Novel Photo-excited Triplet State Arising from Four Unpaired Electrons: (pi)-Topology and Spin Alignment in Excited State of Organic Spin System

A novel photo-excited state with the intermediate spin (S = 1) arising from four unpaired spins and a nearly degenerate quintet (S = 2) excited state were detected for 1, which was designed utilizing the photo-excited triplet spin coupler by taking (pi)-topology into account. The unique triplet state has an interesting electronic structure, which D value is reduced by the antiferromagnetic spin alignment between two radical spins through the excited spin coupler.