Abstrakt
The spontaneous adsorption of [N,N',N '',N'''-tetramethyltetra-3,4-pyridino-porphyrazino-Co(II)] ([CoTmtppa](4+)) from an aqueous solution onto highly ordered pyrolytic graphite (HOPG) was followed by in situ electron paramagnetic resonance (EPR). The solution of [CoTmtppa](4+)(CH3SO4)(4)(-) exhibits no EPR signal in the temperature range from 120 to 293 K.
At room temperature, on the other hand, the EPR spectra of both spontaneously adsorbed and powdered [CoTmtppa](4+) were unambiguously identified by the spectral simulations and quantum chemical calculations. The results indicated different geometries for the powdered and adsorbed samples.
The time evolution of the EPR spectrum of [CoTmtppa](4+) and that of HOPG during the adsorption made it possible to obtain a kinetic picture of the process. Finally, the structure and the redox stability of the magnetically active [CoTmtppa](4+) molecular film on HOPG was studied by atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), UV-vis backscattering spectroscopy, and cyclic voltammetry.
Our findings reveal that EPR is simultaneously capable of following the structural changes of ionic phthalocyanine as well as the spin state of the conducting electrons (CEs) of HOPG, whereas the spin state of the CEs does not change upon adsorption.