Post-Modification of meso-meso-Linked Porphyrin Arrays by Iridium and Rhodium Catalyses for Tuning of Energy Gap

meso-meso-Linked diporphyrins fabricated with multiple unsaturated carboxylic acid groups are efficiently synthesized by the use of transition-metal catalysis. Iridium-catalyzed direct borylation of meso-meso-linked diporphyrins furnish multi-borylated diporphyrins with high regioselectivity. Then, the introduction of alpha,beta- or alpha,beta,gamma,delta-unsaturated ester functions to the diporphyrins is achieved through rhodium-catalyzed Heck-type addition of the borylated diporphyrins to acrylate or 2,4-pentadienoate esters. Saponification of the esters to the corresponding acids is accomplished in high yields. The post-modification of diporphyrin 6 smoothly provides a water-soluble multiporphyrin array 1 in 84% total yield in 3 steps. This functionalization significantly affects the electronic properties of the porphyrins, resulting in different energy levels of each porphyrin unit. The absorption and fluorescence spectra indicate efficient energy transfer in the porphyrin dimers.