THERMALLY IRREVERSIBLE PHOTOCHROMIC SYSTEMS - SUBSTITUENT EFFECT ON THE ABSORPTION WAVELENGTH OF 11,12-DICYANO-5A,5B-DIHYDRO-5A,5B-DIMETHYLBENZO(1,2-B-6,5-B')BIS[1]BENZOTHIOPHENE

Cyano- and halogen-substituted 1,2-bis(1-benzothiophen-3-yl)ethene derivatives were synthesized in an attempt to obtain compounds with sensitivity at longer wavelengths. Under UV irradiation, the derivatives underwent ring closure reactions to form the substituted 11,12-dicyano-5a,5b-dihydro-5a,5b-dimethylbenzo[1,2-b: 6,5-b']bis[1]benzothiophenes. Among cyano-substituted compounds, the 3,8-dicyano derivative showed an absorption maximum at the longest wavelength, 530 nm, which is 23 nm longer than the maximum of the unsubstituted compound. The absorption maximum of the 3,8-difluoro derivative, on the other hand, was 28 nm shorter than the maximum of the 2,9-difluoro derivative. Although the absorption maximum shift of the calculated values (MO INDO/S) by cyano substitution agreed well with the observed maxima, the calculation hardly reproduced the shift by halogen substitution.