Direct measurement of singlet-triplet splitting within rodlike photogenerated radical ion pairs using magnetic field effects: Estimation of the electronic coupling for charge recombination

Research output: Contribution to journalArticle

89 Citations (Scopus)

Abstract

Determining the electronic coupling matrix element, V, for an electron transfer reaction is challenging both experimentally and theoretically. The magnitude of the singlet-triplet splitting (spin-spin exchange interaction), 2J, within a radical ion pair (RP) is directly related to the sum of the squares of the matrix elements that couple the RP state to the ground state and to other energetically proximate excited and ionic states. Each term in this sum is weighted by the reciprocal of the energy gap between the RP state and the particular state to which it is coupled. We present here a series of intramolecular triads with linear, rodlike structures that undergo very efficient two-step electron transfer following direct excitation of a 4-(N-piperidinyl)naphthalene-1,8-dicarboximide (6ANI) chromophore. Attachment of a p-methoxyaniline (MeOAn) donor by means of the piperazine bridge and naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI) acceptors, either directly or through a 2,5-dimethylphenyl (Me2Ph) spacer to 6ANI results in the triads MeOAn-6ANI-NI, MeOAn-6ANI-PI, MeOAn-6ANI-Me2Ph-NI, and MeOAn-6ANI-Me2Ph-PI. The two-step charge separation from the lowest excited singlet state of 6ANI yields singlet radical ion pairs in which the charges are separated by 14 to 19 Å and whose lifetimes range from about 15 to 200 ns. These lifetimes are long enough such that radical pair intersystem crossing occurs to form the triplet radical ion pair, which then recombines to form the ground state and a neutral excited triplet state, which is localized either on 6ANI or NI. The yield of this locally excited triplet state, monitored by nanosecond transient absorption as a function of applied magnetic field strength, exhibits distinct resonances that directly yield 2J. The value of 2J is used to estimate VCR for charge recombination of the radical ion pair. These measurements provide a highly sensitive method of determining the dependence of the electronic coupling on the structure of the radical ion pair.

Original languageEnglish
Pages (from-to)3639-3647
Number of pages9
JournalJournal of Physical Chemistry A
Volume107
Issue number19
DOIs
Publication statusPublished - May 15 2003

Fingerprint

Magnetic field effects
Ions
electronics
magnetic fields
Excited states
ions
Ground state
naphthalene
atomic energy levels
electron transfer
Videocassette recorders
excitation
Electrons
Exchange interactions
life (durability)
Chromophores
ground state
spin exchange
polarization (charge separation)
matrices

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry

Cite this

@article{7a6182eba35140ae85adbdc3006e8270,
title = "Direct measurement of singlet-triplet splitting within rodlike photogenerated radical ion pairs using magnetic field effects: Estimation of the electronic coupling for charge recombination",
abstract = "Determining the electronic coupling matrix element, V, for an electron transfer reaction is challenging both experimentally and theoretically. The magnitude of the singlet-triplet splitting (spin-spin exchange interaction), 2J, within a radical ion pair (RP) is directly related to the sum of the squares of the matrix elements that couple the RP state to the ground state and to other energetically proximate excited and ionic states. Each term in this sum is weighted by the reciprocal of the energy gap between the RP state and the particular state to which it is coupled. We present here a series of intramolecular triads with linear, rodlike structures that undergo very efficient two-step electron transfer following direct excitation of a 4-(N-piperidinyl)naphthalene-1,8-dicarboximide (6ANI) chromophore. Attachment of a p-methoxyaniline (MeOAn) donor by means of the piperazine bridge and naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI) acceptors, either directly or through a 2,5-dimethylphenyl (Me2Ph) spacer to 6ANI results in the triads MeOAn-6ANI-NI, MeOAn-6ANI-PI, MeOAn-6ANI-Me2Ph-NI, and MeOAn-6ANI-Me2Ph-PI. The two-step charge separation from the lowest excited singlet state of 6ANI yields singlet radical ion pairs in which the charges are separated by 14 to 19 {\AA} and whose lifetimes range from about 15 to 200 ns. These lifetimes are long enough such that radical pair intersystem crossing occurs to form the triplet radical ion pair, which then recombines to form the ground state and a neutral excited triplet state, which is localized either on 6ANI or NI. The yield of this locally excited triplet state, monitored by nanosecond transient absorption as a function of applied magnetic field strength, exhibits distinct resonances that directly yield 2J. The value of 2J is used to estimate VCR for charge recombination of the radical ion pair. These measurements provide a highly sensitive method of determining the dependence of the electronic coupling on the structure of the radical ion pair.",
author = "Weiss, {Emily A} and Ratner, {Mark A} and Wasielewski, {Michael R}",
year = "2003",
month = "5",
day = "15",
doi = "10.1021/jp0224315",
language = "English",
volume = "107",
pages = "3639--3647",
journal = "Journal of Physical Chemistry A",
issn = "1089-5639",
publisher = "American Chemical Society",
number = "19",

}

TY - JOUR

T1 - Direct measurement of singlet-triplet splitting within rodlike photogenerated radical ion pairs using magnetic field effects

T2 - Estimation of the electronic coupling for charge recombination

AU - Weiss, Emily A

AU - Ratner, Mark A

AU - Wasielewski, Michael R

PY - 2003/5/15

Y1 - 2003/5/15

N2 - Determining the electronic coupling matrix element, V, for an electron transfer reaction is challenging both experimentally and theoretically. The magnitude of the singlet-triplet splitting (spin-spin exchange interaction), 2J, within a radical ion pair (RP) is directly related to the sum of the squares of the matrix elements that couple the RP state to the ground state and to other energetically proximate excited and ionic states. Each term in this sum is weighted by the reciprocal of the energy gap between the RP state and the particular state to which it is coupled. We present here a series of intramolecular triads with linear, rodlike structures that undergo very efficient two-step electron transfer following direct excitation of a 4-(N-piperidinyl)naphthalene-1,8-dicarboximide (6ANI) chromophore. Attachment of a p-methoxyaniline (MeOAn) donor by means of the piperazine bridge and naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI) acceptors, either directly or through a 2,5-dimethylphenyl (Me2Ph) spacer to 6ANI results in the triads MeOAn-6ANI-NI, MeOAn-6ANI-PI, MeOAn-6ANI-Me2Ph-NI, and MeOAn-6ANI-Me2Ph-PI. The two-step charge separation from the lowest excited singlet state of 6ANI yields singlet radical ion pairs in which the charges are separated by 14 to 19 Å and whose lifetimes range from about 15 to 200 ns. These lifetimes are long enough such that radical pair intersystem crossing occurs to form the triplet radical ion pair, which then recombines to form the ground state and a neutral excited triplet state, which is localized either on 6ANI or NI. The yield of this locally excited triplet state, monitored by nanosecond transient absorption as a function of applied magnetic field strength, exhibits distinct resonances that directly yield 2J. The value of 2J is used to estimate VCR for charge recombination of the radical ion pair. These measurements provide a highly sensitive method of determining the dependence of the electronic coupling on the structure of the radical ion pair.

AB - Determining the electronic coupling matrix element, V, for an electron transfer reaction is challenging both experimentally and theoretically. The magnitude of the singlet-triplet splitting (spin-spin exchange interaction), 2J, within a radical ion pair (RP) is directly related to the sum of the squares of the matrix elements that couple the RP state to the ground state and to other energetically proximate excited and ionic states. Each term in this sum is weighted by the reciprocal of the energy gap between the RP state and the particular state to which it is coupled. We present here a series of intramolecular triads with linear, rodlike structures that undergo very efficient two-step electron transfer following direct excitation of a 4-(N-piperidinyl)naphthalene-1,8-dicarboximide (6ANI) chromophore. Attachment of a p-methoxyaniline (MeOAn) donor by means of the piperazine bridge and naphthalene-1,8:4,5-bis(dicarboximide) (NI) or pyromellitimide (PI) acceptors, either directly or through a 2,5-dimethylphenyl (Me2Ph) spacer to 6ANI results in the triads MeOAn-6ANI-NI, MeOAn-6ANI-PI, MeOAn-6ANI-Me2Ph-NI, and MeOAn-6ANI-Me2Ph-PI. The two-step charge separation from the lowest excited singlet state of 6ANI yields singlet radical ion pairs in which the charges are separated by 14 to 19 Å and whose lifetimes range from about 15 to 200 ns. These lifetimes are long enough such that radical pair intersystem crossing occurs to form the triplet radical ion pair, which then recombines to form the ground state and a neutral excited triplet state, which is localized either on 6ANI or NI. The yield of this locally excited triplet state, monitored by nanosecond transient absorption as a function of applied magnetic field strength, exhibits distinct resonances that directly yield 2J. The value of 2J is used to estimate VCR for charge recombination of the radical ion pair. These measurements provide a highly sensitive method of determining the dependence of the electronic coupling on the structure of the radical ion pair.

UR - http://www.scopus.com/inward/record.url?scp=0037672769&partnerID=8YFLogxK

UR - http://www.scopus.com/inward/citedby.url?scp=0037672769&partnerID=8YFLogxK

U2 - 10.1021/jp0224315

DO - 10.1021/jp0224315

M3 - Article

AN - SCOPUS:0037672769

VL - 107

SP - 3639

EP - 3647

JO - Journal of Physical Chemistry A

JF - Journal of Physical Chemistry A

SN - 1089-5639

IS - 19

ER -