Porphyrin Research at the Evergreen State College: The Synthesis, Separation, Isolation and Characterization of Di-functional meso-substituted Porphyrins (An Advancement toward Solar Energy Harvesting Technologies)

Introduction The process of photosynthesis has interested humanity for eons. It is arguably the most important biological process on earth and is responsible for a large portion of our current energy needs.

Structural Formulas:.

Chlorophyll: In plants, the green pigment chlorophyll absorbs light energy. Chlorophyll is a porphyrin molecule that resides in the thylakoid membrane of the chloroplast. And

Porphyrins: Natural pigments containing a fundamental skeleton of four pyrrole nuclei united through the alpha positions by four methine groups to form a macrocylic structure ( IUPAC Compendium of Chemical Terminology 2nd Edition)

Photovoltaic cell: When sunlight strikes the surface of these cells an electrical field provides both momentum and direction to electrons that results in a flow of current. Image: {

Photovoltaic cell: These cells can be connected electrically in series and/or parallel circuits to produce higher, currents, voltage and power levels. Image: {

Gratzell cell: A proposed design for a solar cell which utillizes porphyrins. Image: {

Synthesis: For the initial synthesis of these porphyrins, the Rothemund Method was utilized. This technique was first developed during the 1930’s and later improved upon in the 70’s by the Adler research group at the University of Pennsylvania.

Synthesis: For the initial synthesis of these porphyrins, the Rothemund Method was utilized. This technique was first developed during the 1930’s and later improved upon in the 70’s by the Adler research group at the University of Pennsylvania.

The synthesis of meso-Tri(Tolyl) Mono(4-carboxyphenyl) Porohyrin

Isolation: When two types of aldehydes are used, this reaction mechanism will produce five different structural isomers.

Column Chromatography: The technique of column chromatography was developed in 1906 by the Italian-born Russian botanist Mikhail Tswett. During the process, a mixture of compounds is dissolved into a liquid phase and allowed to flow through a column of powdered calcium carbonate in a vertical glass tube.

Isolation: The roto-vap, or rotary evaporator, is a device that allows a liquid to be evaporated in a controlled manner

NMR Spectroscopy: NMR is a technique that was developed in 1945 by American physicists Felix Bloch and Edward Mills Purcell.

This technique is based on the principle that a spinning photon generates a magnetic field.

During NMR, a substance is placed in a strong magnetic field causing the protons to align with the stronger field in a lower energy state

A radio wave is passed through the substance supplies the resonance frequency needed to excite the protons to the higher energy state

The use of NMR spectroscopy for structural determination arises because protons in a substance experience slightly different magnetic fields.

Example of a NMR Spectrum: meso-Tetra (Tolyl) Porphyrin NMR spectrum

UV-Vis Spectroscopy: When a sample is irradiated with UV light, it causes the promotion of an electron from a ground electronic state to an excited electronic state Image: {

Absorption is described by the log of radiant power entering the sample, P 0, divided by the radiant power leaving the sample, P, and is directly proportional to the path length, l, and the concentration, c, of the absorbing species multiplied by,  a constant of proportionality, called the absorbtivity or epsilon value.

Because of the way absorption is defined, The total power absorbed by a molecule in the Uv-Vis region of the EM spectrum can be calculated by tacking the integral of the derivative of the power absorbed with respect to the change in wavelength and multiplying it by the change in wavelength.

Example of a UV-Vis Spectrum: meso-Tetra (Tolyl) Porphyrin Uv-Vis spectrum

Other Applications of Porphyrins 1. Current electronics research is focused on producing computers that are faster and more compact ( The intriguing possibility of making electronic components from single molecules or small groups of molecules is becoming a large area of research. Another very active area of research is computers that use light, rather than electrons, as the medium for carrying information. In principle, light-based computers have several advantages over traditional designs ) Proffesor Deven Gust of ASU Image: {

Other Applications of Porphyrins 2. Light has a very high energy content, and cause serious damage to living organisms. For example, sunlight absorbed by photosynthetic chlorophyll will sometimes cause tissue damage in plants. Furthermore, It has been shown that certain porphyrins will localize in cancerous tumor tissue. Illumination of this area results in photochemical damage which destroys the tumor while leaving surrounding tissue undamaged. Image: {

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