between two recombination pathways is approximately equal and reduces the quantum yield of the triplet state to one-half. The quantum yields of singlet oxygen (02(lAg)) in the two solvents reflect these triplet yields, which indicates that the precursor of singlet oxygen is the free triplet state of MN. This is supported by kinetic evidence. There is no evidence that intersystem crossing in the CT state results in direct entry to the singlet manifold.

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Picosecond absorption studies of photoinduced charge separation in polyelectrolyte bound aromatic chromophores

Cited by 6 publications

References 13 publications

Migration and Trapping of Photoinjected Excess Electrons in Double-Stranded B-Form DNA But Not in Single-Stranded DNA

Migration and Trapping of Photoinjected Excess Electrons in Double-Stranded B-Form DNA But Not in Single-Stranded DNA

Photoinduced Electron Transfer at the Core/Shell Interface of Polystyrene−Anthracene−Poly(methacrylic acid) Diblock Copolymer Micelles in Aqueous Media

Laser flash photolysis studies of the contact complex between molecular oxygen and 1-methylnaphthalene

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