SYNTHESIS OF LINEAR AMPHIPATHIC PORPHYRIN DIMERS AND TRIMERS - AN APPROACH TO BILAYER-LIPID MEMBRANE-SPANNING PORPHYRIN ARRAYS

A modular building-block approach has been developed for the construct ion of linear amphipathic porphyrin arrays. The reaction of meso-(trif luoromethyl)dipyrromethane and an aldehyde under the conditions of the two-step room temperature porphyrin synthesis affords the trans-subst ituted porphyrin (13-56% yields). A similar reaction with two differen t aldehydes provides access to porphyrins bearing two different functi onal groups. An ethyne porphyrin and an iodo porphyrin (either free ba se or zinc) are selectively joined via Pd(0)-catalyzed coupling reacti ons, affording a linear array with porphyrins in defined metalation st ates. Coupling of a zinc-porphyrin bearing iodo and ester groups with a free base porphyrin bearing ethyne and ester groups yielded the zinc -free base porphyrin dimer. Coupling of a bis-ethyne porphyrin with a porphyrin bearing iodo and ester groups afforded the porphyrin trimer. Cleavage of the esters yielded the amphipathic porphyrin dimer and tr imer arrays. The arrays with adjacent zinc and free base porphyrins un dergo efficient electronic energy transfer. Both amphipathic porphyrin arrays have been incorporated into L-ol-phosphatidylcholine vesicles. This versatile synthetic strategy provides access to a family of porp hyrin arrays for studies of photophysical processes in supramolecular assemblies.