Excited-state absorption and third-order optical nonlinearities in symmetric pi-electron organic molecules

Excited-State Absorption (ESA), Two-Photon Absorption (TPA) and the third-order polarizability gamma(omega; omega, omega, - omega) have been investigated for a model dichloride derivative of a symmetrically substituted benzylidene analine (SBAC), using a multielectron configuration-interaction procedure. The calculations indicate that SBAC exhibits ESA across the visible region of the spectrum, but that it is not as extensive as for molecules such as the phthalocyanines. The magnitude of the third-order polarizability is dominated by resonance enhancement from a very strong A(g) --> B-u one-photon absorption. The calculated off-resonance value for gamma(omega; omega, omega, - omega) suggests that SBAC is a potential candidate for ultrafast switching applications.