The main objective of this proposal is the continuation of our program to develop strategies to convert porphyrins into pyrrole-modified porphyrins (PMPs). PMPs are macrocycles derived from porphyrins by formally replacing at least one pyrrolic building block with a different heterocycle. Starting from meso-arylporphyrins or octaethylporphyrin, a relatively little explored but most successful and versatile strategy will be pursued: activation of the β‑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. They may also incorporate extended π-systems through β-to-meso-phenyl linkages.
The guiding hypothesis of the work – supported by our earlier 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 physical properties of potential utility. We will evaluate the (photo)physical and chemical properties of the PMPs. This data will be correlated with their structural parameters such as degree of saturation, bulk of the substituents, degree of non-planarity, and conformational flexibility.