Recently some phthalocynine derivatives have been reported to exhibit a strong optical limiting effect which is due
to their large reverse saturable absorption. In this report we present another close family of phthalocynine, meso-substituted
tetrabenzoporphyrins. We have employed both modified Z-scan techniques which uses a CCD camera as the detector and
picosecond transient spectroscopy to study the optical power limiting mechanism of the meso-substituted tetrabenzoporphyrin
derivatives. With the aid of a CCD detector, a two dimensional image of the beam, in the far field can be obtained directly in
the Z-scan experiments. By integrating different parts of the image, both "closed aperture" and "open aperture" information
can be calculated at the same time. In the kinetics measurements, several characteristic (ir,ir*), (,*) and (d, d) transitions
have been observed, and the absorption cross sections and the relaxation rates of each transient has been measured.