EFFECT OF THE DIRECTIONALITY OF THE ESTER GROUP ON THE FORMATION OF HAIRPINS IN POLYESTERS CONTAINING NAPHTHALENE AND A FLEXIBLE SPACER

Steady-state fluorescence measurements and molecular dynamics simulati ons have been used to study the intramolecular formation of excimers i n five model compounds for polyesters containing naphthalene groups se parated by flexible spacers. The model compounds are derived from 2-hy droxynaphthalene and HOOC-(CH2)(n) -COOH, n = 2-6. The ratio of the in tensity of excimer and monomer emissions, I-D/I-M, is nearly independe nt of the viscosity of the medium, eta, over the range covered in dilu te solution. Although I-D/I-M is always very small, it shows an odd-ev en effect for the first four members of the series, with maxima when n is odd. Molecular dynamics simulations provide an explanation for the small values of I-D/I-M,their weak dependence on eta, and the trend o f I-D/I-M With n. The results for the present series of model compound s are compared with previous work, which reported larger values of I-D /I-M, and a stronger dependence of I-D/I-M on eta, for bichromophoric compounds derived from 2-naphthoic acid and aliphatic glycols, where t he direction of the ester groups is reversed. The origin of the differ ence in the behavior of I-D/l(M) in the two series is identified. (C) 1997 John Wiley & Sons, Inc.