Thesis (PhD)--Stellenbosch University, 2011. / ENGLISH ABSTRACT: The generation of ultrafast light pulses and the development of time resolved
spectroscopic techniques, such as the femtosecond pump probe spectroscopy
technique, have facilitated the study of ultrafast energy transfer in the photosynthetic
systems of green plants and photodynamic therapy drugs. It has
allowed the investigation of biological and chemical processes that take place on
the ultrafast timescale and has allowed us to obtain spectral and kinetic information
on energy transfer. In addition, it has allowed time resolved experiments
in which the transient absorption of species under investigation was observed
and has elucidated molecular dynamics. In the present work this was done with
a temporal resolution of approximately 200 fs and covering a pump-to-probe
delay range of 300 fs to 2 ns.
The main aims of this study were to characterise the femtosecond pump probe
spectroscopy system, to investigate the energy transfer in the natural light
harvesting complex II (LHC II) in view of future expansion to the study of
synthesized arti cial functional light harvesting complexes and nally to study
ultrafast processes in zinc phthalocyanine (ZnPc) systems.
In photosynthetic organisms, LHC II is the most abundant light harvesting
complex and it plays an important role in light harvesting and photoprotection.
The light energy is absorbed by light harvesting complexes and transferred to
a reaction centre (RC) in an ultrafast timescale.
Phthalocyanines are a new class of photosensitiser used for photodynamic
therapy. These drugs are used to treat small and super cial tumours. The
energy transfer from the singlet excited state to the triplet excited state occurs
on an ultrafast timescale. However, recent work done on zinc phthalocyanine has
proved that the determination of the ultrafast component remains a challenge.
Several ultrafast studies carried out on ZnPc in solvents have been not only
unsuccessful to give a clear picture of the ultrafast dynamics but have also
produced divergent results.
In this study, a characterisation of the femtosecond pump probe spectroscopy
setup was done. The samples under investigation were probed by a white light
continuum. The generation of the white light continuum introduced chirp,
which in uenced the temporal evolution of the transient absorption results.
The technique used to correct the chirp introduced by white light generation
is discussed in detail. Our femtosecond pump probe spectroscopy setup was
benchmarked by using a well known dye, namely malachite green. In addition,
the investigation of the transient absorption change of LHC II, an active component
in photosynthesis, as extracted from spinach leaves and the ultrafast
dynamics of a promising photosensitiser ZnPc in dimethyl sulfoxide (DMSO) as well as in dimethyl formamide (DMF) was done. The spectral and dynamic results
obtained using these three samples are described and exponential ts to the
absorbance decay curves used to estimate the timescales of the energy transfer
processes are presented. In this experiment, the dynamics and measured time
constants related to the energy transfer between the different types of chlorophyll
in LHC II was monitored, whereas with ZnPc, the dynamics and the
measured time constants associated with solvation dynamics and vibrational
relaxation was examined. / AFRIKAANSE OPSOMMING: Die vorming van ultravinnige lig pulse en die ontwikkeling van tyd opgelosde
spektroskopiese tegnieke, soos die femtosekonde pomp proef spektroskopie tegniek,
het die studie van ultravinnige energie oordrag in fotosintetiese stelsels van
groen plante en chemiese prosesse gefasiliteer, wat kan plaasvind op die ultravinnige
tyd skaal en laat dit toe om spektrale en kinetiese informasie oor die energie
oordrag te kan bepaal. Dit het ook dit moontlik gemaak om tyd opgelosde
eksperimente te kan doen waarin ons veranderlike absorbsie van die monster kon
ondersoek en die molekulere dinamika kon ontrafel. In hierdie werk is dit gedoen
met n tyd resolusie van omtrent 200 fs termyl 'n pomp-tot-proef tydvertraging
van 300 fs tot 2 ns gebruik is.
Die hoof doelwitte van hierdie werk was om 'n femtosekonde pomp proef
spektroskopie stelsel te karakteriseer, die energie oordrag in die natuurlike ligoes
kompleks II te ondersoek met die toekomstige uitbreiding van die studie na
sintetiese lig-oes komplekse as oogmerk en laastens om ultravinnige prosesse in
Sink Ftalosianiene stelsels te ondersoek.
In fotosintetiese organismes, is lig oes kompleks II die mees volop lig oes
kompleks en speel 'n belangrike rol in lig oes en foto skerming. Die lig energie
word geabsorbeer deur lig oes komplekse en dan oorgedra na reaksie middelpunte
in 'n ultravinnige tydskaal.
Ftalosianiene is 'n nuwe klas fotosensiteerder wat gebruik word in fotodinamiese
terapie. Hierdie dwelms word gebruik om klein en oppervlakkige
gewasse te behandel. Die energie oordrag van die opgewekte singlet tot die
triplet toestand vind plaas op die ultravinnige tydskaal. Onlangse navorsingswerke
het getoon dat die bepaling van die ultravinnige komponent 'n uitdaging
bly. Verskeie vorige ondersoeke is gedoen op Sink Ftalosianiene in verskeie
oplosmiddels, en nie net het hierdie studies nie 'n helder prentjie verskaf van die
ultravinnige dinamika nie, maar het ook divergerende resultate opgelewer.
In hierdie werk word 'n karakterisering van die femtosekonde pomp proef
spektroskopie stelsel gedoen. Die monsters is ondersoek met 'n wit lig kontinuum
proef. Die vorming van die wit lig kontinuum het tjirp veroorsaak, wat
die tyd evolusie van die veranderlike absorbsie resultate beinvloed het. Die tegniek
wat gebruik was om die tjirp te korregeer word bespreek. Ons femtosekonde
pomp proef spektroskopie stelsel is gestandardiseer deur die welbekende kleurstof
malachiet groen. Ons het ook die veranderlike absorbsie van lig oes kompleks II
ondersoek, 'n aktiewe komponent in fotosintese, soos dit onttrek is uit spinasie
blare, asook die ultravinnige dinamika van die belowende photosensitizer Sink
Ftalosianiene in DMSO asook DMF. Die spektrale en dinamiese resultate verkry
vanaf hierdie drie monsters word beskryf en eksponensiele passings aan die absorbsie verval kurwes is gebruik om die tydskale van die energie oordrag prosesse
te skat. In hierdie eksperiment is dinamika en gemete tydkonstantes waargeneem
wat toegeskryf kan word aan die energie oordrag tussen verskillende
soorte chloro l in lig oes kompleks II. In die Sink Ftalosianien eksperimente is
dinamika en gemete tydkonstantes waargeneem wat toegeskryf kan word aan
solverings dinamika asook vibrasionele ontspanning.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:sun/oai:scholar.sun.ac.za:10019.1/17894 |
| Date | 12 1900 |
| Creators | Ombinda-Lemboumba, Saturnin |
| Contributors | Du Plessis, Anton, Steenkamp, Christine M., 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 | 99 p. : ill. |
| Rights | Stellenbosch University |
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