A Class of Luminescent Cyclometalated Alkynylgold(III) Complexes: Synthesis, Characterization, and Electrochemical, Photophysical, and Computational Studies of [Au(CNC)(C≡C-R)] (CNC = κ~3C,N,C Bis-cyclometalated 2,6-Diphenylpyridyl)

摘要

A new class of luminescent cyclometalated alkynylgold(III) complexes, [Au(RCN(R′)CR)(C≡ CR″)], i.e., [Au(CNC)(C≡CR″)] (HCNCH = 2,6-diphenylpyridine) R″ = C_6H_5 1, C_6H_4-CI-p 2, C_6H_4-NO_2-p 3, C_6H_4-OCH_3-p 4, C_6H_4-NH_2-p 5, C_6H_4-C_6H_(13)-p 6, C_6H_(13) 7, [Au(~tBuCNC~tBu)(C≡CC_6H_5)] 8 (H~tBuCNC~tBuH = 2,6-bis(4-tert-butylphenyl)pyridine), and [Au(CNTolC)(C≡CC_6H_4-C_6H_(13)-p)] 9 (HCNTolCH = 2,6-diphenyl-4-p-tolylpyridine), have been synthesized and characterized. The X-ray crystal structures of most of the complexes have also been determined. Electrochemical studies show that, in general, the first oxidation wave is an alkynyl ligand-centered oxidation, while the first reduction couple is ascribed to a ligand-centered reduction of the cyclometalated ligand with the exception of 3 in which the first reduction couple is assigned as an alkynyl ligand-centered reduction. Their electronic absorption and luminescence 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 cyclometalated RCN(R′)CR ligand with some mixing of a [π(C≡CR″) → π~*(RCN(R′)CR)] ligand-to-ligand charge transfer (LLCT) character. The low-energy emission bands of all the complexes, with the exception of 5, are ascribed to origins mainly derived from the π-π~* IL transition of the cyclometalated RCN(R′)CR ligand. In the case of 5 that contains an electron-rich amino substituent on the alkynyl ligand, the low-energy emission band was found to show an obvious shift to the red. A change in the origin of emission is evident, and the emission of 5 is tentatively ascribed to a [π(C≡CC_6H_4NH_2) → π~*(CNC)] LLCT excited-state origin. DFT and TDDFT computational studies have been performed to verify and elucidate the results of the electrochemical and photophysical studies.