Date

Spring 4-23-2020

Document Type

Honors Project

Department

Chemistry/Biochemistry

First Advisor

Dr. Femia

Abstract

Synthesis and Characterization of Bay-Annulated Indigo Derivatives as Ligands for Photoactive Metal Complexes

Jacob Mayer1, Denise Femia1

1. La Salle University, Department of Chemistry and Biochemistry

Indigo-based chromophores are of interest for organic photovoltaics due to their light absorption properties and tunability. Indigo exhibits a high molar extinction coefficient which allows for a small amount of material to absorb a large amount of energy. Research in organic photovoltaics is important for the development of alternative sources of energy. Unlike traditional silicon photovoltaics, synthetic modifications can be made to indigo to alter its excited state lifetime, absorption, and energy levels. Although indigo has a short-lived excited state due to intramolecular proton transfer, the excited state lifetime can be extended through annulation at the bay position. This disrupts hydrogen bonding which was the cause of the proton transfer. Another effect of this is the shrinking of the HOMO-LUMO gap. This causes the indigo derivative to absorb lower energy photons that make up a large portion of the sun’s radiation spectrum. The result of this is increased efficiency of the organic photovoltaic that is able to compete with traditional silicon photovoltaics. Different derivatives can be synthesized by varying the acid chloride used in the bay annulation reaction. The second bay position is not annulated so that it can be left open to add as a ligand to a metal center. Due to a ligand-to-ligand excited state the molecule is expected to have a long-lived excited state and red-shifted absorption. The absorption spectra and molar extinction coefficients of the different indigo derivatives were tested. Metal complexes were synthesized using first row transition metals such as zinc, copper, and nickel. The derivatives were characterized via NMR, UV-vis and infrared spectroscopy. Cyclic voltammetry is used to determine the energetic properties of the materials. The results of this work will be presented.

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