Phthalocyanine-based nonlinear optical (NLO) materials are reviewed, w
ith particular emphasis on second-order effects. The requirements on m
aterials and molecules for NLO activity are outlined before three rece
ntly studied families are briefly considered: asymmetrically substitut
ed phthalocyanines (Pcs), subphthalocyanines (Pc analogues such as R t
hat in the Figure), and triazolephthalocyanines.