[Thesis]. Manchester, UK: The University of Manchester; 2016.
A range of small molecules of interest for use in organic semiconductor devices were
studied computationally. Trends in geometry, absorption spectra, molecular orbitals,
electrostatic potentials, reorganisation energies were studied. Results suggest that,
as with acenes, the performance of non-linear cata-condensed polyaromatic hydrocarbons
improves as number of fused benzene rings increases. The torsion in these molecules
did not appear to have a large impact on the conjugation across the core and little
effect on the absorption spectra, although it did affect the reorganisation energies
on which charge mobilities depend. Computational studies of mobilities of anthradithiophene
molecules were broadly able to reproduce trends seen experimentally and emphasised
the importance of crystal morphology. Experimental work was also carried out to search
for cocrystals between anthradithiophene derivatives. Many examples were found with
some mixtures forming different cocrystals at different mixture ratios. These results
were rationalised by a computational study that showed molecules which had a similar
binding energy were more likely to be able to form cocrystals. Cocrystal devices were
fabricated and 3 out of 7 showed a larger mobility than devices made out of its constituent
materials alone. The best of these had a mobility 65% higher than a device made out
of the constituent material with the largest mobility.An energy decomposition analysis
was carried out on a novel thallophilic system, a complex of thallium with a neutral
β-triketimine ligand which was found to form dimers with close Tl-Tl interactions.
Calculations show the electrostatic interaction to be repulsive for the dimer with
no counter ions, but attractive when 3,5-bistrifluoromethylphenyl borate counter ions
are included. This suggests the metallophilic interaction is counter ion-mediated,
requiring the anions to provide favourable electrostatics, even in the case of spatially
diffuse and distant counter ions such used here.To enable the studies described here
software was written for simulating absorption spectra. An implementation into the
Gaussian Suite of programs of an energy decomposition scheme and its extension to
include an empirical dispersion correction was also carried out.The work carried out
here has been published in two papers:(1) An orthogonal C–H borylation – cross-coupling
strategy for the preparation of tetrasubstituted ``A₂B₂''-chrysene derivatives with
tuneable photophysical properties, K. W. J. Heard, J. J Morrison, L. Weston, C. H.
Lo, L. Pirvu, J. Raftery, M. S. Little, J. J. W. McDouall, S. G. Yeates and P. Quayle,
Chem. Commun., 2015, 51, 6115.(2) Thallophilic Tl(I)–Tl(I) contacts mediated by Tl-aryl
interactions. A computational study, L. Weston, B. T. Pownall, F. S. Mair and J. J.
W. McDouall, Dalton Trans., 2016, 45, 8433.