How to achieve near unity fluorescence quantum yields on gold(I) benzothiadiazole-based derivatives

Abstract

TThe synthesis of three new gold(I) benzothiadiazole derivatives has been carried out by the reaction of 4-ethynyl-7-(4-nonylphenyl)benzo[c] [1,2,5]thiadiazole (L) with three different gold(I)-PR3 (PR3 = triethylphosphane (2), triphenylphosphane (3) and tri-1-naphthylphosphane (4)) sources and their light emitting properties thoroughly investigated. The new compounds display denoted luminescence properties with fluorescence quantum yields above 80% in all cases except for the complex containing the bulkiest PNaph3 phosphane. The resulting emission is mainly dominated by the organic 2,1,3-benzothiadiazole moiety (BTD) and can be modulated following different strategies. On one hand, the emission wavelength of these compounds in solution can be ca. 60 nm shifted varying the polarity of the solvents. Interestingly, quantum yields and lifetimes can be strongly increased by changing the environment conditions, from water:acetonitrile solutions to dispersion of the compounds within organic matrixes. In this way, we have been able to obtain near unity fluorescence quantum yields, with the highest values recorded for gold(I) BTD compounds. The effect of the solvents on the emission changes has been rationalized with the help of the Lippert-Mataga equation and the multiparametric Kamlet-Taft method to analyse the excited state polarity.