Shiwei Yin

Geometric and electronic structures of the boron-doped photocatalyst TiO2

Boron-doped anatase TiO2 has been shown to be a much more efficient and stable photocatalyst than the pristine TiO2. We employed the LDA-supercell approach to calculate the geometry and electronic structures of the doped systems, in order to reveal the microscopic mechanism of how photocatalytic efficiency is improved by boron doping. It is found that the boron atom tends to either replace an oxygen atom or sits in the interstitial position. It is highly unlikely for the boron atom to replace Ti. The density of states analysis shows that for oxygen-substituted doping the boron atom is strongly bonded to two oxygen atoms as well as to two Ti atoms, which results in new midgap states, and eventually the absorption edge is red-shifted and the photocatalytic efficiency is enhanced.

A Quantitative Structure−Property Relationship Study of the Glass Transition Temperature of OLED Materials

Organic light-emitting-diodes (OLED) materials possess great potential applications. Stability and efficiency are the two major factors to be improved toward commercialization, especially the thermal stability, because in the working device, the organic molecular materials can have high temperature. One of the most important factors, which influences the stability, is the glass transition temperature (T(g)). We employed a QSPR (quantitative structure-properties relationship) approach to establish a theoretical model to predict the glass transition temperatures of organic molecular materials. A six-parameter correlation with the squared correlation coefficient R(2) = 0.9270 and the average absolute error 8.5 K was developed for a diverse set of 73 OLED materials. All descriptors were derived solely from the chemical structures of the organic compounds. A satisfactory average absolute error of 17.9 K for a test set of 15 OLED materials makes the model very useful for the prediction of the unknown OLED materials.

Efficient blue electroluminescent device using tetra(β-naphthyl)silane as a hole-blocking material

We report an efficient blue light-emitting diode (LED) using N, N′-bis(1-naphthyl)-N, N′-diphenylbenzidine as an emitting layer and tetra(β-naphthyl)silane (TNS) as a hole-blocking layer (HBL). We find that the hole-blocking performance, thermal stability, and film-forming ability of TNS are improved over those of the prototypical hole-blocking material 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP). The device that used TNS as the HBL exhibits a narrower light emission and higher current efficiency (2.5cd∕A) as compared with the device containing BCP as the HBL. TNS should be promising as an excellent hole-blocking layer in LEDs.

THEORETICAL DESIGN OF LIGHT-EMITTING POLYMERS — SUBSTITUTION EFFECTS OF EXCITED STATE ORDERING OF POLYDIACETYLENE AND POLYACETYLENE

The excited states structure, essential in determining the light-emitting properties, in a correlated electron system behaves differently from the one-electron system. Previous investigations show that upon proper chemical substitution, the non-emissive polyacetylene (PA) can be designed to be strongly light-emitting materials. On the basis of the correlated quantum chemical calculations within the INDO/EOM-CCSD approach, we systematically studied both the pristine and substituted polydiacetylene (PDA) about the low-lying excited states orderings. PDA possesses high mobility, but it is non-emissive. We predict that it is impossible to cause PDA to be light-emitting. From these numerical results, we propose a simple and practical rule to design conjugated light-emitting polymers, which require only a molecular orbital calculation instead of sophisticated correlated calculations. This rule is derived from physical pictures of correlated electron model, and is found to be in agreement with the existing experiments for various substituted PA and poly(p-phenylenebutadiynylene) (PPPB).