Dicyanomethylene-functionalized s-indacene-based D-π-A-π-D dyes exhibiting large near-infrared two-photon absorption cross-section

A series of centrosymmetric chromophores with D-π-A-π-D molecular architecture has been synthesized and characterized with respect to their third-order nonlinear optical (NLO) properties. The investigated compounds feature novel central electron acceptor fragments composed of derivatives of s-indacene-1,3,5,7(2H,6H)-tetraone (Janus dione), in which the carbonyls have been substituted by either two or four dicyanomethylene groups. Due to the increased electron acceptor strength, up to twofold increase in two-photon absorption (2 PA) cross-section is observed for the dyes in comparison to the structural analogues based on the parent compound. The best performing dye exhibits intensive 2 PA absorption band in 1000–1300 nm range with a peak cross-section value of 11,000 GM. Optical limiting was successfully demonstrated using the compound, marking the presented chemical design as a promising direction for optical power-limiting applications in the important near-infrared (NIR) spectral region. Electronic Supplementary Information (ESI) available: experimental procedures, results of quantum chemical calculations, NMR spectra.