Synthesis and spectral properties of N4, N3S, and N2S2 porphyrins containing one, two, three, and four meso-furyl groups

Porphyrins with N4, N3S, and N2S2 cores having one, two, three, and four furyl groups at the meso-positions were synthesized by following various methodologies and characterized by using mass spectrometry, NMR spectroscopy, elemental analysis, absorption, and fluorescence spectroscopic techniques. NMR studies indicated that by replacing the meso-aryl groups with meso-furyl groups, the β-pyrrole and β-thiophene protons of porphyrins experienced considerable downfield shifts, supporting the alteration of π-delocalization of porphyrins on the introduction of meso-furyl groups. The absorption and emission bands of porphyrins experienced red shifts on the introduction of meso-furyl groups and the magnitude of red shifts vary linearly with the number of meso-furyl groups. Thus, the spectral studies supported a systematic alteration in spectral properties on successive introduction of meso-furyl groups.