Modulation of photoswitching profiles by 10,11-dialkoxymethyl substituents in c(2)-symmetric dibenzosuberane-based helicenes.
A series of C(2)-symmetric, 10,11-disubstituted dibenzosuberane (DBS)-based helicenes 6 a-c 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 290 nm. The preferential return of (M')-6 c to (P)-6 c was also achieved with high selectivity (P/M', 90:10) at 330 nm. 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 (1)H NMR 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.
Department of Chemistry, National Taiwan Normal University, No. 88, Sec. 4, Ding-Jou Road, Taipei, Taiwan, ROC.
Wen-Ching
WC
Chen
Po-Chiao
PC
Lin
Chien-Hsiang
CH
Chen
Chien-Tien
CT
Chen