Date of Award
Doctor of Philosophy
A free-base porphyrin dye, 4-(5-carboxyphenyl)-10,15,20-tritolylporphyrin (TTPa) formed well-behaved monomolecular films at the air-water interface. The carboxylic acid was the hydrophilic portion, and became ionized at subphase pH > 7.3.;The presence of two or more two-dimensional crystalline phases in these films on the aqueous surface under certain conditions was inferred from the observation of visible, inhomogeneous specular reflection from the films.;A spectroscopic study of Langmuir-Blodgett monolayers indicated three different species existed in the films as a function of the pH to which the subphase was buffered. One species was assigned as the monomer; the others as aggregates. One of the aggregates exhibited an unusual absorption spectrum and was postulated to exist in an environment where motion was restricted.;Langmuir-Blodgett films transferred from buffer-free water underwent a rapid reorganization; after 24 hours the absorption spectrum resembled that of a thin sublimed film. These spectra were of amorphous films, which contained a wide range of aggregates.;The action spectrum of the photocurrent for photovoltaic cells constructed from amorphous multilayers agreed qualitatively with their absorption spectrum, establishing that the photocurrent did not arise preferentially from one of the aggregates, unlike the fluorescence which resulted only from the monomer.;The interpretation of the dark current-voltage characteristics varied with the number of monolayers n. For thin films (n = 1 and n = 3) the current was due to tunnelling. For thick films (n = 29) the characteristic could be fitted using either a modified Shockley equation (suggesting TTPa acted as a p-type semiconductor) or a combination of Schottky and Frenknel-Poole emission (suggesting TTPa acted as an insulator). The former interpretation was consistent with the observed rectification, while the latter was in agreement with the magnitude of the conductivity of the films.;The power conversion efficiency of these cells was quite low (4 x 10('-4)% for incident white light of 3 W m('-2)) due to their large internal resistance, resulting from an unfavorable orientation of the porphyrin rings.
Bardwell, Jennifer Ann, "Spectroscopic And Photovoltaic Properties Of Monolayer Films Of A Porphyrin Dye" (1983). Digitized Theses. 1288.