Synthesis, Characterization and Weak Intramolecular Interactions of Porphyrins Bearing Nucleobases

5, 10, 15‐Triphenyl‐20‐|2‐[α‐(adenine‐9) acetylamino]| phenyl porphyrin (1), 5,10,15‐triphenyl‐20‐|2‐[α‐(cytosine‐l)acetylamino]| phenyl porphyrin (2), 5, 10, 15‐triphenyl‐20‐|4‐[α‐(cytosine‐1)ethoxy]| phenyl porphyrin (3) and their zinc complexes Zn‐1, Zn‐2 and Zn‐3 have been prepared and characterized by 1H NMR spectra, elemental analyses, electronic absorption spectra and mass spectra (FAB). Intramolecular π‐π interactions and intramolecular metal‐π interaction for 1, 2, Zn‐1, and Zn‐2 have been investigated by several methods. 1H NMR studies demonstrate that the porphyrin π‐system in 1 and 2 is parallel to the adenine and the cytosine aromatic ring, respectively. The electronic absorption spectral properties of free porphyrin derivatives and their zinc complexes have been compared with those of H2TPP and ZnTPP. The results show that the UV‐vis spectra of 1 and 2 are the same as that of H2TPP, whereas the spectra of their zinc complexes show 7 nm red shifts of the Soret bands compared to that of ZnTPP. The emission spectra of Zn‐1 and Zn‐2 are independent of excitation wavelength. From combination of the evidence of absorption and emission spectra it is suggested the existence of intramolecular metal‐π interaction in Zn‐1 and Zn‐2. The results of conformational analysis agreed quite nicely with that of experiments, thus it was further to validate the experimental conclusions.