Synthesis of 1,4-phenylene-bridged linear porphyrin arrays

1,4-Phenylene-bridged, linear porphyrin arrays including the dimer, trimer, pentamer, heptamer and nonamer have been synthesized by acid-catalysed condensation of formyl-substituted porphyrins with bis(3-ethyl-4-methylpyrrol-2-yl)methane in moderate yields. The molecular length of the nonamer is estimated to be as long as ca. 122 Angstrom. The Soret bands of both zinc complexes and doubly protonated free base porphyrins are split depending upon the number of the porphyrins, which can be explained in terms of exciton coupling theory. With an increase in the number of the porphyrins, the fluorescence spectra become broader and red-shifted without significant decrease in the fluorescence quantum yield, reflecting their stretched conformations that do not allow the formation of a singlet-excitation-energy trapping site.