Spin dynamics of photogenerated triradicals in fixed distance electron donor - Chromophore - Acceptor - TEMPO molecules

Qixi Mi, Erin T. Chernick, David W. McCamant, Emily A Weiss, Mark A Ratner, Michael R Wasielewski

Research output: Contribution to journalArticle

27 Citations (Scopus)

Abstract

The stable free radical 2,2,6,6-tetramethylpiperidinoxyl (TEMPO, T .) was covalently attached to the electron acceptor in a donor-chromophore-acceptor (D-C-A) system, MeOAn-6ANI-Ph n-A-T ., having well-defined distances between each component, where MeOAn = p-methoxyaniline, 6ANI = 4-(N-piperidinyl)-naphthalene-1,8-dicarboximide, Ph = 2,5-dimethylphenyl (n = 0,1), and A = naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI). Using both time-resolved optical and EPR spectroscopy, we show that T . influences the spin dynamics of the photogenerated triradical states 2,4(MeOAn +.-6ANI-Ph n- A- .T .), resulting in modulation of the charge recombination rate within the triradical compared with the corresponding biradical lacking T .. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn +. and A -. is not altered by the presence of T ., which interacts most strongly with A -. and accelerates radical pair intersystem crossing. Charge recombination within the triradicals results in the formation of 2,4(MeOAn-6ANI-Ph n- 3*NI-T .) or 2,4(MeOAn- 3*6ANI-Ph n-PI-T .) in which T . is strongly spin polarized in emission. Normally, the spin dynamics of correlated radical pairs do not produce a net spin polarization; however, the rate at which the net spin polarization appears on T . closely follows the photogenerated radical ion pair decay rate. This effect is attributed to antiferromagnetic coupling between T . and the local triplet state 3*NI, which is populated following charge recombination. These results are explained using a switch in the spin basis set between the triradical and the three-spin charge recombination product having both T . and 3*NI or 3*6ANI present.

Original languageEnglish
Pages (from-to)7323-7333
Number of pages11
JournalJournal of Physical Chemistry A
Volume110
Issue number23
DOIs
Publication statusPublished - Jun 15 2006

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Spin dynamics
Spin polarization
Chromophores
spin dynamics
chromophores
Molecules
Electrons
Exchange interactions
Free Radicals
Paramagnetic resonance
molecules
electrons
Switches
Modulation
Spectroscopy
Ions
naphthalene
spin exchange
polarization
free radicals

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

Spin dynamics of photogenerated triradicals in fixed distance electron donor - Chromophore - Acceptor - TEMPO molecules. / Mi, Qixi; Chernick, Erin T.; McCamant, David W.; Weiss, Emily A; Ratner, Mark A; Wasielewski, Michael R.

In: Journal of Physical Chemistry A, Vol. 110, No. 23, 15.06.2006, p. 7323-7333.

Research output: Contribution to journalArticle

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abstract = "The stable free radical 2,2,6,6-tetramethylpiperidinoxyl (TEMPO, T .) was covalently attached to the electron acceptor in a donor-chromophore-acceptor (D-C-A) system, MeOAn-6ANI-Ph n-A-T ., having well-defined distances between each component, where MeOAn = p-methoxyaniline, 6ANI = 4-(N-piperidinyl)-naphthalene-1,8-dicarboximide, Ph = 2,5-dimethylphenyl (n = 0,1), and A = naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI). Using both time-resolved optical and EPR spectroscopy, we show that T . influences the spin dynamics of the photogenerated triradical states 2,4(MeOAn +.-6ANI-Ph n- A- .T .), resulting in modulation of the charge recombination rate within the triradical compared with the corresponding biradical lacking T .. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn +. and A -. is not altered by the presence of T ., which interacts most strongly with A -. and accelerates radical pair intersystem crossing. Charge recombination within the triradicals results in the formation of 2,4(MeOAn-6ANI-Ph n- 3*NI-T .) or 2,4(MeOAn- 3*6ANI-Ph n-PI-T .) in which T . is strongly spin polarized in emission. Normally, the spin dynamics of correlated radical pairs do not produce a net spin polarization; however, the rate at which the net spin polarization appears on T . closely follows the photogenerated radical ion pair decay rate. This effect is attributed to antiferromagnetic coupling between T . and the local triplet state 3*NI, which is populated following charge recombination. These results are explained using a switch in the spin basis set between the triradical and the three-spin charge recombination product having both T . and 3*NI or 3*6ANI present.",
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T1 - Spin dynamics of photogenerated triradicals in fixed distance electron donor - Chromophore - Acceptor - TEMPO molecules

AU - Mi, Qixi

AU - Chernick, Erin T.

AU - McCamant, David W.

AU - Weiss, Emily A

AU - Ratner, Mark A

AU - Wasielewski, Michael R

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N2 - The stable free radical 2,2,6,6-tetramethylpiperidinoxyl (TEMPO, T .) was covalently attached to the electron acceptor in a donor-chromophore-acceptor (D-C-A) system, MeOAn-6ANI-Ph n-A-T ., having well-defined distances between each component, where MeOAn = p-methoxyaniline, 6ANI = 4-(N-piperidinyl)-naphthalene-1,8-dicarboximide, Ph = 2,5-dimethylphenyl (n = 0,1), and A = naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI). Using both time-resolved optical and EPR spectroscopy, we show that T . influences the spin dynamics of the photogenerated triradical states 2,4(MeOAn +.-6ANI-Ph n- A- .T .), resulting in modulation of the charge recombination rate within the triradical compared with the corresponding biradical lacking T .. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn +. and A -. is not altered by the presence of T ., which interacts most strongly with A -. and accelerates radical pair intersystem crossing. Charge recombination within the triradicals results in the formation of 2,4(MeOAn-6ANI-Ph n- 3*NI-T .) or 2,4(MeOAn- 3*6ANI-Ph n-PI-T .) in which T . is strongly spin polarized in emission. Normally, the spin dynamics of correlated radical pairs do not produce a net spin polarization; however, the rate at which the net spin polarization appears on T . closely follows the photogenerated radical ion pair decay rate. This effect is attributed to antiferromagnetic coupling between T . and the local triplet state 3*NI, which is populated following charge recombination. These results are explained using a switch in the spin basis set between the triradical and the three-spin charge recombination product having both T . and 3*NI or 3*6ANI present.

AB - The stable free radical 2,2,6,6-tetramethylpiperidinoxyl (TEMPO, T .) was covalently attached to the electron acceptor in a donor-chromophore-acceptor (D-C-A) system, MeOAn-6ANI-Ph n-A-T ., having well-defined distances between each component, where MeOAn = p-methoxyaniline, 6ANI = 4-(N-piperidinyl)-naphthalene-1,8-dicarboximide, Ph = 2,5-dimethylphenyl (n = 0,1), and A = naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI). Using both time-resolved optical and EPR spectroscopy, we show that T . influences the spin dynamics of the photogenerated triradical states 2,4(MeOAn +.-6ANI-Ph n- A- .T .), resulting in modulation of the charge recombination rate within the triradical compared with the corresponding biradical lacking T .. The observed spin-spin exchange interaction between the photogenerated radicals MeOAn +. and A -. is not altered by the presence of T ., which interacts most strongly with A -. and accelerates radical pair intersystem crossing. Charge recombination within the triradicals results in the formation of 2,4(MeOAn-6ANI-Ph n- 3*NI-T .) or 2,4(MeOAn- 3*6ANI-Ph n-PI-T .) in which T . is strongly spin polarized in emission. Normally, the spin dynamics of correlated radical pairs do not produce a net spin polarization; however, the rate at which the net spin polarization appears on T . closely follows the photogenerated radical ion pair decay rate. This effect is attributed to antiferromagnetic coupling between T . and the local triplet state 3*NI, which is populated following charge recombination. These results are explained using a switch in the spin basis set between the triradical and the three-spin charge recombination product having both T . and 3*NI or 3*6ANI present.

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