Perfluorinated porphyrazines. 3. Synthesis, spectral-luminescence and electrochemical properties of perfluorinated octaphenylporphyrazinatozinc (II)
Abstract
Octakis(pentafluorophenyl)porphyrazinatozinc(II), [ZnPAF(40)], has been prepared by template cyclotetramerization of perfluorinated alpha,beta-dicyanostylbene in the presence of ZnCl2 in a melt. Influence of perfluorination of phenyl rings on spectral, electrochemical and acid-base properties of porphyrazine macrocycle is revealed by comparison with octaphenylporphyrazinatozinc(II), [ZnPA], which was prepared similarly from trans-alpha,beta-dicyanostylbene.
B3LYP DFT calculations show that perfluorination of phenyl rings stabilizes the frontier molecular orbitals of the porphyrazine macrocycle and slightly increases the HOMO-LUMO gap. As a result the reduction of the macrocycle is strongly facilitated and observed for [ZnPAF(40)] at 0.26 V vs Ag/AgCl, by 0.56 V in the less negative region as compared to [ZnPA].
Perfluorination leads to hypsochromic shift of the Q-band (lowest pi pi* transition) in the electronic absorption spectra from 633 nm for [ZnPA] to 623 nm for [ZnPAF(40)] and increases the fluorescence quantum yield Phi(F) from 0.12 to 0.19, respectively (values in THF). [ZnPAF(40)] has higher efficiency in generation of singlet oxygen (Phi(Delta) = 0.60) than [ZnPA] (Phi(Delta) = 0.37) (in THF). Introduction of 40 fluorine atoms decreases the basicity of the porphyrazine macrocycle almost by 3 orders of magnitude according to spectrophotometric titration study in CH2Cl2-CF3COOH medium.