Synthesis and photophysical properties of novel pyridine fused chlorophyll a derivatives

Tandem reactions of methyl pyropheophorbide a with paraformaldehyde, reactive methylene compounds, and/or ammonium acetate provided novel pyrido[2,3-n]chlorophylls in good yields as the first examples of pyridine fused chlorophyll a derivatives, which displayed near-infrared absorptions (748–766 nm) with unusually broadened Q bands and small electrochemical HOMO-LUMO gaps (1.89–2.02 eV).