Abstract
Photoexcitation of electron donor-acceptor molecules frequently produces radical ion pairs with well-defined initial spin-polarized states that have attracted significant interest for spintronics. Transfer of this initial spin polarization to a stable radical is predicted to depend on the rates of the radical ion pair recombination reactions, but this prediction has not been tested experimentally. In this study, a stable radical/electron donor/chromophore/electron acceptor molecule, BDPA•-mPD-ANI-NDI, where BDPA• is α,γ-bisdiphenylene-β-phenylallyl, mPD is m-phenylenediamine, ANI is 4-aminonaphthalene-1,8-dicarboximide, and NDI is naphthalene-1,4:5,8-bis(dicarboximide), was synthesized. Photoexcitation of ANI produces the triradical BDPA•-mPD+•-ANI-NDI-• in which the mPD+•-ANI-NDI-• radical ion pair is spin coupled to the BDPA• stable radical. BDPA•-mPD+•-ANI-NDI-• and its counterpart lacking the stable radical are found to exhibit spin-selective charge recombination in which the triplet radical ion pair 3(mPD+•-ANI-NDI-•) is in equilibrium with the 3∗NDI charge recombination product. Time-resolved EPR measurements show that this process is associated with an inversion of the sign of the polarization transferred to BDPA• over time. The polarization transfer rates are found to be strongly solvent dependent, as shifts in this equilibrium affect the spin dynamics. These results demonstrate that even small changes in electron transfer dynamics can have a large effect on the spin dynamics of photogenerated multispin systems.
| Original language | English (US) |
|---|---|
| Pages (from-to) | 4455-4463 |
| Number of pages | 9 |
| Journal | Journal of Physical Chemistry A |
| Volume | 121 |
| Issue number | 23 |
| DOIs | |
| State | Published - Jun 15 2017 |
Funding
This work was supported by the National Science Foundation, Grant No. CHE-1565925. N.E.H. thanks the Department of Energy, Office of Science, Graduate Fellowship Program, for a fellowship. This research is supported in part by the Department of Energy, Office of Science, Graduate Fellowship Program (DOE SCGF), made possible in part by the American Recovery and Reinvestment Act of 2009, administered by ORISE-ORAU under Contract No. DE-AC05-06OR23100. This work made use of the IMSERC at Northwestern University, which has received support from the Soft and Hybrid Nanotechnology Experimental (SHyNE) Resource (NSF NNCI-1542205), the State of Illinois, and the International Institute for Nanotechnology (IIN).
ASJC Scopus subject areas
- Physical and Theoretical Chemistry