Photo-Switchable and Wavelength Selective Axial Ligation of Thiol-Appended Molecules to Zinc Tetraphenylporphyrin: Spectral and Charge Transfer Kinetics Studies

Axial ligation property of metalloporphyrins has got vital importance in the architecture of donor–acceptor dyads, 3D cages and modular assemblies made up of porphyrins. Nitrogenous ligands have been extensively used in this regard. In this paper, we made a unique attempt to axially ligate thiol-appended molecule to tetraphenylporphyrinato zinc(II), (ZnTPP). Taking the advantage of photoexcitation of metalloporphyrins, axial ligation of 1-dodecanethiol (DDT) to ZnTPP in the presence of visible light was invented. This has been ascertained by recording the charge transfer between ZnTPP and DDT. Photoinduced axial ligation of DDT to ZnTPP under visible light was studied by varying the wavelength and intensity of the light source. The axial ligation reaction was found to be photoswitching and wavelength selective. The binding constant of the ZnTPP–DDT complex was found to be comparable with that of ligands bind to ZnTPP though nitrogen. The consequence of the axial ligation on the HOMO and LUMO and the photoinduced charge transfer kinetics of the planar chromophore, ZnTPP were studied. Scanning electrochemical microscope was used to extract the heterogeneous charge transfer constant values in the case of ZnTPP and ZnTPP–DDT at the film/electrolyte solution.