D-A type phenanthridine derivatives with aggregation-induced enhanced emission and third-order nonlinear optical properties for bioimaging

Materials with aggregation-induced emission (AIE) and their applications have still been hot spot in material science. At present work, three novel D-A type phenanthridine derivatives (Sa, Sb and Sc) had been synthesized and fully characterized. The relationships between the structures and photophysical properties of the three compounds were investigated with aid of experimental and theoretical calculation methods. The results shows there are only ICT and π-π* transitions in the three compounds. Additionally, the three compounds showed excellent aggregation-induced one- and two-photon emission enhancement (AIEE) properties. To better understand the AIEE properties, dynamic light scattering (DLS) and scanning electron microscopy (SEM) were performed, explaining that the small and uniform particles are beneficial to improve fluorescence emissions. Furthermore, the enhanced aggregation-induced emission was deeply understood based on crystal structural information. Except, third-order nonlinear optical properties also were systematically determined by open/close aperture Z-scan methods using tunable femtosecond laser. The results revealed that Sb possesses largest two-photo absorption (2PA) coefficient (β = 0.349 cm/GW) and cross sections (σ = 1669.306 GM) compared to the others. Lastly, the three compounds also can be applied in cell imaging because of their good biocompatibility and lower cytotoxicity.