Infrared photoexcitation spectra of conducting polymer/methanofullerene films

We report photoinduced absorption (PIA) and photoinduced reflectance (PIR) spectra of poly(3-octyl thiophene)-methanofullerene films. As a result of the efficient photoinduced intermolecular charge transfer, the PIA and PIR spectra of the composite films are significantly enhanced in magnitude over those in either of the component materials. From the PIA and PIR spectra, the corresponding changes in the complex refractive index, ΔN = Δn(ω)+iΔϰ(ω), are obtained. The results indicate that the PIA spectra are dominated by Δϰ(ω), while the PIR spectra are dominated mainly by Δn(ω). The implications of these photoinduced changes in the index resulting from photoexcitations are discussed in terms of potential optoelectronic and nonlinear optical applications of these materials.