Date of Award
1994
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Abstract
An upgraded version of the program SIMPFIT is used to carry out deconvolution analyses on the uv-visible absorption and magnetic circular dichroism (MCD) spectra of zinc phthalocyanine, ZnPc({dollar}-{dollar}2), and the ring reduced anion radical of zinc phthalocyanine, (ZnPc({dollar}{lcub}-3{rcub})\rbrack\sp-.{dollar} A detailed study of the temperature dependence of the absorption and MCD spectra of ZnPc({dollar}-{dollar}2) shows that a significant fraction of the spectral intensity observed at room temperature can be assigned as 'hot' bands. This results in a significant discrepancy in the absorption and MCD band widths of the major transitions. Spectral band deconvolution was therefore carried out on data recorded at cryogenic temperatures. The analysis of ZnPc({dollar}-{dollar}2) provides definite evidence for an {dollar}\rm n\to\pi\sp\*{dollar} transition just to the blue of the lowest lying {dollar}\pi\to\pi\sp\*{dollar} transition. The origin of the vibrational bands associated with the lowest lying {dollar}\pi\to\pi\sp\*{dollar} transition is resolved enabling a complete description of the optical spectrum. An extensive analysis of the optical absorption and MCD spectra of the anion radical of zinc phthalocyanine, (ZnPc({dollar}{lcub}-3{rcub})\rbrack\sp-,{dollar} is described. Novel photochemical formation of the ring reduced (ZnPc({dollar}{lcub}-3{rcub})\rbrack\sp-{dollar} from (hydrazine)Zn(II)Pc({dollar}-{dollar}2) is reported for reactions carried out at room temperature using visible wavelength light and hydrazine as the electron donor. Phosphorescence and fluorescence lifetime studies of ZnPc({dollar}-{dollar}2) show that the photoexcited (hydrazine)ZnPc({dollar}-{dollar}2) complex reacts via the triplet state to form the ring reduced anion radical, (ZnPc({dollar}{lcub}-3{rcub})\rbrack\sp-.{dollar} Absorption and MCD spectra of the radical anion species have been obtained at both room and cryogenic temperatures. The complete lack of temperature dependence assignable to orbital degeneracies in the low temperature MCD spectrum proves that the {dollar}\rm\sp2E\sb g{dollar} ground-state of (ZnPc({dollar}{lcub}-3{rcub})\rbrack\sp-{dollar} is split into nondegenerate components at least 800 cm{dollar}\sp{lcub}-1{rcub}{dollar} apart. It is proposed that the coupled effects of the loss of aromaticity with the addition of the 19th {dollar}\pi{dollar}-electron, Jahn-Teller distortion, and nonsymmetric solvation of the ring lead to a change in molecular geometry from the D{dollar}\rm\sb{lcub}4h{rcub}{dollar} of ZnPc({dollar}-{dollar}2) to C{dollar}\rm\sb{lcub}2v{rcub}{dollar} for (ZnPc({dollar}{lcub}-3{rcub})\rbrack\sp-.{dollar} The first complete assignment of the optical spectrum of any porphyrin or phthalocyanine anion radical is proposed based on a {dollar}\rm\sp2B\sb1{dollar} ground-state and supported by results from extensive deconvolution calculations. Hot bands are much more pronounced in the spectral data of the (ZnPc({dollar}{lcub}-3{rcub})\rbrack\sp-{dollar} than in the spectral data of the parent ZnPc({dollar}-{dollar}2) and are associated with interactions between the solvent, the Pc({dollar}-{dollar}3) ring, and vibronic bands associated with the split ground-state. The fact that band widths calculated to fit the absorption spectrum increase in magnitude as a function of the transition energy from 10,000 cm{dollar}\sp{lcub}-1{rcub}{dollar} to 33,000 cm{dollar}\sp{lcub}-1{rcub}{dollar} allows the classification of sets of bands to one of 5 major electronic transitions, namely, Q between 750-1000 nm, {dollar}\rm n\to\pi\sp\*{dollar} between 580-750 nm, {dollar}\pi\sp\*\to\pi\sp\*{dollar} between 430-650 nm, B1 and B2 between 300 and 450 nm. Spectroelectrochemical cells have been designed which enabled the measurement of the first reported example of MCD spectra recorded on a species generated in situ inside the sample bore of a superconducting magnet. The assignment of (ZnPc({dollar}{lcub}-3{rcub})\rbrack\sp-{dollar} is extended to the spectra of more highly reduced anion species and anion species of other MPc complexes. A comparison is made between the energies of the major transitions of the {dollar}\pi{dollar}-system in the optical spectra of the neutral, oxidised and reduced species of MgPc.
Recommended Citation
Mack, John Douglas, "Magnetic Circular Dichroism Spectroscopy Of Phthalocyanine Anions" (1994). Digitized Theses. 2442.
https://ir.lib.uwo.ca/digitizedtheses/2442