| Title
| - A Class of Luminescent Cyclometalated Alkynylgold(III)Complexes: Synthesis, Characterization, andElectrochemical, Photophysical, and Computational Studiesof [Au(C∧N∧C)(C⋮CR)] (C∧N∧C = κ3C,N,C Bis-cyclometalated2,6-Diphenylpyridyl)
|
| Abstract
| - A new class of luminescent cyclometalated alkynylgold(III) complexes, [Au(RC∧N(R‘)∧CR)(C⋮CR‘ ‘)], i.e., [Au(C∧N∧C)(C⋮CR‘ ‘)] (HC∧N∧CH = 2,6-diphenylpyridine) R‘ ‘ = C6H51, C6H4Cl-p2, C6H4NO2-p3, C6H4OCH3-p4, C6H4NH2-p5, C6H4C6H13-p6, C6H137, [Au(tBuC∧N∧CtBu)(C⋮CC6H5)] 8(HtBuC∧N∧CtBuH = 2,6-bis(4-tert-butylphenyl)pyridine), and [Au(C∧NTol∧C)(C⋮CC6H4−C6H13-p)] 9(HC∧NTol∧CH = 2,6-diphenyl-4-p-tolylpyridine), have been synthesized and characterized. The X-ray crystalstructures of most of the complexes have also been determined. Electrochemical studies show that, ingeneral, the first oxidation wave is an alkynyl ligand-centered oxidation, while the first reduction couple isascribed to a ligand-centered reduction of the cyclometalated ligand with the exception of 3 in which thefirst reduction couple is assigned as an alkynyl ligand-centered reduction. Their electronic absorption andluminescence behaviors have also been investigated. In dichloromethane solution at room temperature,the low-energy absorption bands are assigned as the π−π* intraligand (IL) transition of the cyclometalatedRC∧N(R‘)∧CR ligand with some mixing of a [π(C⋮CR‘ ‘) → π*(RC∧N(R‘)∧CR)] ligand-to-ligand charge transfer(LLCT) character. The low-energy emission bands of all the complexes, with the exception of 5, are ascribedto origins mainly derived from the π−π* IL transition of the cyclometalated RC∧N(R‘)∧CR ligand. In thecase of 5 that contains an electron-rich amino substituent on the alkynyl ligand, the low-energy emissionband was found to show an obvious shift to the red. A change in the origin of emission is evident, and theemission of 5 is tentatively ascribed to a [π(C⋮CC6H4NH2) → π*(C∧N∧C)] LLCT excited-state origin. DFTand TDDFT computational studies have been performed to verify and elucidate the results of theelectrochemical and photophysical studies.
|
