Noncentrosymmetric triazolephthalocyanines as second-order nonlinear optical materials

Three substituted triazolephthalocyanines, i.e., intrinsically noncentrosymmetric and planar phthalocyanine derivatives, have been synthesized and characterized. They present significant (similar to 10(-28) esu) quadratic hyperpolarizabilities, beta(HRS) and beta(EFISH), respectively measured at lambda = 1.34 mu m and II = 1.907 mu m. Moreover, the ratio beta(EFISH)(2)(1.907 mu m)/[beta(HRS)(2)(1.34 mu m)] markedly decreases when increasing the donor strength of the substituents at the isoindole rings (opposite to the triazole moiety), This has been attributed to the corresponding increase in the ratio mu(01)(x)/mu(01)(z) between the x (perpendicular to the molecular axis) and z (parallel to the molecular axis) in-plane components of the Q-band transition moment. This result suggests that the dipolar versus octupolar contribution to beta could be varied and controlled by suitable selection of the donor/acceptor strength of the substituents.