Highly Efficient Triplet Photosensitizers: A Systematic Approach to the Application of Ir-III Complexes containing Extended Phenanthrolines

摘要

A series of Ir-III complexes, based on 1,10-phenanthroline featuring aryl acetylene chromophores, were prepared and investigated as triplet photosensitizers. The complexes were synthesized by Sonogashira cross-coupling reactions using a "chemistry- on-the-complex" method. The absorption properties and luminescence lifetimes were successfully tuned by controlling the number and type of light-harvesting group. Intense UV/Vis absorption was observed for the IrIII complexes with two light-harvesting groups at the 3- and 8-positions of the phenanthroline. The asymmetric IrIII complex (with a triphenylamine (TPA) and a pyrene moiety attached) exhibited the longest lifetime. Red emission was observed for all the complexes in deaerated solutions at room temperature. Their emission at low temperature ( 77 K) and nanosecond time-resolved transient difference absorption spectra revealed the origin of their triplet excited states. The singlet-oxygen (O-1(2)) sensitization and triplet-triplet annihilation (TTA)-based upconversion were explored. Highly efficient TTA upconversion (phi(UC)=28.1%) and O-1(2) sensitization (phi(Delta)=97.0%) were achieved for the asymmetric Ir-III complex, which showed intense absorption in the visible region (lambda(abs)=482 nm, epsilon=50900 M(-1)cm(-1)) and had a long-lived triplet excited state (53.3 mu s at RT).