DESIGN OF DONOR OLIGOMERS TO PRODUCE PARALLEL SPINS UPON ELECTRON-TRANSFER

Donor oligomers that give parallel spins upon electron transfer (ET) are designed. Tetrathiafurvalenes (TTFs) or tetraselenafulvalenes (TSFs) are linked with bonds > C=Y (Y = CH2, O, S, C(CN)(2)) that yield dynamic spin polarization (DSP) in favor of parallel spins between cation radicals of adjacent donors. Donors in these oligomers are not linked by planar because of steric hindrance. Planar oligomers are designed by adding a -S- bridge in the linkage of two donors. Oligomers linked with a metaphenylene group are also examined. pi electronic structures are calculated by the Pariser-Parr-Pople (PPP) model in the unrestricted Hartree-Fock (UHF) approximation using the Mataga-Nishimoto (M-N) or Ohno potential. Dications of all the dimers have the triplet UHF ground state. The DSPs, and consequently the singlet-triplet energy gaps (S-T gaps), are much larger in the M-N potential than the Ohno one. The S-T gaps are much larger in the planar dimers than in the nonplanar ones. Cation radicals of trimers and tetramers have quartet and quintet UHF ground states, respectively. Donor abilities and orbital energy gaps of oligomers and their cation radicals are studied.