Porphyrin Deposition Induced by UV Irradiation

Simple irradiation by UV light of porphyrin TpyP and its zinc(II) and manganese(III) metal derivatives in chlorinated solvents leads to the deposition on silica of mesoscale aggregates. The process is due to the photochemical decomposition of the solvent with generation of HCl, which causes the precipitation of a protonated form. The morphology of the resulting objects is driven by the nature of the inserted metal ion. We describe a simple method to deposit aggregates of acid TpyP having sizes from hundreds of nanometers up to tenths of microns from a chlorinated solvent solution on a silica surface. After repetitive scanning with a diode-array spectrophotometer in a solution of TpyP ( c= 10 -5 M) in CH2Cl2, the strong Soret band at 417 nm gradually decreases in intensity, whereas a new broad feature increases at about 485 nm. Very simple and convenient method to deposit porphyrin aggregates and crystals from halogenated solvents on silica substrate has been developed. The possibility of tuning the photophysical properties of the mesoaggregates on changing the metal ions or the substituents on the porphyrins opens the way to different potential applications, for example, in the field of electrooptical devices