Synthesis and optical properties of polyethylenimine containing L-proline and optically active thymine derivatives

Preparation and optical properties of linear polyethylenimine (PEI) containing L -(?)-N-[(?)-2-(thymin-1-yl) propionyl] prolyl group as grafting pendant, [P-(?)Pro-(?)T], and its related monomer and dimer model compounds are described. Hypochromic effects and circular dichroism of these compounds were compared with those of PEI containing (?)-2-(thymin-1-yl) propionyl group as grafting pendant, [P-(?)T], which has no L -proline ring as a spacing group. P-(?)Pro-(?)T showed no exciton coupling of B_2u π-π^* transition although it showed large hypochromicity in neutral aqueous solution, implying that the stacking of the bases has no screw sense.