Photoinduced electron spin polarization (ESP) is reported in the electronic ground states of three Pt(II) complexes comprised of two S = 1/2 nitronyl nitroxide (NN) radicals attached through different length -phenylethynyl bridges to the 3,6 positions of a catecholate (CAT, donor) and 4,4'-di--butyl-2,2'-bipyridine (bpy, acceptor). Complexes - have from 17 to 41 bonds separating NN radicals and display cw-EPR spectra consistent with || ≫ ||, || ≥ ||, and || < ||, respectively, where is the magnetic exchange coupling between NN radicals in the electronic ground state, and is the isotropic N hyperfine coupling constant. Light-induced transient EPR spectra characterized as enhanced ground-state absorption were observed for all three complexes using 532 nm pulsed laser excitation into the ligand-to-ligand charge transfer (LL'CT) band of the (CAT)Pt(bpy) chromophore. The magnitude of the observed ESP increases in the order < < and is inversely correlated with the magnitude of ground-state . In addition to the experimental observation of net absorptive polarization in -, light excitation also produces multiplet polarization in . Since the weak dipolar coupling leads to a strong spectral overlap of the absorptive and emissive components, the multiplet polarization is not observed in and and is very weak in . The ability to spin-polarize multiple radical spins with a single photon is anticipated to advance new photoinduced multi qubit/qudit ESP protocols for quantum information science applications.

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http://dx.doi.org/10.1021/jacs.4c00930DOI Listing

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