RESUMO
Polarons exist when charges are injected into organic semiconductors due to their strong coupling with the lattice phonons, significantly affecting electronic charge-transport properties. Understanding the formation and (de)localization of polarons is therefore critical for further developing organic semiconductors as a future electronics platform. However, there are very few studies reported in this area. In particular, there is no direct in situ monitoring of polaron formation and identification of its dependence on molecular structure and impact on electrical properties, limiting further advancement in organic electronics. Herein, how a minor modification of side-chain density in thiophene-based conjugated polymers affects the polaron formation via electrochemical doping, changing the polymers' electrical response to the surrounding dielectric environment for gas sensing, is demonstrated. It is found that the reduction in side-chain density results in a multistep polaron formation, leading to an initial formation of localized polarons in thiophene units without side chains. Reduced side-chain density also allows the formation of a high density of polarons with fewer polymer structural changes. More numerous but more localized polarons generate a stronger analyte response but without the selectivity between polar and non-polar solvents, which is different from the more delocalized polarons that show clear selectivity. The results provide important molecular understanding and design rules for the polaron formation and its impact on electrical properties.
RESUMO
AIMS AND BACKGROUND: Biological variables linked to genomic instability were examined and related to survival in 52 patients affected by ovarian carcinoma and nine patients with low malignant potential tumors (LMP). METHODS: DNA ploidy was measured by image cytometry in isolated neoplastic cells; the mitotic index was measured in Feulgen-toluidine blue-stained sections and p53 was investigated by immunohistochemistry. RESULTS: Twenty-five tumors (4 LMP) were peridiploid (ploidy < 2.25c), 22 tumors (4 LMP) were hyperdiploid (2.25c > ploidy < 2.9c) and 14 (1 LMP) had high ploidy (> or = 2.9c). MI ranged from 0.3 to 24.2 with a mean of 1.8 for LMP and 6.8 for carcinomas (P<0.001). Widespread p53 overexpression was detected in 49% of carcinomas and in none of the LMP tumors. CONCLUSIONS: Survival analysis performed in patients with carcinomas indicated that, of the examined biological variables, only MI was moderately associated with survival in a subgroup of early-stage patients.
