Electrochiroptical systems based on biphenyl-2,2′-diyl-type dicationic dyes:: strong chiroptical signals through the transmission of point chirality to axial chirality

Huge CD amplitude (A = +538) was attained by diastereomeric preference (50% de) for the title dication with two bis[4(R)-sec-butoxyphenyl]methylium units in benzene at 23 degrees C. Intramolecular pi-pi stacking is the origin for effective transmission of point chirality to axial chirality to attain the chiroptical enhancement of 400-times. Thanks to the strong CD signaling, chiroptical changes upon electrolysis could be readily detected, thus realizing a new class of clectrochiroptical response systems. Chiroptical properties could also be modified by solvent polarity. (C) 2007 Elsevier Ltd. All rights reserved.