4 research outputs found

    Photochemical investigation of porphyrins for use in Dye Sensitized Solar Cells

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    As Dye Sensitized Solar Cells (DSSCs) have become a more prominent focus of the research being published on alternative energy sources it is important to consider basic principles that show promise for improving the energy conversion efficiency of these cells. By choosing and building a dye system carefully it is possible to promote a process called triplet-triplet annihilation (TTA) which involves the upconversion of two relatively low energy triplet excited molecules to produce one highly excited singlet molecule and a ground state molecule (2 T1 Sn + S0 [n>1]). This process will give DSSCs the ability to take advantage of the photon-rich near infrared portion of the solar spectrum making them inherently more efficient than systems which cannot undergo TTA. Two dye systems which show promise as TTA capable light harvesters are zinc tetraphenylporphyrin (ZnTPP) and tin(IV)-dichloro,tetraphenylporphyrin (SnCl2TPP). The photophysical properties of ZnTPP are studied in its standard form as well as in its ligated form. Ligation of the central atom with nitrogen containing bidentate ligands (i.e. pyrazine, 4,4- bipyridine etc…) can have a profound effect on both the properties of the monomer as well as the aggregate behavior of solvated dyes and their interaction with each other. The properties of SnCl2TPP are also examined and in particular methods for the formation of stacked molecular columns as manipulation of interactions between the individual dyes can significantly impact their ability to undergo TTA. Spectral data indicate that ligation of the ZnTPP leads to the formation of a short lived charge transfer state which greatly decreases the lifetime of the S2 state while having little effect on the S1 decay kinetics. It also shows that there is little or no formation of six-coordinate ZnTPP (i.e. doubly ligated) which makes the formation of stacked supramolecular structures very difficult. Data concerning the electrochemical synthesis and chemical synthesis of a SnCl2TPP based stack were inconclusive but show some promise that may give direction to future work

    Electrochemical Studies of Capping Agent Adsorption Provide Insight into the Formation of Anisotropic Gold Nanocrystals

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    The ability of the 4-dimethylaminopyridine (DMAP) to stabilize and control the formation of anisotropic gold nanocrystals produced <i>via</i> the borohydride reduction of gold(III) salts is reported here. Electrochemical measurements of DMAP electrosorption on different low-index single crystal and polycrystalline electrodes is provided and shows a propensity for DMAP to preferentially adsorb on {100} facets. Measuring the electrochemical potential during nanocrystal formation shows that experimental conditions can easily be manipulated so that the growth of nanoseeds occurs at potentials that support preferential DMAP adsorption on {100} surfaces giving rise to highly anisotropic nanocrystals (nanorods, bipyramids, and nanopods). Nanopods with nearly 50 nm arm lengths are shown to form and produce a surface plasmon mode that extends well into the near IR (λ<sub>max</sub> ≈ 1350 nm). Evidence is provided of the slow, partial reduction of tetrachloroaurate to a DMAP stabilized Au<sup>I</sup> species. Shape control is achieved simply by varying the length of time, τ, that DMAP is allowed to partially reduce the Au<sup>III</sup> ions prior to the addition of the strong reducing agent, NaBH<sub>4</sub>. Thus the role of DMAP in producing anisotropic particle shapes is shown to be multifunctional. A mechanism accounting for the dependence of particle shape on τ is provided
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