ABSTRACT
The chemistry of ring-expanded porphyrins has gained growing focus because of their properties potentially suitable for a number of novel practical applications. Expanded, isomeric, and contracted porphyrins are named by a combination of the number of conjugated p-electrons, pyrroles, and meso-atoms. The structural difference from porphyrins is the complete absence of meso-carbons. The ability to fine-tune the wavelength of absorptions based on structural modification such as ring annelation would enhance the utility of the compounds for practical applications. π-Expanded and core-modified cyclo[n]pyrroles, ring-expanded porphyrins with no meso-bridges have been successfully synthesized via oxidative coupling of 2,2'-bipyrroles with appropriate template anion and Suzuki—Miyaura coupling of terpyrrole analogues. The enhanced absorptions could prove useful for optelectronic and photofunctional devices in near-infrared dye applications. Challenging efforts are now underway to achieve selective synthesis of cyclo[n]pyrroles consisting of more than 10 pyrroles or a combination of pyrroles and other heterocycles in porphyrin chemistry.
