2,2′-(Dihexyl-2,2′-bithienylidene-5,5′-diylidene)bis(propanedinitrile)s (dihexylbithienoquinonoid derivatives), in which two 3-hexylthiophene moieties are connected with head-to-tail (HT) and tail-to-tail (TT) orientations, were synthesized. HT bithienoquinonoid was isolated in a single form together with a small amount of its bromo derivative, similarly to the case for the head-to-head (HH) orientational isomer. On the other hand, TT isomer exhibited a peculiar feature in solution, affording an equilibrium mixture of two geometrical isomers. Electronic and electrochemical properties of these bithienoquinonoids were studied and compared with those of HH isomer. The results proved that all these bithienoquinonoid compounds possess highly polarizable and electron-acceptable properties. HH bithienoquinonoid was reduced through one two-electron transfer process, while HT and TT isomers were reduced through two one-electron transfer processes via stable radical anions to the corresponding dianions.

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.

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.

Synthesis and Properties of Dihexylbithienoquinonoid Derivatives with Head-to-head, Head-to-tail, and Tail-to-tail Orientations.-The bithienoquinonoids (VI) and (X) with head-to-tail (HT) and tail-to-tail (TT) orientations, resp., are synthesized. The electronic and electrochemical properties of the bithienoquinonoids with HH, HT, and TT orientations and of their bromo derivatives are described, along with a peculiar feature of TT isomer (X) in solution. - (HIGUCHI, H.; YOSHIDA, S.; URAKI, Y.; OJIMA, J.; Bull. Chem. Soc. Jpn. 71 (1998) 9, 2229-2237 Dep. Chem., Fac. Sci., Toyama Univ., Gofuku, Toyama 930, Japan; EN)