Photophysics and Excited-State Properties of Cyclometalated Iridium(III)-Platinum(II) and Iridium(III)-Iridium(III) Bimetallic Complexes Bridged by Dipyridylpyrazine.

Title Photophysics and Excited-State Properties of Cyclometalated Iridium(III)-Platinum(II) and Iridium(III)-Iridium(III) Bimetallic Complexes Bridged by Dipyridylpyrazine.
Authors Y.J. Cho; S.Y. Kim; C.Min Choi; N.Joon Kim; C.Hoon Kim; D.Won Cho; H.J. Son; C. Pac; S.Ook Kang
Journal Inorg Chem
DOI 10.1021/acs.inorgchem.7b00384
Abstract

We investigated the electrochemical and excited-state properties of 2,3-bis(2-pyridyl)pyrazine (dpp)-bridged bimetallic complexes, (L)2Ir-dpp-PtCl [1, L = 2-(4',6'-difluorophenyl)pyridinato-N,C(2) (dfppy); 2, L = 2-phenylpyridinato-N,C(2) (ppy)] and [(L)2Ir]2(dpp) [3, L = dfppy; 4, L = ppy] compared to monometallic complexes, (L)2Ir-dpp (5, L = dfppy; 6, L = ppy) and dpp-PtCl (dpp-Pt(II)Cl2; 7). The single-crystal X-ray crystallographic structures of 1, 3, 5, and 6 showed that 1 and 3 have approximately coplanar structures of the dpp unit, while the noncoordinated pyridine ring of dpp in 5 and 6 is largely twisted with respect to the pyrazine ring. We found that the properties of the bimetallic complex significantly depended on the electronic and geometrical modulations of each fragment: (1) electronic structure of the main L (C^N) ligand in an iridium chromophore (L = dfppy or ppy) and (2) planarity of the bridging ligand (dpp). Their electrochemical and photophysical properties revealed that efficient electron-transfer processes predominated in the bimetallic systems regardless of the second metal participation. The low efficiencies of photoluminescence of dpp-bridged Ir-Pt and Ir-Ir bimetallic complexes (1-4) could be explained by assuming the involvement of crossing to platinum- and iridium-based d-d states from the emissive state. Such stereochemical and electronic situations around dpp allowed thermally activated crossing to platinum- and iridium-based d-d states from the emissive triplet metal-to-ligand charge-transfer ((3)MLCT) state, followed by cleavage of the dpp-Pt and (L)2Ir-dpp bonds. The transient absorption study further confirmed that the planarity of the dpp bridging ligand, which was defined as the magnitude of tilt between the pyridine ring and pyrazine, had a direct correlation with the degree of nonradiative decay from the emissive iridium-based (3)MLCT to the Ir d-d or Pt d-d state, leading to photoinduced dissociation of bimetallic complexes. From the dissociation pattern of metal complexes analyzed after photoirradiation, we found that their dissociation pathways were directly related to the quenching direction (either Ir d-d or Pt d-d) with a significant dependency on the relative (3)MLCT levels of the (L)2Ir-dpp component.

Citation Y.J. Cho; S.Y. Kim; C.Min Choi; N.Joon Kim; C.Hoon Kim; D.Won Cho; H.J. Son; C. Pac; S.Ook Kang.Photophysics and Excited-State Properties of Cyclometalated Iridium(III)-Platinum(II) and Iridium(III)-Iridium(III) Bimetallic Complexes Bridged by Dipyridylpyrazine.. Inorg Chem. 2017;56(9):53055315. doi:10.1021/acs.inorgchem.7b00384

Related Elements

Iridium

See more Iridium products. Iridium (atomic symbol: Ir, atomic number: 77) is a Block D, Group 9, Period 6 element with an atomic weight of 192.217. The number of electrons in each of iridium's shells is [2, 8, 18, 32, 15, 2] and its electron configuration is [Xe] 4f14 5d7 6s2. Iridium Bohr ModelThe iridium atom has a radius of 136 pm and a Van der Waals radius of 202 pm. Iridium was discovered and first isolated by Smithson Tennant in 1803. In its elemental form, Iridium has a silvery white appearance. Iridium is a member of the platinum group of metals.Elemental Iridium It is the most corrosion resistant metal known and is the second-densest element (after osmium). It will not react with any acid and can only be attacked by certain molten salts, such as molten sodium chloride. Iridium is found as an uncombined element and in iridium-osmium alloys. Iridium's name is derived from the Greek goddess Iris, personification of the rainbow, on account of the striking and diverse colors of its salts.

Platinum

See more Platinum products. Platinum (atomic symbol: Pt, atomic number: 78) is a Block D, Group 10, Period 6 element with an atomic weight of 195.084. The number of electrons in each of platinum's shells is [2, 8, 18, 32, 17, 1] and its electron configuration is [Xe] 4f14 5d9 6s1. The platinum atom has a radius of 139 pm and a Van der Waals radius of 175 pm. Platinum Bohr ModelElemental PlatinumPlatinum was discovered and first isolated by Antonio de Ulloa in 1735. It is one of the rarest elements in the earth's crust, occurring at a concentration of only 0.005 ppm. Platinum is found uncombined as a free element and alloyed with iridium as platiniridium. In its elemental form, platinum has a grayish white appearance. It is highly resistant to corrosion: the metal does not oxidize in air at any temperature. It is generally non-reactive, even at high temperatures. The origin of the name "platinum" comes from the Spanish word platina, meaning silver.