The photophysics of pigments is influenced, to an extent depending on its structure, by the properties of the environment. Proteins represent a very specific environment at least in two aspects: i) they are native to most of the pigments in living systems; ii) they facilitate modifications of pigment configuration, leading to changes not only in its spectroscopic properties, but also in its functional abilities. In studies presented in this thesis, femtosecond pump-probe spectroscopy was used to study predominantly the photosynthetic antenna complexes of bacteria and algae. Based on spectroscopic evidence, the structural modifications of pigments imposed by the protein were deduced or hypothesized, together with their functional relevance.

The light harvesting systems of photosynthetic organisms harness solar energy by efficient light capture and subsequent transport of the light’s energy to a chemical reaction center. Man-made optical devices could benefit by mimicking these naturally occurring light harvesting processes. Supramolecular organic nanostructures, composed of the amphiphilic carbocyanine dye 3,3’-bis- (2-sulfopropyl)-5,5’,6,6’-tetrachloro-1,1’- dioctylbenzimida-carbocyanine (C8S3), self assemble in aqueous solution to form tubular, double-walled J-aggregates. These J-aggregates have drawn comparisons to light harvesting systems, owing to their optical and structural similarities to the cylindrical chlorosomes (antenna) from green sulfur bacteria. This research utilizes optical spectroscopy and microscopy to study the supramolecular origins of the exciton transitions and fundamental nature of exciton energy transport in C8S3 artificial light harvesting systems. Two J-aggregate morphologies are investigated: well-separated, double-walled nanotubes and bundles of agglomerated nanotubes. Linear dichroism spectroscopy of flow-aligned nanotubes is used to generate the first quantitative, polarized model for the complicated C8S3 nanotube excitonic absorption spectrum that is consistent with theoretical predictions. The C8S3 J-aggregate photophysical properties are further explored, as the Stokes shift, quantum yield, and spectral line broadening are measured as a function of temperature from 77 – 298 K. The temperature-dependent emission ratios of the C8S3 J-aggregate two-band fluorescence spectra reveal that nanotube emission is well described with Boltzmann partitioning between states, while the bundles’ is not. Finally, understanding energy transport in these materials is critical for the proposed use of artificial light harvesting systems in optoelectronic devices. The spatial extent of energy transfer in individual C8S3 J- aggregate structures is directly determined using fluorescence imaging. We find that aggregate structural hierarchy greatly influences exciton transport distances: impressive average exciton migration distances of ~ 150 nm are measured along the nanotubes, while these distances increase to over 500 nm in the bundle superstructures. / text

The emerging field of nanotechnology, which spans diverse areas such as nanoelectronics, medicine, chemical and pharmaceutical industries, biotechnology and computation, focuses on the development of devices whose improved performance is based on the utilization of self-assembled nanoscale components exhibiting unique properties owing to their miniaturized dimensions. The first phase in the conception of such multifunctional devices based on integrated technologies requires the study of basic principles behind the functional mechanism of nanoscale components, which could originate from individual nanoobjects or result as a collective behaviour of miniaturized unit structures. The comprehensive studies presented in this thesis encompass the mechanical, dynamical and photophysical aspects of three nanoscale systems. A newly developed europium sulfide nanocrystalline material is introduced. Advances in synthetic methods allowed for shape control of surface-functionalized EuS nanocrystals and the fabrication of multifunctional EuS-CdSe hybrid particles, whose unique structural and optical properties hold promise as useful attributes of integrated materials in developing technologies. A comprehensive study based on a new class of multifunctional nanomaterials, derived from the basic unit of barcoded metal nanorods is presented. Their chemical composition affords them the ability to undergo autonomous motion in the presence of a suitable fuel. The nature of their chemically powered self-propulsion locomotion was investigated, and plausible mechanisms for various motility modes were presented. Furthermore functionalization of striped metallic nanorods has been realized through the incorporation of chemically controlled flexible hinges displaying bendable properties. The structural aspect of the light harvesting machinery of a photosynthetic cryptophyte alga, Rhodomonas CS24, and the mobility of the antenna protein, PE545, in vivo were investigated. Information obtained through a combination of steady-state and time-resolved spectroscopy in conjunction with quantum chemical calculations aided in the elucidation of the dynamics and the mechanism of light harvesting in the multichromophoric phycobiliprotein phycocyanin PC645 in vitro. Investigation of the light-harvesting efficiency and optimization of energy transfer with respect to the structural organization of light-harvesting chromophores on the nanoscale, can provide us with fundamental information necessary for the development of synthetic light-harvesting devices capable of mimicking the efficiency of the natural system.

The studies presented in this thesis explore electronic energy transfer (EET) in light-harvesting antenna complexes and investigate the role of quantum coherence in EET. The dynamics of energy transfer are investigated in three distinct length scales and a different formulation of the exciton transport problem is applied at each scale. These scales include: the scale of a molecular dimer, the scale of a single protein and the scale of a molecular aggregate. The antenna protein phycoerythrin 545 (PE545) isolated from the photosynthetic cryptophyte algae Rhodomonas CS4 is specifically studied in two chapters of this thesis. It is found that formation of small aggregates delocalizes the excitation across chromophores of adjacent proteins, and that this delocalization has a dramatic effect in enhancing the rate of energy transfer between pigments. Furthermore, we investigate EET from a donor to an acceptor via an intermediate site and observe that interference of coherent pathways gives a finite correction to the transfer rate that is sensitively dependent on the nature of the vibrational interactions in the system. The statistical fluctuations of a system exhibiting EET are investigated in the final chapter. The techniques of non-equilibrium statistical mechanics are applied to investigate the steady-state of a typical system exhibiting EET that is perturbed out of equilibrium due to its interaction with a fluctuating bath.

The studies presented in this thesis explore electronic energy transfer (EET) in light-harvesting antenna complexes and investigate the role of quantum coherence in EET. The dynamics of energy transfer are investigated in three distinct length scales and a different formulation of the exciton transport problem is applied at each scale. These scales include: the scale of a molecular dimer, the scale of a single protein and the scale of a molecular aggregate. The antenna protein phycoerythrin 545 (PE545) isolated from the photosynthetic cryptophyte algae Rhodomonas CS4 is specifically studied in two chapters of this thesis. It is found that formation of small aggregates delocalizes the excitation across chromophores of adjacent proteins, and that this delocalization has a dramatic effect in enhancing the rate of energy transfer between pigments. Furthermore, we investigate EET from a donor to an acceptor via an intermediate site and observe that interference of coherent pathways gives a finite correction to the transfer rate that is sensitively dependent on the nature of the vibrational interactions in the system. The statistical fluctuations of a system exhibiting EET are investigated in the final chapter. The techniques of non-equilibrium statistical mechanics are applied to investigate the steady-state of a typical system exhibiting EET that is perturbed out of equilibrium due to its interaction with a fluctuating bath.

The emerging field of nanotechnology, which spans diverse areas such as nanoelectronics, medicine, chemical and pharmaceutical industries, biotechnology and computation, focuses on the development of devices whose improved performance is based on the utilization of self-assembled nanoscale components exhibiting unique properties owing to their miniaturized dimensions. The first phase in the conception of such multifunctional devices based on integrated technologies requires the study of basic principles behind the functional mechanism of nanoscale components, which could originate from individual nanoobjects or result as a collective behaviour of miniaturized unit structures. The comprehensive studies presented in this thesis encompass the mechanical, dynamical and photophysical aspects of three nanoscale systems. A newly developed europium sulfide nanocrystalline material is introduced. Advances in synthetic methods allowed for shape control of surface-functionalized EuS nanocrystals and the fabrication of multifunctional EuS-CdSe hybrid particles, whose unique structural and optical properties hold promise as useful attributes of integrated materials in developing technologies. A comprehensive study based on a new class of multifunctional nanomaterials, derived from the basic unit of barcoded metal nanorods is presented. Their chemical composition affords them the ability to undergo autonomous motion in the presence of a suitable fuel. The nature of their chemically powered self-propulsion locomotion was investigated, and plausible mechanisms for various motility modes were presented. Furthermore functionalization of striped metallic nanorods has been realized through the incorporation of chemically controlled flexible hinges displaying bendable properties. The structural aspect of the light harvesting machinery of a photosynthetic cryptophyte alga, Rhodomonas CS24, and the mobility of the antenna protein, PE545, in vivo were investigated. Information obtained through a combination of steady-state and time-resolved spectroscopy in conjunction with quantum chemical calculations aided in the elucidation of the dynamics and the mechanism of light harvesting in the multichromophoric phycobiliprotein phycocyanin PC645 in vitro. Investigation of the light-harvesting efficiency and optimization of energy transfer with respect to the structural organization of light-harvesting chromophores on the nanoscale, can provide us with fundamental information necessary for the development of synthetic light-harvesting devices capable of mimicking the efficiency of the natural system.

The global consumption of fossil fuels continues to increase due to the rapid growth of energy demand, as a consequence of expanding population and human activities. Fast climate change is another inescapable issue caused by humans that need to be addressed. The development of solar energy conversion technologies is widely considered as one of the most promising solutions to sustainably maintain a modern lifestyle of the society and create a carbon-neutral social development operation mode. The solar energy is carried and delivered in the form of electromagnetic fields. Therefore, the efficiency of photon collection is the primary factor to create any solar energy conversion systems. Through the inspiration from nature, the functionalized disorder, with a specific design and engineering, can introduce unusual light-matter interaction behaviors, and thus offer a potential capability to achieve perfect light harvesting. In my thesis, we develop complex Epsilon-Near-Zero (ENZ) metamaterials that can be used either as light capturing networks or the photoactive media by turning the energy damping ratio between radiative and non-radiative channels. We successfully integrate it into thin-film photovoltaic modules with showing an excellent performance enhancement led by broadband light localization effect. Thanks to universal of such complex ENZ metamaterials, with combining a thin layer of dielectric, we further develop efficient hot-carriers driven plasmonic photo-catalysts for artificial green chemical fuel synthesis. The detailed theoretic analysis is presented in this work.

Die pflanzliche Light-harvesting complex-Proteinfamilie besteht aus Proteinen mit vielfältigen Funktionen. Dabei ist die Funktion der Light-harvesting-like 3-Proteine (LIL3) sowie der One-helix-Proteine (OHPs) weitestgehend unbekannt. Im Rahmen dieser Arbeit wurde gezeigt, dass LIL3 nicht nur mit der Geranylgeranyl-Reduktase (CHLP), sondern auch mit der Protochlorophyllid-Oxidoreduktase (POR) interagiert. Sowohl CHLP als auch POR werden über die Interaktion zu LIL3 an die Thylakoidmembran gebunden und dadurch stabilisiert. Beide Enzyme liefern die direkten Vorstufen für den von der Chlorophyll-Synthase (CHLG) katalysierten finalen Chlorophyll-Syntheseschritt. Neben der Bestätigung der bereits früher gezeigten Chlorophyllbindung von LIL3 konnte eine Affinität zu den späten Intermediaten der Chlorophyllbiosynthese Proto IX, MgP, MgPMME und Pchlid nachgewiesen werden. Die größte Affinität bestand dabei gegenüber dem Substrat von POR, Pchlid. Basierend auf diesen Erkenntnissen wird LIL3 als Regulator der späten Chlorophyllbiosynthese-Schritte vorgeschlagen: LIL3 transportiert Substrate zwischen den Enzymen und ermöglicht durch die Bindung von CHLP und POR die Synthese der Chlorophyll-Edukte in räumlicher Nähe. Dadurch wird die Versorgung von CHLG mit dessen Edukten favorisiert. Beide OHP-Varianten (OHP1/2) bilden ausschließlich Heterodimere und binden Chlorophyll sowie Carotinoide im Verhältnis 3:1. Die Pigmentbindung basiert auf den konservierten Aminosäuren im Chlorophyllbindemotiv. An das OHP1-OHP2-Dimer bindet der PSII-Assemblierungsfaktor HCF244 und wird dadurch an der Membran verankert. HCF244 stabilisiert das OHP-Heterodimer und beide OHPs stabilisieren sich gegenseitig. Der heterotrimere OHP1-OHP2-HCF244-Komplex ist für die D1-Synthese wesentlich. Es wird vermutet, dass die OHPs an der co-translationalen Beladung von (p)D1 mit Pigmenten beteiligt sind sowie frühe Assemblierungsintermediate von PSII vor überschüssiger Anregungsenergie schützen. / The plant light-harvesting complex protein family comprises different members with a variety of functions. However, the function of the light-harvesting-like 3 proteins (LIL3) as well as the one-helix proteins (OHPs) is largely unknown. In this thesis, an interaction of LIL3 not only with geranylgeranyl-reductase (CHLP), but also with protochlorophyllide-oxidoreductase (POR) could be established. LIL3 tethers CHLP and POR to the thylakoid membrane, thereby conferring stability to both enzymes. Both CHLP and POR are synthesizing the direct chlorophyll precursors which are combined to chlorophyll by the subsequent chlorophyll synthase (CHLG). In addition to the chlorophyll binding ability of LIL3 reported earlier, an affinity of LIL3 towards the chlorophyll biosynthesis intermediates Proto IX, MgP, MgPMME, and Pchlide could be shown. Interestingly, the highest affinity of LIL3 was exerted towards Pchlide which is the substrate of POR. Therefore, LIL3 is postulated to shuffle the intermediates between enzymes and brings CHLP and POR in close proximity, which may help to supply CHLG with its substrates. Regarding the function of the OHPs an exclusive heterodimer formation of both the OHP1 and OHP2 variants could be shown. The OHP1-OHP2-heterodimer is able to bind chlorophyll and carotenoids in an approximate 3:1 ratio and pigment binding depends on dimer formation as well as the presence of the conserved amino acids in the chlorophyll binding motif. The PSII-assembly factor HCF244 is anchored to the thylakoid membrane by binding to both OHPs, thereby stabilizing the OHP-heterodimer. The heterotrimeric OHP1-OHP2-HCF244-complex is essential for D1 biosynthesis, although the exact molecular function of HCF244 is still unknown. It is suggested that the OHP-dimer is responsible for co-translational loading of (p)D1 with pigments as well as photoprotection of early PSII assembly intermediates.

Chlorins, as the core structures of chlorophylls, have been extensively studied for harvesting solar energy, fluorescent imaging and photodynamic therapy against cancer. This thesis is concerned with design and synthesis of novel chlorins as antennae for harvesting light and sensitising near infrared lanthanide luminescence. In the first part, a series of chlorin monomers, dimers and polymers were synthesised and their photophysical properties were characterised. The chlorin monomers were substituted with five-membered heterocycles, such as thiophenes and furans. These heterocycles function as auxochromes analogous to the natural ones in chlorophylls, and extend chlorin absorption and emission strongly to the red (up to λem = 680 nm). A borylation method was developed to prepare borylated chlorins, which gave access to directly linked chlorin dimers through Suzuki coupling reaction. Different regioisomers of chlorin dimer were prepared, including β-meso homodimers, meso-meso homodimers and heterodimers. The dimerisation resulted in red-shifted absorption and emission. Chlorin polymerisations were performed both electrochemically and chemically. Bis-thienylchlorins yielded chlorin films and an organic solvent soluble copolymer with hexylthiophene, respectively. These polymers from both polymerisations have red absorptions beyond 700 nm, and might be used as light-harvesting antennae. In the second part, chlorins were used as chromophores to sensitise near infrared lanthanide luminescence. Two types of chlorin-lanthanide dyads were prepared through lanthanide coordination with cyclen derivatives and dipicolinic acids (DPA). The cyclen-based dyads were poorly soluble in water, thus their near infrared emissions were not observed. The other type of complexes was fully soluble in H2O and THF. Both Nd and Yb emission were recorded even upon excitation into the Q bands of chlorins. In the dyads with free base chlorins, the singlet state of chlorins might be involved in the sensitisation of lanthanide luminescence. These DPA-based dyads presented two-color emission based on one chlorin and two-color excitation based on one lanthanide ion. These dyads would enable in theory 4-color imaging. In the last part, a microwave-assisted two-step synthesis was described to prepare dipyrromethanes, which are the key intermediates in the chlorin synthesis. This mild method took advantage of the nucleophilicity of pyrrole and the electrophilicity of N,N-dimethylaminomethyl pyrroles. The usually used acid catalysis is detrimental to many functionalities, thus our methods enable the synthesis of dipyrromethanes with acid sensitive groups or a formyl group.

Doctor of Philosophy / Department of Chemistry / Jun Li / Solar energy as a sustainable resource is a promising alternative to fossil fuels to solve the tremendous global energy crisis. Development of three generation of solar cells has promoted the best sunlight to electricity conversion efficiency above 40%. However, the most efficient solar cells rely on expensive nonsustainable raw materials in device fabrication. There is a trend to develop cost-effective biophotovoltaics that combines natural photosynthetic systems into artificial energy conversion devices such as dye sensitized solar cells (DSSCs). In this research, a model system employs natural extract light-harvesting complex II (LHCII) as a light-absorbing sensitizer to interface with semiconductive TiO₂ and plasmonic nanoparticles in DSSCs. The goal of this research is to understand the fundamental photon capture, energy transfer and charge separation processes of photosynthetic pigment-protein complexes along with improving biophotovoltaic performance based on this model system through tailoring engineering of TiO₂ nanostructures, attaching of the complexes, and incorporating plasmonic enhancement. The first study reports a novel approach to linking the spectroscopic properties of nanostructured LHCII with the photovoltaic performance of LHCII-sensitized solar cells (LSSCs). The aggregation allowed reorganization between individual trimers which dramatically increased the photocurrent, correlating well with the formation of charge-transfer (CT) states observed by absorption and fluorescence spectroscopy. The assembled solar cells demonstrated remarkable stability in both aqueous buffer and acetonitrile electrolytes over 30 days after LHCII being electrostatically immobilized on amine-functionalized TiO₂ surface. The motivation of the second study is to get insights into the plasmonic effects on the nature of energy/charge transfer processes at the interface of photosynthetic protein complexes and artificial photovoltaic materials. Three types of core-shell (metal@TiO₂) plasmonic nanoparticles (PNPs) were conjugated with LHCII trimers to form hybrid systems and incorporated into a DSSC platform built on a unique open three-dimensional (3D) photoanode consisting of TiO₂ nanotrees. Enhanced photon harvesting capability, more efficient energy transfer and charge separation at the LHCII/TiO₂ interface were confirmed in the LHCII-PNP hybrids, as revealed by spectroscopic and photovoltaic measurements, demonstrating that interfacing photosynthesis systems with specific artificial materials is a promising approach for high-performance biosolar cells. Furthermore, the final study reveals the mechanism of hot electron injection by employing a mesoporous core-shell (Au@TiO₂) network as a bridge material on a micro-gap electrode to conduct electricity under illumination and comparing the photoconductance to the photovolatic properties of the same material as photoanodes in DSSCs. Based on the correlation of the enhancements in photoconductance and photovoltaics, the contribution of hot electrons was deconvoluted from the plasmonic near-field effects.