Circular dichroism of polyethylenimine containing optically active thymine derivatives as grafted pendants

Optical properties of linear polyethylenimine containing optically active (+)‐ or (−)‐2‐(thymin‐1‐yl)propionyl group as grafted pendant were investigated by circular dichroism (CD) and compared with those of the related monomer and dimer model compounds. CD spectra of the polymer in neutral aqueous solution were different from those of related model compounds, which suggest that the polymer exists in some ordered conformation (at least locally) to allow exciton coupling of π–π* (B2u) transition in the base chromophores along the polymer chain. This ordered conformation tends to be randomized on heating. The effects of complementary base pairing on the CD spectra have also been studied by using a linear polyethylenimine containing (±)‐2‐(adenin‐9‐yl) propionyl grafts and its related monomer and dimer models.