Synthesis and Spectroscopic and Biological Activities of Zn(II) Porphyrin with Oxygen Donors

Results of investigation of the physicochemical properties of zinc complexes containing substituted phenols as axial ligand having general formula [X-Zn-t(p-CH₃) PP] [where X = different phenolates as axial ligand] in impurity-free organic solvent are presented. The four-coordinated zinc porphyrin accepts one axial ligand in 1 : 1 molar ratio to form five-coordinated complex, which is purified by column chromatography and characterized by physicochemical, biological evaluation and TGA/DTA studies. Absorption spectra show two principal effects: a red shift for phenols bearing substituted electron releasing groups (−CH₃, −NH₂) and blue shift for phenols bearing electron withdrawing groups (−NO₂, −Cl) relative to Zn-t(p-CH₃) PP, respectively. ¹H NMR spectra show that the protons of the phenol ring axially attached to the central metal ion are merged with the protons of the porphyrin ring. Fluorescence spectra show two fluorescence peaks in the red region with emission ranging from 550 nm to 700 nm. IR spectra confirm the appearance of Zn-N_Por and Zn-O vibrational frequencies, respectively. According to the thermal studies, the complexes have a higher thermal stability and the decomposition temperature of these complexes depends on the axial ligation. The respective complexes of X-Zn^II-t(p-CH₃) PP were found to possess higher antifungal activity (up to 90%) and higher in vitro cytotoxicity against human cancer cells lines.

Multiple photosynthetic reaction centers composed of supramolecular assemblies of a zinc porphyrin dendrimer with pyridylnaphthalenediimide

Multiple photosynthetic reaction centers have successfully been constructed using a supramolecular complex of zinc porphyrin dendrimer [D(ZnP)16] with pyridylnaphthalenediimide (PyNIm) in benzonitrile. The apparent formation constant determined from the fluorescence quenching of the singlet excited state of porphyrin moieties by PyNIm is significantly larger than that determined from the UV-vis spectral change. This indicates that efficient energy migration occurs between the porphyrin units of the dendrimer prior to the electron transfer from the singlet excited state of zinc porphyrin to PyNIm. The charge-separated (CS) state has been successfully detected as the transient absorption spectrum in the laser flash photolysis. The CS lifetime of in the supramolecular complex of D(ZnP)16 with PyNIm was determined to be 0.83 ms at 298 K.

Photoinduced electron transfer in a supramolecular triad system composed of ferrocene-zinc porphyrin-pyridylnaphtha-lenediimide

A supramolecular ferrocene-zinc porphyrin-pyridylnaphthalenediimide triad is formed by coordinating the pyridine entity of pyridylnaphthalenediimide with the zinc ion of a ferrocene-zinc porphyrin dyad in benzonitrile. The fluorescence of the zinc porphyrin moiety is efficiently quenched by photoinduced electron transfer from the singlet excited state of the zinc porphyrin moiety to the naphthalenediimide moiety. This is followed by subsequent electron transfer from the ferrocene moiety to the zinc porphyrin radical cation to produce the final charge-separated state, ferricenium ion-zinc porphyrin-naphthalenediimide radical anion, which is successfully detected as a transient absorption spectrum in the laser flash photolysis. The decay of the charge-separated state obeys first-order kinetics irrespective of the initial concentration of the charge-separated state to afford a long lifetime (320 μs). This is the first example of a supramolecular triad that has a long lifetime as compared with the charge-separated state lifetime of the component dyad.