Two different batches of substituted poly(p-phenylene-ethynylene)
[PPEs] were synthesized where the substituents dibutyl(a),
di-2-ethylhexyl(d) were placed on the 2,5 positions of the phenyl
rings. The PA spectrum of PPE(a) shows a polaron band at about
850cm-1. Whereas PPE(d) doesn't show any polaron absorption band.
Visible photomodulation spectrum of PPE(a) has two main bands at T=10K
around 1.25eV and 1.9eV plus a broad shoulder at 2.1eV. From PADMR
spectrum we found that in PPE(a), the 1.9eV PA has spin 1/2, thus it is
long-lived polaron generated in the polymer through photoexcitation,
whereas the 1.25eV PA doesn't have any spin 1/2 resonance.