Date of Award

2023

Document Type

Thesis

Degree Name

MS in Chemistry

Department

Chemistry

First Advisor

Charles M Fortmann

Second Advisor

Joseph Serafin

Third Advisor

Tianchan Jiang

Abstract

The absorption, light scattering, and anti-Stoke’s fluorescence of chlorophyll and closely related sodium copper chlorophyllin were examined in various solutions with a wide range of refractive index and permittivity. It was evident that radiative photo electron decay corresponded to low permittivity solvents, but not to solvent refractive index. Additionally, non-radiative decay was dominant in high permittivity solvents. The properties suggest evolution has provided plants with an ability to redirect light to the chlorophyll in the high permittivity (water) photosynthesis center. Exploratory solar cells exploiting lifetime switching were developed and tested, wherein strong photovoltaic response was exhibited, along with the unique property of charge storage owing to an insulating transport layer and reverse current transport paths being made inoperative. These solar cells are characterized by photo-electron transfer to an interface for collection and were able to record photo-electron charge transfer from the photo-active molecules (e.g., chlorophyll) to the electrode by tracking the stored potential of the solar cell by high impedance voltmeter, while the device was in open circuit. Analysis of the voltage rise under monochromatic laser diode illumination was consistent with approximately one mono layer of photo-active molecules nearest to the electrode generating charge transfer to the electrode. While the devices did not produce useful amounts of electric power, it was recognized that the absorption spectrum was indeed related to charge transferred and that the devices could measure exceedingly small photo generated current. Subsequently, the device was used to carefully probe molecular charge transfer. Previous reports raised concerns that zinc oxide and/or titanium oxide photo electron emission may catalyze free radial formation that in turn, increases cancer risk. The molecular photoemission was observed in chlorophyll A, sodium copper chlorophyllin, and nicotine. While chlorophyll A and chlorophyllin displayed electron photoemission over a broad range of the visible spectrum including the near UV, nicotine only produced photo emitted electrons in the near UV. The surprisingly strong nicotine near UV emission was comparable to that of chlorophyll A and chlorophyllin. The results suggest a physical basis for the reported association between squamous cell carcinoma and smoking.

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