Date of Award


Degree Type


Degree Name

Doctor of Philosophy


The organizing properties of surface-active porphyrins can be employed to obtain large area, ordered arrays of electroactive organic molecules. The design, synthesis, and characterization of two families of surface active porphyrins, possessing variety of side chains, is described. These materials are solid at room temperature and exhibit well-behaved monomolecular films at an air-water interface.;In compressed monolayers, the porphyrin ring appears to be oriented so that the plane of the ring is perpendicular to the surface. The surface pressure-molecular area isotherms change with the length and nature of the side chains in a manner which suggests that a long side chain allows the porphyrin rings to acquire the most ordered packing. A rigid chain structure was found to restrict the orientational flexibility of the porphyrin rings and hence restricted them to acquire well-ordered monolayer.;The solid state photophysical properties of these materials are strongly dependent on their degree of order. Spectroscopic studies of single monolayer films transferred to quartz and SnO{dollar}\sb2{dollar} slides using the Langmuir-Blodgett technique indicate that increasing the order in porphyrin monolayers leads to increasing spectral shifts in absorption and to decreasing fluorescence quantum yields. On the SnO{dollar}\sb2{dollar} semiconductor surface, the monolayers exhibit an enhanced fluorescence quenching. This is interpreted as evidence for isoenergetic electron transfer from the porphyrin to the semiconductor. An approximate interfacial electron transfer rate (k{dollar}\sb{lcub}\rm et{rcub}{dollar}) was estimated on the basis of the fluorescence yields on quartz and SnO{dollar}\sb2{dollar} surfaces, respectively.;The surface active porphyrins deposited onto SnO{dollar}\sb2{dollar} semiconductor surface exhibit an unusual photoelectrochemical effect: a substantial and stable photocurrent/photovoltage is generated in modified photoelectrode cells which possess porphyrins with electron rich side chains. This is interpreted as resulting from enhanced electron injection at the illuminated interface, resulting from an enhanced through bond electron tunnelling in the electron rich side chains.;An enhanced photocurrent quantum yield was exhibited by all the compounds on diluting their monolayers with dioleoylphosphatidylcholine (DOPC), a non fluorophore surface active compound. This is interpreted as resulting from minimization of the aggregate mediated quenching, which enhances interfacial isoenergetic electron transfer and hence increases the photocurrent yield.



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