To further investigate the UV–vis spectra for POAP and POAP/TiO2 were obtained. UV- and are shown in Fig. 7 Clearly, the prepared POAP/nanocrystalline TiO2 composites not only can strongly absorb the UV light but also can absorb the visible and near-IR light. The characteristic peaks of POAP appear at 225, 380 and 500 nm, which were attributed to π–π*, polaron-π*, and π-polaron transitions, respectively. This result shows that, in the presence of TiO2 nanoparticles, the UV absorption 380 nm is strengthened. Instead, there is suppression of a peak at 500 nm. It indicates that TiO2 nanoparticle has the effect on doping of conducting POAP. This shift shows shortening in the conjugation length that reported previously [22] or may be the coordinating complex formation between TiO2 and conducting polymer chains.