Pyrene derivatives as broadband nonlinear optical material: Magnitude and mechanism of transient refraction

Two asymmetric pyrene derivatives (E)-1-(4-(dimethylamino)-3-(pyren-1-yl)prop-2-en-1-one) (DAPP-1) and (E)-3-(4-(diemthylamino)phenyl)-1-(pyren-1-yl)prop-2-en-1-one (DAPP-2) were synthesized to access lossless broadband nonlinear refraction. Femtoseconds Z-scan from 600 nm to 1030 nm showed positive third-order nonlinear refractive index with high linear transmission (>90%). Both compounds had ≥2.5 figure of merit (F) at 1030 nm, while DAPP-2 held >1 F value in a wide spectral region. Mechanism of ultrafast refraction under off & on-resonant regime were investigated via degenerate & non-degenerate pump-probe with phase object, respectively. Results indicate pure response of bound electrons under off-resonance and excited-state enhanced nonlinear refraction under on-resonance. All the study suggested that optical nonlinearity in pyrene derivatives has been underestimated and molecules like DAPP-2 possess the potential to be further optimized into superior broadband nonlinear refractive materials.