Novel Oligoradicals and High Spin Formation

Abstract

Abstract Orthogonal alignment and variation of the MO-coefficients at the bridgehead postion has been tested for high spin formation in directly linked arylenes. In 2,21-bipyrenyl and para-terpyrenyl possessing very small MO-coefficients but also small steric indrance bi- and triradicalanionss are found to be in low spin groundstate, with thermally excited triplet and quartet states 100-1000 calmol−1 higher in energy, respectively. For 9,91-bianthryl biradical formation is well established, such that higher oligomers have been charged resulting in a S = 3/2 for the trimer, a S = 2 for the tetramer and a polyanionradical with descrete S = 1, S = 3/2, and S = 2 states in the polymer, where this highly charged material becomes insoluble. The ground state is again low spin due to increased deviation from orthogonality at low temperatures. The thermally activated higher spin multiplicities are found with AEST= 60 cal/mol (S=1), AEDQua = 120 Cal/mol (S=3/2), and AESQuin = 180 cal/mol (s=2). In another approach ...