skip to main content


Title: Optical Spin Polarization of a Narrow‐Linewidth Electron‐Spin Qubit in a Chromophore/Stable‐Radical System
Abstract

Photoexcited organic chromophores appended to stable radicals can serve as qubit and/or qudit candidates for quantum information applications. 1,6,7,12‐Tetra‐(4‐tert‐butylphenoxy)‐perylene‐3,4 : 9,10‐bis(dicarboximide) (tpPDI) linked to a partially deuterated α,γ‐bisdiphenylene‐β‐phenylallyl radical (BDPA‐d16) was synthesized and characterized by time‐resolved optical and electron paramagnetic resonance (EPR) spectroscopies. Photoexcitation of tpPDI‐BDPA‐d16results in ultrafast radical‐enhanced intersystem crossing to produce a quartet state (Q) followed by formation of a spin‐polarized doublet ground state (D0). Pulse‐EPR experiments confirmed the spin multiplicity ofQand yielded coherence times ofTm=2.1±0.1 μs and 2.8±0.2 μs forQandD0, respectively. BDPA‐d16eliminates the dominant1H hyperfine couplings, resulting in a single narrow line for both theQandD0states, which enhances the spectral resolution needed for good qubit addressability.

 
more » « less
NSF-PAR ID:
10393310
Author(s) / Creator(s):
 ;  ;  ;  ;  ;  ;  ;  
Publisher / Repository:
Wiley Blackwell (John Wiley & Sons)
Date Published:
Journal Name:
Angewandte Chemie
Volume:
135
Issue:
6
ISSN:
0044-8249
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. Abstract

    Photoexcited organic chromophores appended to stable radicals can serve as qubit and/or qudit candidates for quantum information applications. 1,6,7,12‐Tetra‐(4‐tert‐butylphenoxy)‐perylene‐3,4 : 9,10‐bis(dicarboximide) (tpPDI) linked to a partially deuterated α,γ‐bisdiphenylene‐β‐phenylallyl radical (BDPA‐d16) was synthesized and characterized by time‐resolved optical and electron paramagnetic resonance (EPR) spectroscopies. Photoexcitation of tpPDI‐BDPA‐d16results in ultrafast radical‐enhanced intersystem crossing to produce a quartet state (Q) followed by formation of a spin‐polarized doublet ground state (D0). Pulse‐EPR experiments confirmed the spin multiplicity ofQand yielded coherence times ofTm=2.1±0.1 μs and 2.8±0.2 μs forQandD0, respectively. BDPA‐d16eliminates the dominant1H hyperfine couplings, resulting in a single narrow line for both theQandD0states, which enhances the spectral resolution needed for good qubit addressability.

     
    more » « less
  2. Abstract

    We report on the largest open‐shell graphenic bilayer and also the first example of triply negatively charged radical π‐dimer. Upon three‐electron reduction, bilayer nanographene fragment molecule (C96H24Ar6)2(Ar=2,6‐dimethylphenyl) (12) was transformed to a triply negatively charged species123, which has been characterized by single‐crystal X‐ray diffraction, electron paramagnetic resonance (EPR) spectroscopy and magnetic properties on a superconducting quantum interference device (SQUID).123features a 96‐center‐3‐electron (96c/3e) pancake bond with a doublet ground state, which can be thermally excited to a quartet state. It consists of 34 π‐fused rings with 96 conjugatedsp2carbon atoms. Spin frustration is observed with the frustration parameterf>31.8 at low temperatures in123, which indicates graphene upon reduction doping may behave as a quantum spin liquid.

     
    more » « less
  3. Abstract

    We report on the largest open‐shell graphenic bilayer and also the first example of triply negatively charged radical π‐dimer. Upon three‐electron reduction, bilayer nanographene fragment molecule (C96H24Ar6)2(Ar=2,6‐dimethylphenyl) (12) was transformed to a triply negatively charged species123.−, which has been characterized by single‐crystal X‐ray diffraction, electron paramagnetic resonance (EPR) spectroscopy and magnetic properties on a superconducting quantum interference device (SQUID).123.−features a 96‐center‐3‐electron (96c/3e) pancake bond with a doublet ground state, which can be thermally excited to a quartet state. It consists of 34 π‐fused rings with 96 conjugatedsp2carbon atoms. Spin frustration is observed with the frustration parameterf>31.8 at low temperatures in123.−, which indicates graphene upon reduction doping may behave as a quantum spin liquid.

     
    more » « less
  4. Abstract

    Reduction of the cobalt(II) chloride complex, Ph2B(tBuIm)2Co(THF)Cl (1) in the presence oftBuN≡C affords the diamagnetic, square planar cobalt(I) complex Ph2B(tBuIm)2Co(C≡NtBu)2(2). This is a rare example of a 16‐electron cobalt(I) complex that is structurally related to square planar noble metal complexes. Accordingly, the electronic structure of2, as calculated by DFT, reveals that the HOMO is largely dz2in character. Complex2is readily oxidized to its cobalt(II) congener [Ph2B(tBuIm)2Co(C=NtBu)2]BPh4(3‐BPh4), whose EPR spectral parameters are characteristic of low‐spin d7with an unpaired electron in an orbital of dz2parentage. This is also consistent with the results of DFT calculations. Despite its 16‐electron configuration and the dz2parentage of the HOMO, the only tractable reactions of2involve one electron oxidation to afford3.

     
    more » « less
  5. Abstract

    Large separation of magnetic levels and slow relaxation in metal complexes are desirable properties of single‐molecule magnets (SMMs). Spin‐phonon coupling (interactions of magnetic levels with phonons) is ubiquitous, leading to magnetic relaxation and loss of memory in SMMs and quantum coherence in qubits. Direct observation of magnetic transitions and spin‐phonon coupling in molecules is challenging. We have found that far‐IR magnetic spectra (FIRMS) of Co(PPh3)2X2(Co‐X; X=Cl, Br, I) reveal rarely observed spin‐phonon coupling as avoided crossings between magnetic andu‐symmetry phonon transitions. Inelastic neutron scattering (INS) gives phonon spectra. Calculations using VASP and phonopy programs gave phonon symmetries and movies. Magnetic transitions among zero‐field split (ZFS) levels of theS=3/2 electronic ground state were probed by INS, high‐frequency and ‐field EPR (HFEPR), FIRMS, and frequency‐domain FT terahertz EPR (FD‐FT THz‐EPR), giving magnetic excitation spectra and determining ZFS parameters (D, E) andgvalues. Ligand‐field theory (LFT) was used to analyze earlier electronic absorption spectra and give calculated ZFS parameters matching those from the experiments. DFT calculations also gave spin densities inCo‐X, showing that the larger Co(II) spin density in a molecule, the larger its ZFS magnitude. The current work reveals dynamics of magnetic and phonon excitations in SMMs. Studies of such couplings in the future would help to understand how spin‐phonon coupling may lead to magnetic relaxation and develop guidance to control such coupling.

     
    more » « less