Novel unsymmetrically substituted push-pull phthalocyanines for second-order nonlinear optics

The gamma(3 omega; omega, omega, omega) and gamma(2 omega; omega, omega, 0) hyperpolarizabilities of some novel unsymmetrically substituted phthalocya nines (Pcs) have been measured at lambda = 1.34 mu m and lambda = 1.9 mu m, respectively. The EFISH values are positive as expected from a strong orie ntational contribution, By using a two-level model including the ground and the Q-excited levels, the off-resonant dipolar beta(v)(0) component of the beta tensor has been evaluated, Values are quite significant and reach 46. 7 X 10(-30) esu for the free molecule with an extended conjugated path to t he NO2 acceptor group. The molecules containing a transition metal yield si milar values that increase with the sequence Co, Ni, Cu in correlation with the magnitude of the ground state dipole moment. THG susceptibilities are negative and much larger than those measured for similar symmetric compound s. This has been related to a dominant asymmetric contribution associated t o the Q-band which is resonant at the second-harmonic frequency. (C) 1999 E lsevier Science B.V. All rights reserved.