title: Green light-excitable naphthalenediimide acetylide-containing cyclometalated Ir(III) complex with long-lived triplet excited states as triplet photosensitizers for triplet-triplet annihilation upconversion.
abstract: Naphthalenediimide (NDI) was connected to the ligand of a cyclometalated Ir(III) complex (Ir-1) via a C≡C triple bond to enhance the absorption in the visible region and to access long-lived triplet excited states. Ir(ppy)2(bpy)[PF6] (Ir-2, ppy = 2-phenylpyridine and bpy = 2,2'-bipyridine) was used as a model complex. The photophysical properties of the complexes were studied with steady state and time-resolved spectroscopy. Ir-1 shows strong absorption in the visible region (ε = 11,000 M(-1) cm(-1) at 542 nm) and in comparison Ir-2 shows typically weak absorption in the visible region (ε < 3000 M(-1) cm(-1) above 400 nm). Room temperature near IR emission at 732 nm (Φ(P) = 0.1%) was observed for Ir-1, which is attributed to the NDI localized emissive triplet excited state, by transient absorption spectra and DFT calculations on the spin density surface. The lifetime of the NDI-localized triplet excited state is up to 130.0 μs, which is rarely reported for Ir(III) complexes. In comparison, Ir-2 shows phosphorescence at 578 nm and the triplet state lifetime is a typical value of 0.3 μs. The complexes were used as triplet photosensitizers for triplet-triplet annihilation (TTA) upconversion and an upconversion quantum yield of 6.7% was observed with Ir-1. No upconversion was observed with Ir-2 as the triplet photosensitizer at the same experimental conditions.
authors.affiliation: State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian 116012, PR China.
authors.forename: Lihua
authors.initials: L
authors.lastname: Ma
authors.forename: Song
authors.initials: S
authors.lastname: Guo
authors.forename: Jifu
authors.initials: J
authors.lastname: Sun
authors.forename: Caishun
authors.initials: C
authors.lastname: Zhang
authors.forename: Jianzhang
authors.initials: J
authors.lastname: Zhao
authors.forename: Huimin
authors.initials: H
authors.lastname: Guo
mesh_terms: D000042:Absorption; D015195:Drug Design; D007094:Imides / Q000737:chemistry*; D007495:Iridium / Q000737:chemistry*; D008027:Light; D008958:Models, Molecular; D008968:Molecular Conformation; D009281:Naphthalenes / Q000737:chemistry*; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D017319:Photosensitizing Agents / Q000138:chemical synthesis / Q000737:chemistry*; D013997:Time Factors
chemical_list: D007094:Imides; D009281:Naphthalenes; D009942:Organometallic Compounds; D017319:Photosensitizing Agents; C542131:naphthalenediimide; D007495:Iridium