Abstract
A series of C <sub>2</sub> -symmetric, 10,11-disubstituted dibenzosuberane (DBS)-based helicenes 6-ac with a common 7-bromo-α-tetralin-based bottom fragment were synthesized. Their absolute stereochemistry was determined to be 10R,11R,P after reductive desulfurization of the corresponding (10R,11R,1?S)-episulfides with complete stereospecificity. Photoisomerization of the diastereomerically pure (P)-6-c in hexane led to virtually exclusive formation of the opposite M-form diastereomer (P/M?, <1:>99) at 290nm. The preferential return of (M?)-6-c to (P)-6-c was also achieved with high selectivity (P/M?, 90:10) at 330nm. Molecular simulations of (P)-6-c and (M?)-6-c with both DBS conformations suggest that the selectivities of photoswitching are controlled by the conformation of the top DBS template as evidenced by their <sup>1</sup> HNMR spectra. Doping 6-c into a nematic liquid crystal (E7) led to a cholesteric mesophase with modulated pitches, reversible helical senses, and with a switch memory of ternary logic. © 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.