Photochemical Sciences Ph.D. Dissertations

The Excited State Behavior of Iminium Derivatives and Their Reduced Forms

Date of Award

2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (Ph.D.)

Department

Photochemical Sciences

First Advisor

Ksenija Glusac

Second Advisor

Alexander Tarnovsky (Committee Member)

Third Advisor

R. Marshall Wilson (Committee Member)

Fourth Advisor

Zhaohui Xu (Committee Member)

Abstract

Photoinduced heterolytic bond cleavage is at the heart of many photochemical researches in renewable energy and biocatalysis. This dissertation outlines studies of photochemical heterolytic reactions involving the ‾OH and H‾ release from the iminium derivatives. In specific, the heterolytic properties of the iminium salt derivatives, such as N(5)-ethyl-4a-hydroxyflavin (Et-FlOH), 9-hydroxy-10-methyl-9-phenyl-9,10-dihydroacridine (AcrOH), and 10-methyl-9-phenyl-9,10-dihydroacridine (AcrH), were studied using transient absorption (TA) spectroscopy method. In the first part, the heterolytic property of Et-FlOH is studied, which is also related to understanding the photocatalytic mechanism of the bacterial bioluminescence. The heterolysis is not observed from the TA study of Et-FlOH except a fast S1→S0 decay. Combining with the results of time-dependent density functional theory calculations of Et-FlOH excited-states, a S1→S0 conical intersection (CI) is approved as the most important role for this fast decay. This identification proves that a rigid bio-condition is required to inhibit the formation of CI for this photocatalytic bacterial bioluminescence. In the second part, the excited state behavior of AcrOH is studied in different solvents via UV-vis TA spectroscopy. A fast heterolytic cleavage (τ = 108 ps) coupled with a ‾OH release is observed in the protic solvent, while intersystem crossing is observed in the aprotic solvent. This photoinduced heterolytic behavior exhibits the characteristic required for pOH jump catalytic research, such as the conformational changes in DNA/RNA and the release of drugs from host molecules. In the last part, a photoinduced hydride release from AcrH was investigated using TA spectroscopy. The hydride release is postulated to be a stepwise electron/H-atom transfer process from the triplet excited state of AcrH, and O2 acts as an important electron acceptor in this process. These results show the high potential that, coupled with an inorganic catalyst, AcrH can be used as a photocatalyst in a bi-catalyst catalytic H2 production system.

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