Sang Hae Lee

Nonlinear optical and two-photon absorption properties of 1,3,5-tricyano-2,4,6-tris(styryl)benzene-containing octupolar oligomers

Octupolar oligomers containing 2-12 molecules of 1,3,5-tricyano-2,4,6-tris(styryl)benzene derivatives have been synthesized and their nonlinear optical and two-photon absorption (TPA) properties were determined. The beta(0) values are in the range of (85-1219) x 10(-30) esu and increase monotonically with the increasing number of the octupolar units within the molecule. The two-photon-induced fluorescence excitation spectra are quite similar to the single-photon absorption spectra except that the wavelength is doubled, indicating that the one- and two-photon allowed excited states are the same. The peak TPA cross-section values (delta(max)) measured with nanosecond pulses by the two-photon-induced fluorescence method are in the range (3010-62, 930) x 10(-50) cm(4)s photon(-1). The delta(max) increases as the number of the octupolar units in the molecules increases. A linear relationship is observed between delta(max) and beta, and this delta-beta relationship serves as a useful design strategy for the synthesis of novel octupolar oligomers and polymers with large TPA and beta.

Novel azo octupoles with large first hyperpolarizabilities

Novel two-dimensional octupoles containing azo groups and their oligomers have been synthesized and their first hyperpolarizabilities were determined. The λmax and β(0) values of azo octupoles are nearly the same regardless of the nature of the bridge or the conjugation length. On the other hand, 1,3,5-tricyano-2,4,6-tris[4-(p-diethylaminostyryl)styryl]benzene has a larger β(0) value than the corresponding azo analogue probably due to the more efficient conjugation ability of CC compared with the NN bond. The β(0)/MW of the octupoles are larger than the corresponding dipoles, whereas those of the azo octupoles are comparable to the latter. Also, retention of monomeric β(0) is observed in the octupolar oligomers.

Synthesis and two-photon absorption property of phenylacetylene macrocycles

The first synthesis of phenylacetylene macrocycle with large two-photon absorption cross section is reported.

Molecular hyperpolarizabilities of barbituric acid and cyclobutene-1,2-dione derivatives. Electronic and steric effects

A series of merocyamne dyes containing various donors and barbituric acid and cyclobutene-1,2-dione moieties as the acceptors have been synthesized and their first-order hyperpolarizabilities β were determined. The β values of barbituric acid derivatives increase as the strength of the donor is increased from 4-dimethylaminophenyl to trimethylindolinyl to benzothiazolinyl, apparently due to the gradual decrease in the bond length alternation (BLA) from a large positive value to an optimum one by a stronger donor. In contrast, the β values for the cyclobutene-1,2-dione derivatives decrease with the same variation of the donors even though the cyclobutene-1,2-dione is a poorer acceptor than the barbituric acid moiety. The results have been attributed to the electron-donating ability of the donors and the increased distortion of the chromophores from planarity.

First Hyperpolarizabilities of Stilbenes Derivatives

Abstract Stilbene and heteroaromatic stilbene derivatives have been synthesized and their β values were determined. The result of HRS measurements indicates that the β(O) values are larger for the heteroaromatic stilbenes than the stilbenes. For stilbene derivatives, the β(O) increased as the acceptor strength was increased.