Synthesis, Electrochemistry, and Electrogenerated Chemiluminescence of Azide-BTA, a D–A−π–A–D Species with Benzothiadiazole and N,N-Diphenylaniline, and Its Nanoparticles

Abstract

We report the synthesis, electrochemistry, spectroscopy, and electrogenerated chemiluminescence (ECL) of a donor (D)–acceptor (A) molecule of form D–A−π–A–D, 4,4′-(7,7′-(9,9-bis(6-azidohexyl)-9H-fluorene-2,7-diyl)bis(benzo[c][1,2,5]thiadiazole7,4-diyl))bis(N,N-diphenylaniline) (Azide-BTA), and its organic nanoparticles (NPs). Azide-BTA consists of two 2,1,3-benzothiadiazole (A) and triphenylamine (D) groups at the ends bridged by a fluorene (π) moiety. Cyclic voltammetry (CV) of Azide-BTA showed a single reversible reduction wave (Eored = −1.48 V vs SCE) and two reversible oxidation waves (Eo1,ox = 0.92 V, Eo2,ox = 1.34 V vs SCE). The first oxidation and reduction waves were assigned two reversible, closely spaced one-electron transfers. Azide-BTA exhibited a large solvatochromic effect in the emission ranging from yellow (580 nm) to red (633 nm). The ECL spectrum resulting from the annihilation reaction showed a bright and single peak with a maximum at 652 nm in mixed solvent of acetonitrile and benzene (MeCN/Bz). Using a reprecipitation method, we prepared well-dispersed and spherical organic NPs of Azide-BTA in an aqueous solution. The size of the NPs was controlled by the preparation conditions, i.e., concentration of Azide-BTA in THF, water temperature, stirring rate, and method of dropping into water. The smallest and most stable size of the NPs was 16 ± 6 nm as analyzed by TEM. Those organic NPs showed stable and moderate intensity in annihilation ECL emission in an aqueous solution. With a coreactant, such as peroxydisulfate, an ECL spectrum was obtained that showed a single broader peak relative to that produced by annihilation from dissolved Azide-BTA molecules.