Energy Transfer Dynamics in a Series of Conjugated Polyelectrolytes with Varying Chain Length

A time-resolved and steady state photophysical study of a family of conjugated polyelectrolytes (CPEs) with variable chain lengths (ranging from 8 to 108 polymer repeat units per chain) is reported. The CPEs investigated are poly(phenylene ethynelene)s substituted with two carboxylate groups per polymer repeat unit to provide water and methanol soluble conjugated polyelectrolytes. Steady state and ultrafast time-resolved fluorescence and anisotropy measurements were performed to explore the role of chain lengths on the energy transfer processes. We find that the CPEs aggregate under almost all conditions, with the degree of aggregation depending on the length of the conjugated polyelectrolyte chains. These CPEs are highly rigid and planar and present a very small loss of anisotropy during their emission lifetime.