Meso-Meso and -Meso Imine-Bridged Thien-2-yl Porphyrin Dyads: Synthesis, Spectral and Electrochemical Investigations

Imine-bridged meso-meso and beta-meso unsymmetrical thien-2-yl porphyrin dyads were synthesized by condensation of meso- and beta-formyl derivatives of 5,10,15,20-tetrakis(3-methylthien-2-yl)porphyrinato nickel (II), Ni3MeThP with 5-(5-Aminothien-2-yl)-10,15,20-triphenylporphyrinato nickel(II), Ni5AThPP in the presence of lanthanum(III)triflate catalyst in toluene at 120 C-degrees for 8 h. The structural, photophysical, and redox properties were investigated by H-1 NMR, UV/Vis spectral, and electrochemical analysis. The near coplanarity of the linker thien-2-yl group with the central porphyrin pi-system, which can influence the electron delocalization of these molecules, is explained using electronic spectroscopy and cyclic voltammetry. The stronger electronic interaction between the two porphyrin units and the increased nonplanarity of the macrocycle brought about by the beta-meso imine bridging is indicated by the larger shift of redox potentials in the dyad-2 as compared to the dyad-1 system. The results of the present investigation reveal that the two distinct porphyrin units in dyads interact via their near planar thien-2-yl linker.