Fluorene as the π–spacer for new two-photon absorption chromophores

We report herein the design and synthesis of two new quadrupolar D–π–A–π–D chromophores containing diphenyl amine and dicyanobenzene or 2,1,3-benzothiadiazole as electron donor (D) and acceptor (A), respectively, which are bridged by fluorene linkage (π). The introduction of coplanar fluorenes is highly beneficial for the enhancement of two-photon absorption (TPA), where 1b displays a TPA cross section (σ2) of up to 1975±207 GM.