Second-order nonlinear optical (NLO) materials have played a very important role in laser technology since the invention of laser. As to the organic NLO materials, the chromophores are the key component. To tune the nonlinearity-transparency trade-off in organic NLO chromophores, several promising strategies were attempted, including the introduction of heterocyclic rings, dual (mutiple) functionalizations and utilization of the interactions between chromophore moieties. In this article, recent progress in this field is reviewed.

Key words: second-order nonlinear optical effect, chromophore, molecular first-order hyperpolarizability, transparency