Matching Items (3)
Description
A clean and sustainable alternative to fossil fuels is solar energy. For efficient use of solar energy to be realized, artificial systems that can effectively capture and convert sunlight into a usable form of energy have to be developed. In natural photosynthesis, antenna chlorophylls and carotenoids capture sunlight and transfer the resulting excitation energy to the photosynthetic reaction center (PRC). Small reorganization energy, λ and well-balanced electronic coupling between donors and acceptors in the PRC favor formation of a highly efficient charge-separated (CS) state. By covalently linking electron/energy donors to acceptors, organic molecular dyads and triads that mimic natural photosynthesis were synthesized and studied. Peripherally linked free base phthalocyanine (Pc)-fullerene (C60) and a zinc (Zn) phthalocyanine-C60 dyads were synthesized. Photoexcitation of the Pc moiety resulted in singlet-singlet energy transfer to the attached C60, followed by electron transfer. The lifetime of the CS state was 94 ps. Linking C60 axially to silicon (Si) Pc, a lifetime of the CS state of 4.5 ns was realized. The exceptionally long-lived CS state of the SiPc-C60 dyad qualifies it for applications in solar energy conversion devices. A secondary electron donor was linked to the dyad to obtain a carotenoid (Car)-SiPc-C60 triad and ferrocene (Fc)-SiPc-C60 triad. Excitation of the SiPc moiety resulted in fast electron transfer from the Car or Fc secondary electron donors to the C60. The lifetime of the CS state was 17 ps and 1.2 ps in Car-SiPc-C60 and Fc-SiPc-C60, respectively. In Chapter 3, an efficient synthetic route that yielded regioselective oxidative porphyrin dimerization is presented. Using Cu2+ as the oxidant, meso-β doubly-connected fused porphyrin dimers were obtained in very high yields. Removal of the copper from the macrocycle affords a free base porphyrin dimer. This allows for exchange of metals and provides a route to a wider range of metallporphyrin dimers. In Chapter 4, the development of an efficient and an expedient route to bacteriopurpurin synthesis is discussed. Meso-10,20- diformylation of porphyrin was achieved and one-pot porphyrin diacrylate synthesis and cyclization to afford bacteriopurpurin was realized. The bacteriopurpurin had a reduction potential of - 0.85 V vs SCE and λmax, 845 nm.
ContributorsArero, Jaro (Author) / Gust, Devens (Thesis advisor) / Moore, Ana (Committee member) / Gould, Ian (Committee member) / Arizona State University (Publisher)
Created2014
Description
Wide spread adoption of photovoltaic technology is limited by cost. Developing photovoltaics based on low-cost materials and processing techniques is one strategy for reducing the cost of electricity generated by photovoltaics. With this in mind, novel porphyrin and porphyrin-fullerene electropolymers have been developed here at Arizona State University. Porphyrins are attractive for inclusion in the light absorbing layer of photovoltaics due to their high absorption coefficients (on the order of 105 cm-1) and porphyrin-fullerene dyads are attractive for use in photovoltaics due to their ability to produce ultrafast photoinduced charge separation (on the order of 10-15 s). The focus of this thesis is the characterization of the photovoltaic properties of these electropolymer films. Films formed on transparent conductive oxide (TCO) substrates were contacted using a mercury drop electrode in order to measure photocurrent spectra and current-voltage curves. Surface treatment of both the TCO substrate and the mercury drop is shown to have a dramatic effect on the photovoltaic performance of the electropolymer films. Treating the TCO substrates with chlorotrimethylsilane and the mercury drop with hexanethiol was found to produce an optimal tradeoff between photocurrent and photovoltage. Incident photon to current efficiency spectra of the films show that the dominant photocurrent generation mechanism in this system is located at the polymer-mercury interface. The optical field intensity at this interface approaches zero due to interference from the light reflected by the mercury surface. Reliance upon photocurrent generation at this interface limits the performance of this system and suggests that these polymers may be useful in solar cells which have structures optimized to take advantage of their internal optical field distributions.
ContributorsBridgewater, James W (Author) / Gust, Devens (Thesis advisor) / Tao, Nongjian (Thesis advisor) / Gould, Ian (Committee member) / Diaz, Rodolfo (Committee member) / Arizona State University (Publisher)
Created2014
Description
As sunlight is an ideal source of energy on a global scale, there are several approaches being developed to harvest it and convert it to a form that can be used. One of these is though mimicking the processes in natural photosynthesis. Artificial photosynthetic systems include dye sensitized solar cells for the conversion of sunlight to electricity, and photoelectrosynthetic cells which use sunlight to drive water oxidation and hydrogen production to convert sunlight to energy stored in fuel. Both of these approaches include the process of the conversion of light energy into chemical potential in the form of a charge-separated state via molecular compounds. Porphyrins are commonly used as sensitizers as they have well suited properties for these applications. A high potential porphyrin with four nitrile groups at the beta positions, a β-cyanoporphyrin (CyP), was investigated and found to be an excellent electron acceptor, as well as have the necessary properties to be used as a sensitizer for photoelectrosynthetic cells for water oxidation. A new synthetic method was developed which allowed for the CyP to be used in a number of studies in artificial photosynthetic systems. This dissertation reports the theories behind, and the results of four studies utilizing a CyP for the first time; as a sensitizer in a DSSC for an investigation of its use in light driven water oxidation photoelectrosynthetic cells, as an electron acceptor in a proton coupled electron transfer system, in a carotene-CyP dyad to study energy and electron transfer processes between these moieties, and in a molecular triad to study a unique electron transfer process from a C60 radical anion to the CyP. It has been found that CyPs can be used as powerful electron acceptors in molecular systems to provide a large driving force for electron transfer that can aid in the process of the conversion of light to electrochemical potential. The results from these studies have led to a better understanding of the properties of CyPs, and have provided new insight into several electron transfer reactions.
ContributorsAntoniuk-Pablant, Antaeres' Dawn (Author) / Gust, Devens (Thesis advisor) / Moore, Ana L (Committee member) / Ghirlanda, Giovanna (Committee member) / Arizona State University (Publisher)
Created2015