Tunable molecular configuration for significant enhancement of two-photon absorption based on novel octupolar benzoimidazole derivatives

Two novel octupolar molecules including benzoimidazole electron-accepting (A) branches and a triphenylamine electron-donating (D) center have been synthesized and characterized (p-ETBN and m-ETBN). Their photophysical and photochemical properties were investigated systematically including single-photon absorption, two-photon absorption (2PA) and charge transfer performance. Their 2PA properties have been investigated by the open aperture Z-scan technique, and the values of the 2PA cross section at 800 nm for p-ETBN and m-ETBN are ∼300 GM and ∼100 GM, respectively. Interestingly, both of them have the same D, A and π-conjugating units with only the different molecular configuration, the 2PA response of them differs by almost three times, which are found to be the different excited-state dipole moments and intramolecular charge-transfer. Our results reveal a new rule of molecular design for obtaining some excellent 2PA materials for their potential biophotonic and optoelectronic applications.