Sung-Yu Ku

Electroluminescence based on thermally activated delayed fluorescence generated by a spirobifluorene donor-acceptor structure

An organic light emitting diode based on thermally activated delayed fluorescence (TADF) has been produced using a spirobifluorene derivative (Spiro-CN) having the donor-acceptor moieties as an emitter.

Surface patterning with fluorescent molecules using click chemistry directed by scanning electrochemical microscopy.

Scanning electrochemical microscopy (SECM)-based surface patterning can be achieved to form useful μm size structures for various kinds of applications. Here we report a novel SECM-based surface patterning of fluorescent molecules onto a solid substrate by forming covalent bonds through a click chemistry reaction. Patterned images can be observed by their fluorescence and we observed the formation of Liesegang rings in the diffusion−reaction system.

Electrochemical behavior and electrogenerated chemiluminescence of star-shaped D-A compounds with a 1,3,5-triazine core and substituted fluorene arms.

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.

Green electrogenerated chemiluminescence of highly fluorescent benzothiadiazole and fluorene derivatives.

A group of highly fluorescent 2,1,3-benzothiadiazole derivatives (BH0-BH3), including two fluorene derivatives (AB2 and C01) were synthesized and characterized. The electrochemical, spectroscopic, and electrogenerated chemiluminescence (ECL) properties of the compounds were determined. Benzothiadiazole derivatives BH1, BH2, and BH3 show reversible oxidation and reduction waves and produce strong green ECL in nonaqueous solutions. This ECL could be seen by the naked eye, even in a well lit room. The fluorene derivatives, C01 and AB2, also produce bright, easily observable ECL. Since the ECL spectra are at essentially the same wavelengths as the photoluminescence (PL) spectra, and the energies of the electron transfer reactions are greater than the singlet state energies, we propose direct formation of the excited singlet state during ion annihilation. BH0, which shows a quasi-reversible oxidation wave, only produced weak ECL via direct annihilation but gave strong ECL with benzoyl peroxide (BPO) as a coreactant. The ECL quantum efficiencies of the series, compared to that of 9,10-diphenylanthrace, was estimated to range from 0.05 to 7%. This series shows rare green photoluminescence (lambda(PL) = 490-556 nm) with a high PL quantum efficiency in solution (Phi = 5 to 90%).

High-luminescence non-doped green OLEDs based on a 9,9-diarylfluorene-terminated 2,1,3-benzothiadiazole derivative

We have prepared a highly efficient non-doped green organic light-emitting diode (OLED) incorporating a novel 9,9-diarylfluorene-terminated 2,1,3-benzothiadiazole green emitter (DFBTA), which exhibits an excellent solid state photoluminescence quantum yield (81%), and new triaryldiamines (DPAInT2, DPAInF) with high hole mobility derived from rigid and coplanar cores. The optimal device: ITO/DPAInT2/DPAInF/TCTA/DFBTA/Alq3/LiF/Al displayed impressive device characteristics, including a maximum external quantum efficiency (ηext) of 3.7% (12.9 cd A−1) and a maximum brightness at 168 000 cd m−2.

Electrochemistry and electrogenerated chemiluminescence of a spirobifluorene-based donor (triphenylamine)-acceptor (2,1,3-benzothiadiazole) molecule and its organic nanoparticles.

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.

An ambipolar host material provides highly efficient saturated red PhOLEDs possessing simple device structures

A highly efficient red electrophosphorescent device exhibited saturated red emission and an impressive external quantum efficiency [eta(ext) = 10.8% (ph/el)] with simple device configuration of doping an iridium complex (Mpq(2)Iracac) into a novel ambipolar spiro-configured donor-acceptor host material (D2ACN) has been developed.

Efficient and Stable Blue Electrogenerated Chemiluminescence of Fluorene‐Substituted Aromatic Hydrocarbons

Tailored molecular structure is the key to tune the electronicand spectroscopic properties of a molecule. This is always agoalinelectrogeneratedchemiluminescence(ECL),thatis,tohave a material with high photoluminescence (PL) quantumyield and stable, long-lived radical ions in solution uponoxidation and reduction. Among various ECL active materi-als, polyaromatic hydrocarbons (PAHs) were the earliestsubjects of ECL studies,

Spiro-Configured Bipolar Host Materials for Highly Efficient Electrophosphorescent Devices

In this study, we synthesized and characterized a series of spirobifluorene-based bipolar compounds (D2 ACN, DNPACN, DNTACN, and DCzACN) in which a dicyano-substituted biphenyl branch, linked orthogonally to a donor biphenyl branch bearing various diarylamines, acted as an acceptor unit allowing fine-tuning of the morphological stability, triplet energy, bipolar transport behavior, and the HOMO and LUMO energy levels. The promising physical properties of these new compounds, together with their ability to transport electrons and holes with balanced mobilities, made them suitable for use as host materials in highly efficient phosphorescent organic light-emitting diodes (PhOLEDs) with green iridium-based- or red osmium-based phosphors as the emitting layer (EML). We adopted a multilayer structure to efficiently confine holes and electrons within the EML, thus preventing exciton diffusion and improving device efficiency. The device incorporating D2 ACN doped with the red emitter [Os(bpftz)(2)(PPhMe(2))(2)] (bpftz=3-(trifluoromethyl)-5-(4-tert-butylpyridyl)-1,2,4-triazolate) gave a saturated red electrophosphorescence with CIE coordinates of (0.65, 0.35) and remarkably high efficiencies of 20.3 % (21 cd A(-1)) and 13.5 Lm W(-1) at a practical brightness of 1000 cd m(-2).