title: 1D polymeric platinum cyanoximate: a strategy toward luminescence in the near-infrared region beyond 1000 nm.
abstract: We report the synthesis and properties of the first representative of a new class of PtL2 complexes with ambidentate mixed-donor cyanoxime ligands [L = 2-cyano-2-oximino-N,N'-diethylaminoacetamide, DECO (1)]. Three differently colored polymorphs of "Pt(DECO)2" (3-5) were isolated, with the first two being crystallographically characterized. The dark-green complex [Pt(DECO)2]n (5) spontaneously forms in aqueous solution via aggregation of yellow monomeric complex 3 into the red dimer [Pt(DECO)2]2 (4), followed by further oligomerization into coordination polymer 5. A spectroscopic and light-scattering study revealed a "poker-chips"-type 1D polymeric structure of 5 in which units are held by noncovalent metallophilic interactions, forming a Pt---Pt wire. The polymer 5 shows a broad absorption at 400-900 nm and emission at unusually long wavelengths in the range of 1000-1100 nm in the solid state. The near-infrared (NIR) emission of polymer 5 is due to the formation of a small amount of nonstoichiometric mixed-valence Pt(II)/Pt(IV) species during synthesis. A featureless electron paramagnetic resonance spectrum of solid sample 5 recorded at +23 and -193 °C evidences the absence of Pt(III) states, and the compound represents a "solid solution" containing mixed-valence Pt(II)/Pt(IV) centers. Exposure of KBr pellets with 5% 5 to Br2 vapors leads to an immediate ∼30% increase in the intensity of photoluminescence at 1024 nm, which confirms the role and importance of mixed-valence species for the NIR emission. Thus, the emission is further enhanced upon additional oxidation of Pt(II) centers, which improves delocalization of electrons along the Pt---Pt vector. Other polymorph of the "Pt(DECO)2" complex--monomer--did not demonstrate luminescent properties in solutions and the solid state. An excitation scan of 5 embedded in KBr tablets revealed an emission only weakly dependent on the wavelength of excitation. The NIR emission of quasi-1D complex 5 was studied in the range of -193 to +67 °C. Data showed a blue shift of λmax and a simultaneous increase in the emission line intensity with a temperature rise, which is explained by analogy with similar behavior of known quasi-1D K2[Pt(CN)4]-based solids, quantum dots, and quantum wells with delocalized carriers. The presented finding opens a route to a new class of platinum cyanoxime based NIR emissive complexes that could be used in the design of novel NIR emitters and imaging agents.
authors.affiliation: Department of Chemistry, Missouri State University (MSU) , Temple Hall 456, Springfield, Missouri 56897, United States.
authors.forename: Danielle R
authors.initials: DR
authors.lastname: Klaus
authors.forename: Matthew
authors.initials: M
authors.lastname: Keene
authors.forename: Svitlana
authors.initials: S
authors.lastname: Silchenko
authors.forename: Mikhail
authors.initials: M
authors.lastname: Berezin
authors.forename: Nikolay
authors.initials: N
authors.lastname: Gerasimchuk
mesh_terms: D000081:Acetamides / Q000737:chemistry*; D005021:Ethylamines / Q000737:chemistry*; D007259:Infrared Rays; D049449:Luminescence; D008163:Luminescent Measurements; D015394:Molecular Structure; D009944:Organoplatinum Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011108:Polymers / Q000138:chemical synthesis / Q000737:chemistry*
chemical_list: C000602192:2-cyano-2-oximino-N,N'-diethylaminoacetamide; D000081:Acetamides; D005021:Ethylamines; D009944:Organoplatinum Compounds; D011108:Polymers