Electron spin dynamics as a controlling factor for spin-selective charge recombination in donor - Bridge - Acceptor molecules

Tomoaki Miura, Amy M. Scott, Michael R Wasielewski

Research output: Contribution to journalArticle

32 Citations (Scopus)

Abstract

Photoinitiated charge separation and thermal charge recombination (CR) in a covalent donor - bridge - acceptor (D-B-A) system consisting of a perylene-3,4:9,10-bis(dicarboximide) (PDI) acceptor, 2,7-oligofluorene bridge (FLn), and phenothiazine donor (PTZ) (PTZ-FLn-PDI) have been shown to transition from superexchange to charge hopping mechanisms as the D - A distance increases. In work presented here, the spin-selective multiple CR pathways in PTZ-FLn-PDI are studied by a detailed analysis of the magnetic field effect (MFE) on the radical ion pair (RP) lifetime and triplet yield. A kinetic analysis of the MFE gives the spin-selective CR rates and the RP singlet - triplet (S-T) relaxation rates for n = 2-4. When n = 2 and 3, where the S-T splitting (27) of the RP is large, slow S-T relaxation results in a kinetic bottleneck slowing the observed total CR rate at zero magnetic field. These results show that spin state mixing is an important controlling factor for CR reaction rates in these systems. The CR rate constant for the triplet RP (kCRT) obtained by MFE analysis is about 10 times faster than the corresponding rate for the singlet RP (kCRS) when n = 2-4, indicating that kCRT occurs near the maximum of the Marcus rate vs free energy dependence, whereas kCRS is deep in the inverted region. The distance dependence of both kCRS and kCRT is explained by the crossover from superexchange (n = 1 and 2) to distant independent thermal hopping (n = 3 and 4). A possible mechanism of the S-T relaxation is proposed based on S-T dephasing, which may be induced by fluctuations of 2J resulting from bridge torsional dynamics.

Original languageEnglish
Pages (from-to)20370-20379
Number of pages10
JournalJournal of Physical Chemistry C
Volume114
Issue number48
DOIs
Publication statusPublished - Dec 9 2010

Fingerprint

Spin dynamics
spin dynamics
electron spin
Magnetic field effects
Ions
phenothiazines
Molecules
Electrons
molecules
ions
magnetic fields
Perylene
Kinetics
recombination reactions
Free energy
kinetics
Reaction rates
polarization (charge separation)
Rate constants
Magnetic fields

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

Cite this

Electron spin dynamics as a controlling factor for spin-selective charge recombination in donor - Bridge - Acceptor molecules. / Miura, Tomoaki; Scott, Amy M.; Wasielewski, Michael R.

In: Journal of Physical Chemistry C, Vol. 114, No. 48, 09.12.2010, p. 20370-20379.

Research output: Contribution to journalArticle

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