The nonlinear and linear photo-physical properties of π-conjugated extensions based on difluoroboron β-diketonate complexes with terminal triphenylamines: The role of vinyl unit

Abstract

Three linear push-pull compounds comprised of difluoroboron β-diketonate and triphenylamine unit 4,6-Bis(4-(diphenylamino)phenyl)-2,2-difluoro-2H-1,3,2-dioxaborinin-1-ium-2-uide, (E)-6-(4-(Diphenylamino)phenyl)-4(4(diphenylamino)styryl)-2,2-difluoro-2H-1,3,2-dioxaborinin-1ium-2-uide and 4,6-Bis((E)-4-(diphenylamino)styryl)-2,2-difluoro-2H-1,3,2-dioxaborinin-1-ium-2-uide (ABA, ABVA, and AVBVA) have been probed by many spectroscopies. The results clarify the photo-physical property of the compounds where ABVA and AVBVA are linked with vinyl units (V). The solvent-dependent steady absorption and photoluminescence spectra data shows that the vinyl unit and the polarity of the solvent influence the photo-physical properties of the compound. Moreover, the vinyl unit would further enhance the role of the polar environment. The transient absorption measurement then offers excitation relaxation behavior. The results show that excited compounds in cyclohexene go back to the ground state through the intramolecular charge transfer (ICT) state, and the transfer lifetime from the initial excited state to the ICT state would prolong after the introduction of vinyl unit. The relaxation behavior becomes complex when cyclohexene is replaced by tetrahydrofuran. Some excited compounds go directly back to the ground state and others go back to the ground state after passing through the ICT state. In addition, two-photon PL measurements and a Z-scan technique are employed, and this confirms that these compounds have two-photon behavior, but the two-photon absorption section gradually decreases. This decrease is attributed to the spectral shifting affected by the vinyl unit.