Solution processing of oligothiophene molecules is shown to produce a range of particles with distinct morphologies. Once isolated on a substrate, the optical and electronic properties of individual particles were studied. From polarized scanning confocal microscopy experiments, distinct particles that are identifiable by shape were shown to have similar emission spectra except in regard to the 0-0 vibronic band intensity. This suppression of the 0-0 vibronic band correlates to the amount of energetic disorder present in a weakly coupled H-aggregate. The studied particles ranged from moderate to almost complete suppression of the 0-0 vibronic band when compared to the emission spectrum of the isolated molecule in solution. All particles were found to have a high degree of geometric order (molecular alignment) as observed from the fluorescence dichroism (FD) values of around 0.7-0.8 for all the studied morphologies. The structural and electronic properties of the particles were investigated with Kelvin probe force microscopy (KPFM) to measure the local contact potential (LCP) difference, a quantity that is closely related to the differences in intermolecular charge distribution between the oligothiophene particles. The LCP was found to vary by as much as 70 mV between different oligothiophene particles and a trend was observed that correlated the LCP changes with the amount of energetic disorder present, as signified by the suppression of the 0-0 vibronic peak in the emission spectra. Combined polarized scanning confocal microscopy studies, along with KPFM measurements, help to provide fundamental insights into the role of morphology, molecular packing, and intermolecular charge distributions in oligiothiophene particles.
Electropolymerization of bithiophene-substituted cadmium(II) Schiff base complexes forms thin conducting metallopolymer films with metal centers distributed throughout. The metal centers act as seed points for direct growth of CdS nanoparticles within the polymer matrix under mild reaction conditions. This synthetic approach offers control over both the size and distribution density of the nanoparticles formed within the polymer film. The resulting hybrid materials hold promise for a variety of organic electronic and optoelectronic applications.
For many emerging applications, nanocrystals are surface functionalized with polymers to
control self-assembly, prevent aggregation, and promote incorporation into polymer matrices
and biological systems. The hydrodynamic diameter of these nanoparticle–polymer
complexes is a critical factor for many applications, and predicting this size is
complicated by the fact that the structure of the grafted polymer at a nanocrystalline
interface is not generally established. In this work we evaluate using size-exclusion
chromatography the overall hydrodynamic diameter of nanocrystals (Au, CdSe,
d<5 nm) surface coated with polystyrene of varying molecular weight. The polymer is tethered
to the nanoparticles via a terminal thiol to provide strong attachment. Our data
show that at full coverage the polymer assumes a brush conformation and is
44% longer than the unbound polymer in solution. The brush conformation is
confirmed by comparison with models used to describe polymer brushes at flat
interfaces. From this work, we suggest an empirical formula which predicts the
hydrodynamic diameter of polymer coated nanoparticles based on the size of the
nanoparticle core and the size of the randomly coiled unbound polymer in solution.
Electropolymerization of novel gallium Schiff-base complexes results in conducting metallopolymers containing either coordinatively saturated or unsaturated gallium metal centers. Depending on the chemical coordination of the metal centers, the embedded metal ions can act as seed points for the direct growth of size-controlled gallium sulfide nanoparticles in a conducting polymer, yielding a hybrid electronic material.
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