αα- and αβ-Zinc-meso-A2B2-tetraarylporphyrins with large optical responses to triethylamine

Abstract

Synthesis and separation of αα- and αβ-meso-A₂B₂-zinc(II) tetraarylporphyrin atropisomers with A = mesityl and B = ortho-phenylethynyl-phenyl are reported. Both isomers exhibit large optical responses upon axial NEt₃ coordination which are visible to the human eye and could therefore be beneficial for the design of smart amine sensing materials. The larger spectral changes as compared to Zn(TPP) are attributed to pronounced distortions of the porphyrin π-system due to steric interactions of the coordinating amine with the porphyrin periphery. This effect as well as the coordination site of NEt₃ at the αα-isomer have been studied by NMR experiments and were rationalized by DFT calculations and NSD analyses. The solubility in non-polar solvents is greatly enhanced as compared to Zn(TPP), especially of the αα-isomer. This is explained by analysis of the solid state structures as derived from partial single crystal X-ray diffraction studies.