Recently we synthesized 3,8,13,18-tetrachloro-2,7,12,17-tetramethoxyporphyrin and its metallo-derivatives . The
free-base molecule is unique owing to the presence of an electron donating methoxy group and electron withdrawing
chloro group on the adjacent β- positions of each pyrrole moiety. We could synthesize these molecules through two
different routes; the first route provided pure isomer, albeit in low yield, whereas the second route provided mixture of
isomers with higher yield . Herein we report the third-order nonlinear optical properties of these porphyrins obtained
from Z-scan measurements using ~40 fs, 800 nm pulses. Open aperture data confirmed the presence of saturable
absorption whereas the closed aperture data indicated a positive nonlinearity. We have compared the data of the pure
isomer with that of the mixture of isomers.