Enhancement of two photon absorption properties and intersystem crossing by charge transfer in pentaaryl boron-dipyrromethene (BODIPY) derivatives.

Novel BODIPY derivatives containing N,N-diphenylamine, 4-methoxyphenyl, 2,4-dimethoxyphenyl, triphenylamine, and 1-pyrene moieties were designed and synthesized for the first time by employing the palladium-catalyzed Suzuki-Miyaura coupling on pentaaryl boron dipyrromethene compounds. The effect of various moieties and charge transfer on linear and nonlinear optical absorption was investigated. It was found that moieties with strong electron donor properties and long conjugation lengths increase charge transfer and enhance intersystem crossing in the investigated compounds. Besides, the investigated compounds showed strong two photon absorption properties at near infrared wavelengths (800 nm and 900 nm), which is required for two photon photodynamic therapy. Two photon absorption cross section values were found to be 83, 454, 331, 472 and 413 GM for , , , and compounds at 800 nm wavelength, respectively. The highest two-photon absorption cross-section value was obtained for the compound containing a triphenylamine moiety due to its more efficient charge transfer characteristics. Strong two-photon absorption properties in the near infrared region, efficient intersystem crossing and heavy atom free nature of the investigated compounds make them good candidates for two photon photodynamic therapy applications. We believe that this work will be one of the leading studies for two-photon photodynamic therapy applications of pentaaryl BODIPY derivatives.

Two photon absorption properties of four coordinated transition metal complexes of tetraarylazadipyrromethene compounds.

New tetraarylazadipyrromethene metal complexes with four coordinate metals (cobalt(ii), nickel(ii), copper(ii) and zinc(ii)) and with three moieties (4-methylphenyl,4-methoxyphenyl and 1-naphthyl) were designed and synthesized targeting applications utilizing two photon absorption. The effects of metals with filled or unfilled d orbitals and substituents with various electron donor properties on the charge transfer mechanism and two photon absorption properties of tetraarylazadipyrromethene compounds were investigated by ultrafast pump-probe spectroscopy and open aperture Z-scan experiments as well as density functional theory (DFT) calculations. Ultrafast transient absorption spectra provide evidence of an efficient photoinduced intramolecular charge transfer between the ligand and metals which is independent of filled or unfilled d orbitals of metals. Although zinc has filled d orbitals, its complexes possess an absorption maximum including a shoulder which is attributed to partial ligand to metal L(π) → M(d*) charge transfer character (LMCT). Due to the charge transfer mechanism, metal complexes of tetraarylazadipyrromethene compounds exhibited two photon absorption properties in the femtosecond regime at 800 nm wavelength. The greatest two photon absorption cross section value was measured as 2690 GM for Zn(L(2))2 and 2374 GM for Co(L(3))2 complexes.