Excited-state investigations of meso-mono-substituted-(amino-ferrocenyl)porphyrins: Experimental and theoretical approaches

Abstract

The spectroscopic study and characterization of mono-(amino-ferrocenyl) porphyrins has increased during the last years. These molecules can be synthesized in such a way that their linear and nonlinear optical parameters are modulated, opening the possibility for new applications, such as in photodynamic therapy. In this work, we perform a spectroscopic characterization of a group of five free-base porphyrins, three of them having a C6F4 group attached to an amino-ferrocene moiety through a −NH(CH2)nNH− spacer, in which n = 2, 4 or 6. These three molecules differ by the size of the aliphatic chain. For this study, we employ linear as well as nonlinear optical spectroscopic techniques, such as the Z-Scan and time resolved fluorescence. Decay times, absorption cross-sections and quantum yields were determined, and the results suggest that, for this group of molecules, the differences in the aliphatic chain sizes joining the ferrocenyl unit to the C6F4 group at the para-position aryl ring do not influence significantly the optical parameters. Further, DFT calculations confirm that the UV–vis absorbance and the associated electronic transitions are not affected by the size of the aliphatic chain spacers. Thus, it is possible to state that these molecules can interact with biomolecules through the ferrocene unit while keeping their optical properties unchanged.