title: Electrochemical, spectroscopic, and photophysical properties of structurally diverse polyazine-bridged Ru(II),Pt(II) and Os(II),Ru(II),Pt(II) supramolecular motifs.
abstract: Five new tetrametallic supramolecules of the motif [{(TL)(2)M(dpp)}(2)Ru(BL)PtCl(2)](6+) and three new trimetallic light absorbers [{(TL)(2)M(dpp)}(2)Ru(BL)](6+) (TL = bpy = 2,2'-bipyridine or phen = 1,10-phenanthroline; M = Ru(II) or Os(II); BL = dpp = 2,3-bis(2-pyridyl)pyrazine, dpq = 2,3-bis(2-pyridyl)quinoxaline, or bpm = 2,2'-bipyrimidine) were synthesized and their redox, spectroscopic, and photophysical properties investigated. The tetrametallic complexes couple a Pt(II)-based reactive metal center to Ru and/or Os light absorbers through two different polyazine BL to provide structural diversity and interesting resultant properties. The redox potential of the M(II/III) couple is modulated by M variation, with the terminal Ru(II/III) occurring at 1.58-1.61 V and terminal Os(II/III) couples at 1.07-1.18 V versus Ag/AgCl. [{(TL)(2)M(dpp)}(2)Ru(BL)](PF(6))(6) display terminal M(dπ)-based highest occupied molecular orbitals (HOMOs) with the dpp(π*)-based lowest unoccupied molecular orbital (LUMO) energy relatively unaffected by the nature of BL. The coupling of Pt to the BL results in orbital inversion with localization of the LUMO on the remote BL in the tetrametallic complexes, providing a lowest energy charge separated (CS) state with an oxidized terminal Ru or Os and spatially separated reduced BL. The complexes [{(TL)(2)M(dpp)}(2)Ru(BL)](6+) and [{(TL)(2)M(dpp)}(2)Ru(BL)PtCl(2)](6+) efficiently absorb light throughout the UV and visible regions with intense metal-to-ligand charge transfer (MLCT) transitions in the visible at about 540 nm (M = Ru) and 560 nm (M = Os) (ε ≈ 33,000-42,000 M(-1) cm(-1)) and direct excitation to the spin-forbidden (3)MLCT excited state in the Os complexes about 720 nm. All the trimetallic and tetrametallic Ru-based supramolecular systems emit from the terminal Ru(dπ)→dpp(π*) (3)MLCT state, λ(max)(em) ≈ 750 nm. The tetrametallic systems display complex excited state dynamics with quenching of the (3)MLCT emission at room temperature to populate the lowest-lying (3)CS state population of the emissive (3)MLCT state.
authors.affiliation: Department of Chemistry, Virginia Tech, 107 Davidson Hall, Blacksburg, Virginia 24061-0212, USA.
authors.forename: Jessica D
authors.initials: JD
authors.lastname: Knoll
authors.forename: Shamindri M
authors.initials: SM
authors.lastname: Arachchige
authors.forename: Guangbin
authors.initials: G
authors.lastname: Wang
authors.forename: Krishnan
authors.initials: K
authors.lastname: Rangan
authors.forename: Ran
authors.initials: R
authors.lastname: Miao
authors.forename: Samantha L H
authors.initials: SL
authors.lastname: Higgins
authors.forename: Benjamin
authors.initials: B
authors.lastname: Okyere
authors.forename: Meihua
authors.initials: M
authors.lastname: Zhao
authors.forename: Paul
authors.initials: P
authors.lastname: Croasdale
authors.forename: Katherine
authors.initials: K
authors.lastname: Magruder
authors.forename: Brian
authors.initials: B
authors.lastname: Sinclair
authors.forename: Candace
authors.initials: C
authors.lastname: Wall
authors.forename: Karen J
authors.initials: KJ
authors.lastname: Brewer