Highly controlled side-chain chromophore orientation in poly [N⁵-1-(1-pyrenyl)ethyl-L-glutamines]

Poly[N⁵-(R and S)-1-(1-pyrenyl)ethyl-L-glutamines] (1 and 2) were prepared by condensation of poly(L-glutamic acid) with optically resolved amines. In solution, these polymers, 2 in particular, gave large circular dichroism (CD) indicative of exciton coupling among the side-chain pyrene chromophores. When compared with the corresponding polymer with achiral side groups, i.e. poly(1-pyrenylmethyl-Lglutamine) (3), 1 and 2 not only gave much stronger CD, but also gave much reduced excimer emission with a significant hypsochromic shift of emission maximum. The highly controlled orientation of the side-chain chromophores is apparently brought about by the specific steric interactions among the bulky chiral side chains along the helical main chain.