Photophysical and Electrochemical Studies of Β-Functionalized Arylaminoporphyrins

Abstract

β-functionalized porphyrins possess interesting photophysical, electrochemical and conformational properties that can be useful for applications in the area of non-linear optics, catalysis and anion sensing.1 β-nitration, β-formylation and β-halogenation of porphyrins have been utilized to prepare starting compounds which can be further converted into mixed β-substituted porphyrins.2 Only a few porphyrins having carbon-heteroatoms at their β-position are known and their electronic and redox properties have not been explored in great detail as compared to other β-functionalized porphyrins. The versatility of this synthetic approach to achieve new mixed β-functionalized porphyrins was previously demonstrated in the synthesis of medicinally related compounds as well as new types of ligands and DSSC materials.3 The substitution of an arylamino group onto a porphyrin through C-N bond formation provides a good porphyrin substrate which differs from previous systems in term of its chemical and photophysical properties. In the present paper, we report the synthesis and electrochemical characterization of β-arylaminodibromoporphyrins shown in Chart 1. Five arylamino porphyrins, represented as (Br2NH(X)PorM), were fully characterized by UV-Vis, Fluorescence, 1H NMR spectroscopy and cyclic voltammetry techniques. DFT studies indicate planar to moderate non-planar conformations of the porphyrins, revealing the effect of the different arylamines on the porphyrin core. Absorption spectra exhibited much broader and blue shifted Soret bands with fewer Q bands as compared to the precursor and other tri-subtituted porphyrins.2 Reduced emission spectra and lower lifetimes were also observed due to the presence of two bromo group. Electrochemical studies were performed under different solution conditions and the data compared with that of other tri-substituted porphyrins. Changing the arylamino group from phenylamine to naphthylamine and then to 4-nitro/cyanophenylamine significantly altered the redox potentials of these porphyrins. In this presentation, we will discuss the structural, spectral and electrochemical properties of the newly synthesized β-arylamino functionalized porphyrins.