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| Author(s): |
Antonio Carlos Sant'Ana
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Paulo. |
| Institution: | Universidade de São Paulo (USP). Conjunto das Químicas (IQ e FCF) (CQ/DBDCQ) |
| Defense date: | 2005-10-05 |
| Examining board members: |
Márcia Laudelina Arruda Temperini;
Carlos José Leopoldo Constantino;
Maria Cecília Barbosa da Silveira Salvatori;
Susana Inês Cordoba de Torresi;
Teresa Benita Iwasita de Vielstich
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| Advisor: | Márcia Laudelina Arruda Temperini |
| Abstract | |
In this Thesis Surface-Enhanced Raman Scattering (SERS) and resonance Raman spectroscopy were used for monitoring the adsorption and faradaic behavior of squaric acid and its derived species. In addition, the charge transfer salt of squarate and tetrathiofulvalene and the copolymers of squarate and pyrroles were also studied. Another theme developed in this study was the manufacturing of. high performance SERS-active substrates. SERS technique has been a field of great interest since the detection of a single molecule Raman spectrum in 1997. The development of high perforrnance SERS-active substrates depends on the proper manipulation of nanostructured metal surfaces, and order to acquire know-how in the synthesis of such substrates. Ag and Au island films as well as colloid substrates were prepared and compared with electrode surfaces SERS activated by oxidation-reduction cycles. The enhancement factor obtained for such films is comparable to those observed in electrodes. The squarate anion, product of the double deprotonation of squaric acid, shows substantial charge delocalization, being largely used in the synthesis of conducting organic materiaIs. The vibrational characterization of squaric acid, hydrogen-squarate, squarate as well as its radical was carried out from the SERS data. Based on the experimental data an adsorption mechanism of such species on Au electrodes and Au or Ag islands was proposed. SERS results also show that squaric acid adsorbed on Au is decomposed in a process catalyzed by the metal surface, although in solution it proves to be a very stable specles. The vibrational characterization of an electrochemically forrned charge transfer salt between tetrathiofulvalene radical-cation and squarate radical-anion was done based on the SERS data of tetrathiofulvalene and its oxidation species. The large resonance Raman and SERS enhancement factors of tetrathiofulvalene preclude the detection of the squarate species in the charge transfer salt. Two polysquaraines: poly(1-methylpyrrole-co-squaric acid) and poly(1-dodecylpyrrole-co-squaric acid) were synthesized and characterized by resonance Raman, SERS and Electron Paramagnetic Resonance Spectroscopy (EPR) techniques. The results lead us to propose a polymeric structure different from that present in the literature. Our data showed a delocalized organic radical in the polymeric matrices together with dications similar to those present in polypirrole and protonated squarate anion. (AU) | |