Synthesis, Electrochemistry, and Electrogenerated Chemiluminescence of Azide-BTA, a DAAD Species with Benzothiadiazole and <italic>N</italic>,<italic>N</italic>-Diphenylaniline, and Its Nanoparticles

We report the synthesis, electrochemical and photophysical characterization, and electrogenerated chemiluminescence (ECL) of a fluorescent molecule (Azide-BTA) and its NPs. Azide-BTA is a C2-symmetric donor acceptor (DA) compound, consisting of two 2,1,3-benzothiadiazole groups as the acceptors and triphenylamine as the donors bridged by a fluorene moiety (Scheme 1). The compound is a D A π A D molecule, which shows reversibility upon electrochemical oxidation and reduction and intense red fluorescence. We also fabricated stable organic nanoparticles (NPs) of Azide-BTA in an aqueous solution using a reprecipitation method and characterized their behavior in an aqueous solution. Metal and inorganic semiconductor NPs have been extensively investigated and show new physical phenomena, such as quantum confinement or finite size effects, distinct from the bulk materials. In contrast to the extensive research that has been done on metal and inorganic semiconductor NPs, the study of organic NPs is still at an early stage. Organic NPs are of interest because of their diverse structures, the flexibility and ease in their synthesis, and a binding affinity that can be tailored toward various materials. Organic NPs can be prepared in aqueous solution by solvent deposition in a vacuum chamber, laser ablation, sol gel phase transitions, and reprecipitation methods. The main challenge is to control the NP size and shape and to understand how these affect the optical and other properties. A large size (hence small diffusion coefficient) and low concentration are obstacles in electrochemical measurements of organic NPs since the observed currents are small. ECL has the advantage of high sensitivity and low background, so that it is possible to see an ECL signal as a function of potential, even when an electrochemical signal cannot be detected, and use this to obtain information about potentials for oxidation and reduction. It is also very sensitive as an analytical method and has been used to investigate organic molecules and several semiconductor NPs. Few ECL studies of organic NPs, e.g., 9,10-diphenylanthracene (DPA) and rubrene and spiro-BTA, have been reported. We found Azide-BTA NPs to be well dispersed and spherical with relatively small diameters (<20 nm)