Date of Award


Degree Type


Degree Name

Doctor of Philosophy


Time-resolved fluorescence lifetime measurements of 5-(4-carboxyphenyl)-10,15,20-tritolylporphyrin (TTPa) with dioleoylphosphatidylcholine (DOPC) in mixed Langmuir-Blodgett (LB) films on quartz slides were performed at two different laboratories in an attempt to create a standard system for future monolayer fluorescence work. TTPa in the mixed LB film exhibited a simpler and longer decay profile than for a pure TTPa monolayer. At a DOPC/TTPa molar ratio of 50:1, the decay consisted primarily of one lifetime of 10.7 {dollar}\pm{dollar} 0.2 ns. Simplification of the decay and lengthening of the lifetime was attributed to reduction of TTPa aggregate formation in the film. This effect is also seen in fluorescence and absorption spectra.;In addition the photoelectrochemistry of pure TTPa monolayers deposited on SnO{dollar}\sb2{dollar} semiconductor slides was studied. Measurements included capacitance versus voltage, current versus voltage, light intensity, electrolyte pH, supersensitizer concentration, and wavelength of excitation. Mott-Schottky plots and current-voltage measurements indicated that the monolayer formed was not insulating but allowed electrolyte to pass through it. Anodic photocurrents of up to 2{dollar}\mu{dollar}A/cm{dollar}\sp2{dollar} were observed for a single monolayer at low electrolyte pH. The photocurrent was highly dependent on supersensitizer concentration at low pH and rather insensitive at high pH. It is postulated that direct injection of electrons from the first excited singlet state of the porphyrin is operative at high pH whereas trapping of the electron by surface states occurs at low pH.;Cathodic photocurrents were also seen for electrolytes containing only supporting electrolyte. This was attributed to reduction of adsorbed oxygen by the excited porphyrin.



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