Synthesis and spectroscopic studies of axially ligated aluminium(III)-p-methyl-meso-tetraphenylporphyrins

Abstract

Treatment of p-methyl-meso-tetraphenylporphyrin (p-CH3TPP) with aluminium(III) acetylacetonate (Al(acac)3) and phenol affords the corresponding axially ligated aluminium(III)-p-methyl-meso-tetraphenylporphyrin (Al(III)-p-CH3TPP). The separation and isolation of these derivatives have been achieved through chromatographic methods. The free base porphyrin and its axially ligated Al(III) derivatives are characterized by various spectroscopic techniques. 1H NMR spectra shows that the protons of the phenolic rings axially attached to the central metal ion are merged with the protons of the tetraphenyl ring of the porphyrin. The visible spectrum of axially ligated Al(III)p-methyl-meso-tetraphenylporphyrins show two bands, i.e., Q-bands. In axially ligated Al(III) derivatives, B and Q-bands exhibit a red shift on increasing the polarity of the solvent. The emission bands of axially ligated compounds are blue-shifted compared to free-base porphyrin but in the presence of an electron-accepting group axially attached to Al(III), the emission spectra is marginally red-shifted compared to other porphyrin compounds.