The unsymmetrically substituted bi- and quaterthiophene derivatives were synthesized. The unsymmetrically substituted bithiophenes carrying the electron-withdrawing substituent X on one of the outer thiophene rings exhibited the maxima of absorption bands at the longer wavelengths than the symmetrically disubstituted bithiophene derivatives, while the unsymmetrical quaterthiophenes had such maxima at the shorter wavelengths than the corresponding symmetrical ones. The trend of bathochromic shift of the longest wavelength absorption bands due to the electron-withdrawing substituent X was more pronounced in case of bi- or quaterthiophenes bearing push–pull substituents. The unsymmetrical quaterthiophenes exhibited the greater third-order nonlinear optical (TNLO) properties than the corresponding bithiophenes, similarly to the case between the symmetrical bi- and quaterthiophenes. However, the TNLO properties of the unsymmetrical bi- and quaterthiophenes showed no dependence on the electron-withdrawing strength of the substituent X, unlike those of the symmetrical ones.

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1998 electron spectra, ESCA electron spectra, ESCA (organic substances) K 2515 -043Syntheses and Properties of Unsymmetrically Substituted Bi-and Quaterthiophenes.-In continuation of an earlier investigation concerning the molecular design for enhancement of the polarizable structural properties in this study unsymmetrical compounds of type (I) and (II) are synthesized. The electronic absorption spectral behaviors of these derivatives compared to symmetrical compounds is discussed. -(HIGUCHI, H.; URAKI, Y.; YOKOTA, H.; KOYAMA, H.; OJIMA, J.; WADA, T.; SASABE, H.; Bull.