Optical Spectroscopy of Grafted Poly(p-phenyleneethynylene)s in Water and Water−DMF Mixtures

The synthesis and spectral characterization of three grafted poly(p-phenyleneethynylene)s (PPE) are reported. These polymers contain identical chromophores/fluorophores yet show different absorption and emission spectra in DMF and DMF−water mixtures. While some of the spectral properties of the PPEs are similar to those of didodecyl-PPE, their spectroscopic properties in DMF−water mixtures differ significantly from those of didodecyl-PPE in CHCl3. An example is the lactide-substituted PPE, which shows absorption spectra that are reminiscent of those obtained for didodecyl-PPE in poor solvents but emission spectra that resemble those of didodecyl-PPE in a good solvent. Emission shifts occur in these PPEs when going from DMF to water. In the case of the lactide-PPE, a surprising hypsochromic emission shift of 10 nm is observed. This apparent shift is attributed to the preferred aggregation and self-quenching of the longer chains, leaving shorter, blue-emissive chains nonaggregated.