SYMPOSIUM AA Advances in Materials Theory and Modeling{Bridging Over Multiple-Length and Time Scales Chairs

Withdrawn. A MOLECULAR ORBITAL STUDY ON THE OPTICAL PROPERTIES OF FLUORESCENT DYES. Su-Jin Park, Seung-Hoon Choi, Dae-Yup Shin, Han-Yong Lee, Ho-Kyoon Jung, Corporate R&D Ctr, Samsung SDI Co. Ltd., Suwon, KOREA; Jung-Sik Kim, Jin-Kyu Lee, School of Chemistry and Molecular Engr, Seoul Natl Univ, Seoul, KOREA; Sung Soo Park, Seeyearl Sung, Kyoung Tai No, Computer Aided Molecular Design Research Ctr, SoongSil Univ, Seoul, KOREA. Nile Red (NR), uorescein and 4-(dicyanomethylene)-2-methyl-6-(pdimethylaminostyryl)-4H-pyran (DCM) are well-known uorescent laser dyes and their luminescent characteristics have been studied for the organic light emitting device (OLED) application. Even though a wealth of experimental and theoretical approaches on optical properties of these dyes is available, however, systematic studies on the substituents e ect of their derivatives have not been thoroughly investigated. We carried out some calculations and experiments to nd the simple and easy way to predict the substituent e ects on these dyes, in order to make e cient red luminescent dopant materials. Relationship between the molecular structure and optical properties were calculated by ab initio and semiempirical calculation methods such as DFT/AM1/PM3 and INDO/S for the geometry optimization and for the information of electronic transition, respectively. Since the result of these calculations was comparable with several experimental results, these semiempirical molecular orbital calculation methods could be used as a powerful prediction tool for optical properties of the luminescent molecules. It was also found that the absorption maximum and the oscillator strength of molecules strongly depended on the molecular dipole moment, especially for the molecules having both strong electron donor and acceptor groups. PREDICTION OF SOLVATOCHROMIC SHIFT OF FLUORESCENT DYES USING REGRESSION AND NEURAL NETWORK TECHNIQUES. Seung-Hoon Choi, Su-Jin Park, Dae-Yup Shin, Han-Yong Lee, Ho-Kyoon Jung Corporate R&D Center, Samsung SDI Co. Ltd., Suwon, KOREA; Seung Hee Lee, Jin-Kyu Lee, School of Chemistry and Molecular Engineering, Seoul National University, Seoul, KOREA; Sung Soo Park, Seeyearl Sung, Kyoung Tai No, Computer Aided Molecular Design Research Center, SoongSil University, Seoul, KOREA. In order to investigate the relationship between the solvatochromic shift and the intrinsic properties of uorescent dyes, a novel series of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4Hpyran(DCM) derivatives was studied by computer aided molecular design. Molecular orbital calculations such as AM1/PM3 and INDO(S) were used for the geometry optimization and for the information of electronic transition, respectively. SCRF calculation was also performed to consider the medium polarity with the virtual solvent having the dielectric constants from 1 to 80 with the interval of 10. Based on the calculated optical properties under various solvents, quantitative structure-property relationship study on solvatochromic shift was carried out using genetic algorithm and arti cial neural network technique. It was found that the variations of the polarity of medium induce the remarkable changes in absorption band positions and intensity. The absorption intensity (oscillator strength) as well as the position of absorption maxima seems to be strongly correlated with the molecular properties, such as dipole moment and energy band gap of DCM derivatives. From these calculated results, it is possible to guess how much the position of absorption maxima of uorescent dyes will shift as the function of solvent polarity. And these calculations could also provide some clues to understand the di erences between photoluminescence and electroluminescence due to the chemical environments around the luminescent molecules. COUPLED ATOMISTIC{MESOSCOPIC MODELLING OF POLYCRYSTALLINE PLASTICITY. F. Cleri and G. D'Agostino, ENEA, Divisione Materiali, Centro Ricerche Casaccia, Roma, ITALY; A. Satta and L. Colombo, INFM and Dipartimento di Fisica, Universita di Cagliari, Monserrato, ITALY. Modelling the complex interplay of phenomena contributing to plastic deformation in a polycrystalline microstructure is one of the most challenging subjects of materials science. Even discarding impurity e ects, voids and inclusions, still a number of possible processes are competing in the di erent ranges of temperature, external strain and strain rate. We present the latest results of our stochastic mesoscale model [1,2], which includes dislocation plasticity at di erent levels of sophistication and grain{boundary plasticity resulting from (di usion{mediated) grain sliding. The ultimate goal is to describe the crossover between dislocation{mediated and interface{mediated plasticity in a real microstructure, whose most spectacular evidence is the so{called inverse Hall{Petch e ect. The technical implementation of the model is also brie y discussed. Moreover, we describe how atomic{level simulations do represent an integral part of the mesoscopic modelling, both to supply the qualitative behavior of physical parameters and to identify the relative importance of the various microscopic events leading to microstructural evolution, some of which still to be addressed experimentally. [1] F. Cleri, Physica A282, 339 (2000). [2] F. Cleri and G. D'Agostino, MRS Fall Meeting 2000, Proceedings of the Symposium \In uences of Interface and Dislocation Behavior on Microstructure Evolution", in press. Work performed in the