Conformational flexibility of chlorin macrocycles. Structural determinations and theoretical calculations of benzochlorin, a meso-dimethyl chlorin and a nickel chlorin

X-ray structures of three chlorins with different peripheral substituents are reported. The conformations of the molecules range from nearly planar to severely puckered and illustrate the multi-conformational surfaces that chlorins can adopt. These results further demonstrate the skeletal flexibility of porphyrin derivatives and reinforce the premise that conformational variations can modulate the physical and chemical properties of porphinoids in vitro and in vivo (Barkigia et al., J. Am. Chem. Soc., 1988, 110, 7566)