Thatti, Ravtej Singh (2016) The synthesis and properties of phenyl-cored thiophene dendrimers. (PhD thesis), Kingston University, .
Abstract
Dendrimers are globular macromolecules that have a range of applications. These nonnally exploit the individual prope1ties of the functional groups that make up the overall dendrimer. The polyvalent properties of dendrimers are widely used in biomedical scaffolds and catalysis. The internal cavities with the structure can also be harnessed for encapsulation. This application has evoked interest especially within the bio-medical field, using dendrimers as host molecules to increase the solubility of drug molecules. In this research, a set of dendrimers were prepared to test the potential of encapsulation and manipulation of the host structure. The dendrimer products contained thiophene spacer groups and a thiophene outer shell, with alkylated terminal groups. The hetcro aromatic rings were held around a phenyl core and internal generations to create the cavity space. After the phenyl-cored thiophene dendrimers were fully characterised, iodoform was used as a guest molecule and incorporated into the dendrimer structure to fonn an encapsulation complex. At this point it was seen that the second dendrimer had the potential to encapsulate and hold iodoform within its internal structure. UV-visible spectroscopy was used to verify how the presence and the overall amount of encapsulated iodofonn. Following these results a microgravimetric study was carried out, and it confinned the ratio of dendrimer to iodof01m (I :2.76). A minimised (MM3) molecular model of each of the dendrimers indicated that there was a possible van der Waals interaction between the thiophene moieties of the dendrimer and iodoform and confirmed that the second dendrimer was more likely to be efficient in encapsulating the guest molecule. Fmther molecular modelling showed that a four branched dendron was likely to increase the encapsulation potential. The dendrimers were exposed to iodine vapour to study the effect of doping. This was followed by UV-visible spectrometry, but data were mainly collected and compared by electrical conductivity measurements. It was shown that the dendrimer which contained a larger number of conjugated thiophene rings was much more conductive. The calculated charge carrier mobilities and conductivities were relatively low compared to those of large thiophene oligomers or polythiophene. This was expected as the charge had to hop frequently between dendrimer molecules compared to a single polymer. It was predicted that after encapsulation, the oxidised dendrimer complex would be affected by some torsion of the bond between the thiophene rings. Cyclic voltammetry for the second dendrimer displayed peaks for both n- and p-type doping. From this, the electrochemical band gap was calculated and compared to the optical band gap obtained from the UV-visible spectrum. The values were 2.6 ±0.1 eV.
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