Journal of the American Chemical Society, Vol.129, No.14, 4350-4365, 2007
A class of luminescent cyclometalated alkynylgold(III) complexes: Synthesis, characterization, and electrochemical, photophysical, and computational studies of [Au(CNC)(C C-R)] (CNC = kappa C-3,N,C bis-cyclometalated 2,6-diphenylpyridyl)
A new class of luminescent cyclometalated alkynylgold(III) complexes, [Au(RC boolean AND N(R')boolean AND CR)(CCR '')], i.e., [Au(C boolean AND N boolean AND C)(CCR '')] (HC boolean AND N boolean AND CH = 2,6-diphenylpyridine) R '' = C6H5 1, C6H4Cl-p 2, C6H4NO2-p 3, C6H4OCH3-p 4, C6H4NH2-p 5, C6H4C6H13-p 6, C6H13 7, [Au((BuC)-Bu-t boolean AND N boolean AND(CBu)-Bu-t)(CCC6H5)] 8 ((HBuC)-Bu-t boolean AND N boolean AND(CBuH)-Bu-t = 2,6-bis(4-tert-butylphenyl)pyridine), and [Au(C boolean AND NTol boolean AND C)(CCC6H4-C6H13-p)] 9 (HC boolean AND NTol boolean AND CH = 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 pi-pi* intraligand (IL) transition of the cyclometalated RC boolean AND N(R')boolean AND CR ligand with some mixing of a [pi(CCR '') -> pi*(RC boolean AND N(R')boolean AND 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 pi-pi* IL transition of the cyclometalated RC boolean AND N(R')boolean AND 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 [pi(CCC6H4NH2) -> pi*(C boolean AND N boolean AND C)] LLCT excited-state origin. DFT and TDDFT computational studies have been performed to verify and elucidate the results of the electrochemical and photophysical studies.