Rationally designed two-photon absorption compounds based on benzoxazole derivatives: structure-property relationships and bio-imaging applications.

A new series of benzoxazole-based two-photon absorption (2PA) chromophores (T1-5) were synthesized and fully characterized. Among them, T1-3 are linear donor (D)-π-acceptor (A) type fluorophores with various electron-donating groups, while T4 and T5 are multi-branched compounds stemming from T3. Their photophysical properties have been systematically investigated, and the two-photon absorption properties indicate that the highest 2PA cross-section (σ) is 2702 GM for T5 (in DMF). Structure-property relationships of the chromophores are comprehensively discussed based on their optical properties, crystal structures and density functional theory (DFT) calculations. In addition, a two-photon fluorescence cell imaging experiment demonstrates the potential bio-application of T1-5 with good photostability and low cytotoxicity.