One-Step Synthesis and Characterization of Difunctionalized N-Confused Tetraphenylporphyrins

Three disubstituted N-confused porphyrins (2−4) were prepared in ca. 4% yield using a one-pot synthesis. These porphyrins bear 3,5-di-tert-butylphenyl groups substituted at the C₅ and C₂₀ meso positions and para-substituted (Br, NO₂, ethynyl) phenyl groups at the C₁₀ and C₁₅ meso positions. The specific orientation of the aryl rings around the macrocycle in porphyrin 2 was definitively determined using a combination of 1D (¹H and ¹³C) and 2D (gHMQC and gHMBC) NMR spectroscopy. The absorption spectra of 2−4 in CH₂Cl₂ and dimethylacetamide are similar to those of N-confused tetraphenylporphyrin in the same solvents but have Soret and Q-bands that are shifted to lower energies. Steady-state fluorescence measurements revealed Q_x(0,0) and Q_x(0,1) bands similar in energy to the unsubstituted NCPs 1i and 1e. The fluorescence quantum yield results for two of these NCPs (2, 4) are atypical of porphyrin behavior and are being further investigated by time-resolved spectroscopy.