Electrochemistry and Electrogenerated Chemiluminescence of a Spirobifluorene-Based Donor (Triphenylamine)-Acceptor (2,1,3-Benzothiadiazole) Molecule and Its Organic Nanoparticles

A new D-A-pi-A-D molecule (Spiro-BTA) containing two 2,1,3-benzothiadiazole (BTA) as the acceptor (A) and triphenylamine as the donor (D) bridged by a spirobifluorene moiety has been synthesized. The novel D-A molecule shows intense red emission (612 nm) with a high PL quantum yield (Phi(PL) = 0.51) in a solid film. A cyclic voltammogram of Spiro-BTA in 1:2 MeCN:benzene/0.1 M Bu4NPF6 shows two reversible oxidation waves and one reversible reduction wave. The first oxidation wave and reduction wave were assigned as two successive electron transfer peaks separated by similar to 50 mV related to the oxidation of the two noninteracting donors and the reduction of the two noninteracting acceptors, respectively. Electrogenerated chemiluminescence (ECL) of Spiro-BTA upon cyclic oxidation and reduction in MeCN:benzene 1:2 shows a very bright and stable red emission that could be seen in a well-lit room. Using a reprecipitation method, well-dispersed organic nanoparticles (NPs) of the Spiro-BTA were prepared in aqueous solution. The nanoparticles were analyzed by dynamic light scattering (DLS) and scanning electron microscopy (SEM), yielding a NP size (without surfactant) of 130 +/- 20 nm, while with surfactant, 100 +/- 20 nm. Bathochromic shifts of absorption spectra (similar to 16 +/- 2 nm), as compared to that of the dissolved Spiro-BTA in THF, were observed for both NPs in water and as a thin film. While blue shifts (14 +/- 2 nm) were observed for the photoluminescence (PL). The PL intensity of the Spiro-BTA nanoparticles was slightly enhanced (Phi(PL) of nanoparticles in water = 48%) over that of the dissolved Spiro-BTA in THF. The ECL of the organic Spiro-BTA nanoparticles in aqueous solution could be observed upon oxidation with tri-n-propylamine as a coreactant.