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We report the synthesis, electrochemistry, and electrogenerated chemiluminescence of a series of star-shaped donor-acceptor (D-A) molecules. The star-shaped molecules consist of an electron-deficient 1,3,5-triazine core with three fluorene arms substituted with diarylamino (TAM1-TAM3) or carbazolyl (TAM4) electron donors. Cyclic voltammetry of TAM1-TAM3 shows that the reduction consists of one wave of single electron transfer to the core, while the oxidation exhibits a single peak of three sequential electron-transfer processes, with the formation of a trication. The carbazole-containing molecule TAM4 after oxidation undergoes a subsequent rapid chemical reaction to produce a dimer (via the overall coupling of two radical cations with the loss of two protons). The dimer electrooxidizes more easily than the monomer of TAM4. With continuous cycling on the oxidation side, a conductive polymer film is formed on the surface of the working electrode. Because of the presence of the acceptor (triazine) center and strong donors in the arms (diarylamine or carbazole), TAM1-TAM3 exhibit large solvatochromic effects with emissions ranging from deep blue (428 nm) to orange-red (575 nm) depending on the solvent polarity. These star-shaped molecules show high PL quantum yields of 0.70-0.81. The electrogenerated chemiluminescence (ECL) of TAM1-TAM3 in nonaqueous solutions showed strong ECL that could be seen with the naked eye in a well-lit room. Because the enthalpy of annihilation is higher than the energy required for formation of the singlet excited state, the ECL emission is believed to be generated via S-route annihilation. However, TAM4 shows weak annihilation ECL because of the production of polymer film on the electrode surface during oxidation cycles. However, by limiting the potential region only to the reduction side and using benzoyl peroxide (BPO) as a coreactant, strong ECL of TAM4 can be obtained.

A new D-A-π-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 (Φ(PL) = 0.51) in a solid film. A cyclic voltammogram of Spiro-BTA in 1:2 MeCN:benzene/0.1 M Bu(4)NPF(6) 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 ∼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 (∼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 (Φ(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.

We report the preparation, characterization, and electrogenerated chemiluminescence (ECL) of rubrene nanoparticles (NPs) and 9,10-diphenylanthracene (DPA) nanorods. The organic NPs were prepared in an aqueous phase using a simple reprecipitation method, i.e., injecting a solution of the hydrocarbon in an organic solvent into water. The resulting NPs can be collected and redispersed to form stable colloidal solutions in water. Rubrene forms spherical nanoparticles (NPs) (diameter ∼50 nm), while DPA initially forms nanorods with an average size of ∼500 nm in length and ∼50 nm in diameter. DPA nanorods grew gradually with time into wires with diameters of ∼1 μm and lengths of ∼10 μm. ECL emission from these NPs was observed upon electrochemical oxidation in aqueous solutions containing different co-reactants, such as tri-n-propylamine for rubrene and an oxalate ion for DPA NPs. The ECL intensity from rubrene NPs was significantly higher than that from DPA NPs because of the smaller size, and thus there is a higher diffusion coefficient for rubrene as compared to that of DPA NPs.

The single crystalline nanobelts were successfully fabricated with an ionic compound by a simple reprecipitation method. The compound used is the water-insoluble derivative of tris(bipyridine) Ru(II), [Ru(bpy)2(4,4'-(CH3(CH2)14COO)2-bpy)](ClO4)2. The prepared nanobelts show an enhanced fluorescence emission and relatively strong electrogenerated chemiluminescence (ECL), that have potential analytical applications. More interesting, ECL of a single nanobelt deposited on an ultramicroelectrode was observed. The observation of ECL in such nanostructures leads to the development of a new class of ECL systems that may prove useful for a variety of purposes.