Pressure Effect to the Molecular Structure of Ladder-type Poly(Para-phenylene) Revealed by Raman Spectroscopy

ABSTRACT Raman scattering spectra of blue light-emitted organic conjugated polymer, ladder-type poly para-phenylene with a phenyl ring in the side chain (Ph-LPPP), in the form of powder with trace-concentrations of metallic impurities under various pressures are measured. We find that Raman spectra shift to higher frequency with the increase of pressure, indicating a strong electron-phonon interaction. We also find that the shift rates of Raman peaks from the backbone of Ph-LPPP are different comparing to our early observations of Raman spectra of methyl substituted ladder-type poly (Me-LPPP). Planarization under pressure, therefore, electronic delocalization is observed, which is also discovered from the optical properties of Ph-LPPP.