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- Creators: Gust, Devens
- Creators: Moore, Thomas
Description
The first chapter reviews three decades of artificial photosynthetic research conducted by the A. Moore, T. Moore, and D. Gust research group. Several carotenoid (Car) and tetrapyrrole containing molecules were synthesized and investigated for excitation energy transfer (EET), photoregulation, and photoprotective functions. These artificial photosynthetic compounds mimicked known processes and investigated proposed mechanisms in natural systems. This research leads to a greater understanding of photosynthesis and design concepts for organic based solar energy conversion devices. The second and third chapters analyze the triplet energy transfer in carotenoid containing dyads. Transient absorption, time-resolved FTIR and resonance Raman spectra revealed that in a 4-amide linked carotenophthalocyanine dyads the Car triplet state is shared across the larger conjugated system, which is similar to protein complexes in oxygenic photosynthetic organisms. In a carotenopurpurin dyad (CarPur) a methylene ester covalent bond prevents the purpurin (Pur) from influencing the Car triplet based on the transient absorption, time-resolved FTIR and resonance Raman spectra. Thus CarPur resembles the antenna proteins from anoxygenic photosynthetic bacteria. Additional examples of carotenoporphyrin dyads further demonstrates the need for orbital overlap for ultrafast triplet energy transfer and the formations of possible intramolecular charge transfer state. The fourth chapter studies a 4-amino phenyl carotenophthalocyanine and its model compounds using high temporal resolution transient absorption spectroscopy techniques. EET from the Car second excited (S2) state to the phthalocyanine (Pc) was determined to be 37% and a coupled hot ground state (S*)/Pc excited state spectrum was observed. Excitation of the tetrapyrrole portion of the dyad did not yield any kinetic differences, but there was an S* signal during the excited states of the dyad. This demonstrates the EET and photoregulating properties of this artificial photosynthetic compound are similar to those of natural photosynthesis. The last chapter covers the synthesis of silicon Pc (SiPc) dyes and the methods for attaching them to gold nanoparticles and flat gold surfaces. SiPc attached to patterned gold surfaces had unperturbed fluorescence, however the selectivity for the gold was low, so alternative materials are under investigation to improve the dye's selectivity for the gold surface.
ContributorsWongCarter, Katherine (Author) / Moore, Ana L (Thesis advisor) / Gust, Devens (Committee member) / Gould, Ian (Committee member) / Arizona State University (Publisher)
Created2014
Description
Natural photosynthesis features a complex biophysical/chemical process that requires sunlight to produce energy rich products. It is one of the most important processes responsible for the appearance and sustainability of life on earth. The first part of the thesis focuses on understanding the mechanisms involved in regulation of light harvesting, which is necessary to balance the absorption and utilization of light energy and in that way reduce the effect caused by photooxidative damage. In photosynthesis, carotenoids are responsible not only for collection of light, but also play a major role in protecting the photosynthetic system. To investigate the role of carotenoids in the quenching of the excited state of cyclic tetrapyrroles, two sets of dyads were studied. Both sets of dyads contain zinc phthalocyanine (Pc) covalently attached to carotenoids of varying conjugation lengths. In the first set of dyads, carotenoids were attached to the phthalocyanine via amide linkage. This set of dyads serves as a good model for understanding the molecular "gear-shift" mechanism, where the addition of one double bond can turn the carotenoid from a nonquencher to a very strong quencher of the excited state of a tetrapyrrole. In the second set of dyads, carotenoids were attached to phthalocyanine via a phenyl amino group. Two independent studies were performed on these dyads: femtosecond transient absorption and steady state fluorescence induced by two-photon excitation. In the transient absorption study it was observed that there is an instantaneous population of the carotenoid S1 state after Pc excitation, while two-photon excitation of the optically forbidden carotenoid S1 state shows 1Pc population. Both observations provide a strong indication of the existence of a shared excitonic state between carotenoid and Pc. Similar results were observed in LHC II complexes in plants, supporting the role of such interactions in photosynthetic down regulation. In the second chapter we describe the synthesis of porphyrin dyes functionalized with carboxylate and phosphonate anchoring groups to be used in the construction of photoelectrochemical cells containing a porphyrin-IrO2·nH2O complex immobilized on a TiO2 electrode. The research presented here is a step in the development of high potential porphyrin-metal oxide complexes to be used in the photooxidation of water. The last chapter focuses on developing synthetic strategies for the construction of an artificial antenna system consisting of porphyrin-silver nanoparticle conjugates, linked by DNA of varied length to study the distance dependence of the interaction between nanoparticles and the porphyrin chromophore. Preliminary studies indicate that at the distance of about 7-10 nm between porphyrin and silver nanoparticle is where the porphyrin absorption leading to fluorescence shows maximum enhancement. These new hybrid constructs will be helpful for designing efficient light harvesting systems.
ContributorsPillai, Smitha (Author) / Moore, Ana (Thesis advisor) / Moore, Thomas (Committee member) / Gould, Ian (Committee member) / Arizona State University (Publisher)
Created2011