Dynamics of conformational transitions to isomeric states favoring intramolecular excimer formation in aromatic polyesters with methylene or oxyethylene spacers

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Abstract
The dynamic rotational isomeric state formalism described in the preceding paper is used to calculate the rate of first passage from non-excimer-forming conformations to excimer-forming conformations in seven aromatic polyesters with different flexible spacers between the aromatic rings. The excimer-forming conformations in these polymers were identified recently by Mendicuti et al. The time dependence of the probability that a flexible spacer will at least once have passed through an excimer-forming conformation can be written as the product of two factors, one of which is time dependent, the other of which is determined by the equilibrium conformational statistics. In the polyesters considered here, the static factor is much more sensitive than the dynamic factor to the identity of the flexible spacers. Consequently, the equilibrium chain statistics provides a good description of the relative excimer population for these polyesters, even at times where the dynamic contribution is significant. The chromophores in these polyesters have such short fluorescence lifetimes that it is only in the most mobile flexible segments that there is an important dynamic contribution to the excimer formation.

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