Surface structure of poly(3-alkylthiophene) films studied by atomic force microscopy

Tapping mode atomic force microscopy (AFM) was employed to study the surface structure of spin-coated and solvent-cast films of the newly synthesized electroluminescent copolymer TT9 and its fractions A and B. Fraction A is well soluble in chloroform while fraction B forms aggregates of high molecular weight in the same solvent. TT9 and fraction A are photoluminescent; fraction B is not. TT9 spin-coated and solvent-cast films show similar morphologies characterized by wormlike structures. Solvent-cast films formed by fraction A have a large density of defects. Fraction B forms larger structures, giving rise to more corrugated surfaces. These structures are formed by grains of rather uniform size, likely to be related to the aggregates already present in solution. For all the examined films, the surface roughness scales in the same way with the linear dimension of the surface, suggesting similar growth mechanisms

Use of Size Exclusion Chromatography to study the protective effect of radical scavengers on oxygen free radical-induced degradation of hyaluronic acid

A size exclusion chromatography (SEC) method has been established for the study of hyaluronic acid depolymerization induced by oxygen free radicals and of the protective effect of two widely employed anti-inflammatory agents, piroxicam and tenoxicam. Molecular weight distribution of hyaluronic acid was determined by aqueous SEC equipped with absolute online detectors, light scattering detector and a viscometer. Ten min exposure of the macromolecules to a flux of hydroxyl radicals generated by xanthine/xanthine oxidase/Fe 2+ system caused massive depolymerization (Mw fell from 4.7 \ub7 105 to 8.7 \ub7 104). Both drugs exhibited a dose-dependent protective effect on hyaluronic acid degradation due to their radical scavenging properties. Tenoxicam was far more active than piroxicam in quenching highly reactive hydroxyl radicals (minimal effective concentrations 25 vs. 250 \u3bcM). This method gives a more complete analytical profile of the macromolecules with respect to conventional techniques

Efficient crystallization induced emissive materials based on a simple push-pull molecular structure

Solid state luminescent materials are the subject of ever growing interest both from a scientific and a technological point of view. Aggregation caused quenching (ACQ) processes however represent an obstacle to the development of most luminogens in the condensed phase. This is why particularly fascinating are those materials showing higher emission intensity in the solid state than in solution. Here we report on three 4-dialkylamino-2-benzylidene malonic acid dialkyl esters, very simple push-pull molecules, which are hardly emissive in solution and in the amorphous phase but become good emitters in the crystalline phase according to what has been indicated as crystallization induced emission (CIE). Thanks to combined emission and NMR spectroscopies at different temperatures on the prototype compound 4-dimethylamino-2-benzylidene malonic acid dimethyl ester in solution, we give full evidence that a restricted intramolecular rotation (RIR) phenomenon, in particular the hindered rotation around the aryl main axis of the compound, is at the origin of this behaviour. In addition, solid state photophysical and X-ray diffraction structural characterization allow us to identify J-dimeric interactions as responsible for the particularly intense emission of two of the three compounds. Moreover, by exploiting the compounds' acidochromic properties, applications in sensors and optoelectronics are envisaged

High photoluminescence efficiency in substituted polythiophene aggregates

In this paper we discuss the optical (absorption and photoluminescence) and solvatochromic properties of a newly synthesized alternating copolymer based on poly(3-alkylthiophene) structure. In this copolymer an unsubstituted thiophene ring is linked to a 3-alkyl-substituted thiophene, the two repeating units being alternated in the copolymer chains. Moreover, a bulky group, THP, with high steric hindrance has been introduced in the side chain. This copolymer, designed to preserve the backbone planarity of polythiophenes and to prevent a close packing arrangement through the non-regioregular insertion of the bulky substituted monomer, shows high PL quantum yield in the solid state and in solution aggregates. The electroluminescence of this copolymer is reported for a simple single layer device