Investigation of two rational routes for preparing p-phenylene-linked porphyrin trimers

Multiporphyrin arrays with p-phenylene linkers, aryl groups at the non-linking meso positions, and no beta -substiments are attractive constructs for light-harvesting applications. Condensation of a free base porphyrin-benzaldehyde and 5-mesityldipyrromethane (10 mM each) in CH2Cl2 containing 100 mM TFA at room temperature for 30-40 min followed by oxidation with DDQ afforded a p-phenylene-linked porphyrin trimer in 36% yield. Suzuki coupling of an iodo-porphyrin and a bis(dioxaborolane)-porphyrin (20 and 10 mM, respectively) in toluene/DMF (2:1) containing K2CO3 (8 equiv.) at 90-95 degreesC for similar to 20 h afforded the same trimer in 66% yield. The former route was used to prepare a diethynyl substituted p-phenylene-linked porphyrin trimer. While the two routes are somewhat complementary in scope, both are convergent and proceed in a rational manner. (C) 2001 Elsevier Science Ltd. All rights reserved.