Thesis (MSc)--Stellenbosch University, 2012. / AFRIKAANSE OPSOMMING: Berekeninge met Density Functional Theory (DFT) is ’n nuttige tegniek om die dinamika
van molekules op potensiële energievlakke te verstaan. Beginnende met ’n
prototipe molekuul formaldimien, wat die kern vorm van die groter fotochromiese
molekuul dithizonatophenyl kwik (DPM), word die modellering van die molekuul
meer ingewikkeld tot laasgenoemde bestudeer kan word asook sy fotochromiese
afgeleides wat vervanging van elektronryk en elektronarm radikale by orto, meta en
para posisies van die phenyl ringe insluit. DFT berekeninge word met spektra van
Absorpsiespektroskopie met UV en sigbare lig asook tyd opgeloste spektra, verkry
dmv femtosekondespektroskopie, vergelyk. In pol^ere aprotiese, pol^ere protiese en
nie-pol^ere oplosmiddels, isomeriseer die molekuul om die C=N dubbelbinding. Daar
kan tussen die twee isomere onderskei word deur dat die een in oplossing in sy
grondtoestand blou en die ander een oranje voorkom. Die isomerisering is’n fotogeinduseerde
proses. Die optimering van die molekul^ere struktuur, absorpsiespektra,
oplosmiddel-afhanklikheid, en potensiële energievlak metings van die molekuul word
bestudeer. Die sterk/swak wisselwerking wat in pol^ere protiese/aprotiese oplosmiddels
verskyn word geopenbaar deur die hoe/lae absorpsie van die sekond^ere bande
van die molekules. Daar is gevind dat die absorpsiespektra van DPM bathochromies
in oplosmiddels met hoë diëlektriese konstantes is. Vir die potensiële energievlak
berekeninge van die grondtoestand word rigiede en ontspanne metodes gebruik waar
laasgenoemde met gebroke simmetrie berekeninge verkry word. Van alle metodes
wat vir berekeninge gebruik was, gee die B3LYP/CEP-31G metode die beste benadering
aan eksperimentele data. Alle berekeninge word gedoen met twee bekende
sagteware pakkette; Amsterdam Density Functional (ADF) en Gaussian, wat op twee
verskillende DFT metodes gebaseer is. / ENGLISH ABSTRACT: Density functional theory is a useful computational tool in the understanding of
molecular dynamics on potential energy surfaces. Starting with a prototype molecule
formaldimine, the photochromic molecule dithizonatophenylmercury II (DPM) and a
set of its photochromic derivatives, (involving substitutions of electron donating and
electron withdrawing substituents at ortho, meta and para positions of the dithizonato
phenyl rings), are studied through density functional calculation in comparison
with steady state absorption spectra obtained from UV-Visible and femto second
spectroscopy experiments. In polar aprotic, polar protic and non-polar solvents these
molecules isomerise around C=N double bond chromophore, from orange electronic
ground states to blue electronic ground states upon photo-excitation. We investigate
the structural optimisations, the absorption spectra, the solvent dependence and the
potential energy surface (PES) of these molecules. The strong (weak) interactions
exhibited by the polar protic (aprotic) solvents used are revealed through high (low)
absorbance in the secondary bands of these molecules. The absorption spectra of
DPM are found to be bathochromic in solvents with high dielectric constants. For
the ground state PES calculation we make use of rigid and relaxed methods, and the
latter is obtained through broken symmetry calculation. Of all the methods used in
calculation, B3LYP/CEP-31G method gives the best approximation to the experimental
data. All calculations are done using the two renown software, Amsterdam
Density Functional (ADF) and Gaussian, availing their different density functional
methods.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/20345 |
| Date | 03 1900 |
| Creators | Olaoye, Olufemi Opeyemi. |
| Contributors | Schwoerer, Heinrich P. H., Rohwer, Erich G., Stellenbosch University. Faculty of Science. Dept. of Physics. |
| Publisher | Stellenbosch : Stellenbosch University |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
| Format | 86 p. : ill. |
| Rights | Stellenbosch University |
Page generated in 0.0023 seconds