Advancing the Synthesis and Applications of Pyrrole-Modified Porphyrins

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Funded by the Chemical Structure, Dynamic & Mechanism B Program of the Chemistry Division, the research group led by Professor Christian Brueckner of the Department of Chemistry at the University of Connecticut will develop a number of dyes derived from the naturally occurring molecule class called porphyrins. This compound class gives blood (hemoglobin) its deep red color. Altering the molecular structure of the porphyrin slightly by insertion, replacement, or deletion of atoms at defined positions varies their optical properties. Thus, for example, dyes are derived that absorb a large portion of sunlight, making them attractive options for light-harvesting applications. Other dyes possess properties that may make them useful as contrast agents for optical imaging in medicine, a potentially notable broader scientific impact. The work begins with the development of the synthetic strategies to generate the novel dyes. Once prepared, their physical properties are evaluated. The strong interdisciplinary nature of the work provides excellent training for graduate and undergraduate students for a modern and inclusive workforce.The main objective of this grant is the development of strategies to convert porphyrins into pyrrole-modified porphyrins (PMPs), macrocycles derived from porphyrins by formally replacing at least one pyrrolic building block with a different heterocycle. Starting from meso-arylporphyrins or octaethylporphyrin, a little explored but versatile strategy will be pursued: activation of the beta position of porphyrins, followed by ring cleavage and subsequent ring-fusion. This generates PMPs containing one or two five, six, and seven-membered non-pyrrolic heterocycles and that may also incorporate extended pi-systems through beta-to-meso-phenyl linkages. The guiding hypothesis of the work is that these modifications result in drastically altered electronic properties when compared to their parent porphyrins or chlorins. Particularly with respect to their longest wavelength of absorbance and fluorescence, their hyperchromic and, in some cases, panchromic spectra, and in their efficient non-radiative relaxation processes, many PMPs possess remarkable photophysical properties of potential utility. In collaboration with specialty groups, their application in select fields will be tested. Structure-physical properties relationships will also be developed.