Co-reporter: Martin L. Kirk, David A. Shultz, Diana Habel-Rodriguez, Robert D. Schmidt, and Ubie Sullivan
pp: 14712-14716
Publication Date(Web):June 16, 2010
DOI: 10.1021/jp102955j
Computations and EPR spectroscopy are used to probe the spin distribution of donor−bridge−acceptor (D−B−A) biradical complexes: TpCum,MeZn(SQ-NN) (1), TpCum,MeZn(SQ-1,4-Ph-NN) (2), TpCum,MeZn(SQ-2,5-TP-NN) (3), and TpCum,MeZn(SQ-2,5-Xyl-NN) (4) (SQ = orthosemiquinone and NN = nitronylnitroxide). These complexes are ground-state analogs of the charge-separated excited states formed in photoinduced electron transfer reactions. The intraligand magnetic exchange interaction (J) in these complexes is mediated by the bridges and has been found to stabilize the triplet ground states of 1 and 2. Detailed spectroscopic and bonding calculations have been used to elucidate the role of the bridge fragment (B) and its conformation relative to donor (SQ) and acceptor (NN) on spin density distributions. The computed results correlate well with experimental nitrogen hyperfine coupling constants.