Synthesis and spectroelectrochemical investigation of two tetraarylporphyrins

A free-base tetraarylporphyrin was synthesized by the [2+2] macrocyclization of a dipyrromethane derivative with 3,4,5-tris(dodecyloxy)benzaldehyde in 61% yield. The free-base porphyrin was metallated with zinc acetate in 94% conversion. The free-base and metallated porphyrins show typical intense Soret bands at 426 and 425 nm, respectively, along with the expected number and intensity of Q-bands. Both porphyrins are also fluorescent and display small Stokes shifts between 13 and 18 nm. Cyclic voltammetry established that each porphyrin underwent two reversible one-electron oxidations at 492 and 725 mV (vs Fc/Fc(+) (ferrocene reference)) for the free-base porphyrin and at 329 and 589 mV (vs Fc/Fc(+)) for the Zn-metalloporphyrin. Electron-transfer rates were also determined to fall between 1.2 x 10(-3) and 2.4 x 10(-3) cm s(-1). In addition, spectroelectrochemistry and density functional theory calculations of the oxidized products were carried out to confirm the macrocyclic ring oxidations.