Structural organization of pi conjugated highly luminescent molecular material.

We report on striking evidence for a room temperature structural phase instability in p-hexaphenyl, inducing a nonplanar conformation of the molecules. Solid state proton NMR and single crystal x-ray diffraction allow the analysis of the organization, the individual dynamics and the involved symmetry breaking. The analysis of Raman spectra above and below room temperature reveals a singular behavior suggesting a modification of the overlap between the electronic wave function induced by the nonplanarity. These results provide a new basis to answer fundamental issues related to molecular and electronic materials and, in particular, luminescent organic devices.

Electrochemical impedance spectroscopy and electron spin resonance characterization of the conductive state of parasexiphenylene electrochemically intercalated with sodium.

The electrochemical intercalation of sodium ions into parasexiphenylene (PSP) was studied by electron spin resonance (ESR) and electrochemical impedance spectroscopy (EIS). These complementary techniques give informations about the conduction state of the host material as a function of the doping rate both in the intercalation and deintercalation processes. These data were compared to the previous works concerning the intercalation of alkaline ions into polyparaphenylene (PPP).

Raman spectroelectrochemical study of sodium intercalation into poly(p-phenylene).

The structural defects formed along the polymer chain during the electrochemical intercalation of sodium into polyparaphenylene (PPP) were investigated by in situ FT Raman measurements with an excitation wavelength of 1064 nm. Our Raman data are compared with those obtained for PPP and its oligomers intercalated with Na(+) ions by chemical ways. The coexistence of polarons and bipolarons is observed in the early stages of the intercalation process. When the doping level increases polarons are transformed to bipolarons, then in the highly intercalated sample (corresponding to a composition close to Na(0.5)(C(6)H(4))), bipolarons are the main structural defects. This evolution, which is reversible, is in accordance with the electron spin resonance (ESR) data of PPP intercalated with sodium ions in the same experimental conditions.