Computing handedness: Quantized and superposed switch and dynamic memory of helical polysilylene

Two new conjugating helical polymers comprising a rodlike silicon backbone and enantiopure chiral pendants, poly{(R)-3,7-dimethyloctyl-(S)-3-methylpen tylsilyle} (PS.1) and its diastereomeric poly {(S)-3,7-dimethyloctyl-(S)-3- methylpentylsilylene} (PS-2), were prepared. Molecular mechanics calculatio ns of PS-1 and PS-2 model oligomers indicated a double well potential energ y curve corresponding to almost enantiomeric helices with dihedral angles o f 150-160 degrees (P-motif, global minimum) and 200-210 degrees (M-motif), regardless of their tacticity. Experimentally, it was found that PS-I in di lute isooctane revealed switchable ambidextrous helicity on application of a thermal energy bias. Although PS-1 featured three distinct switching regi ons, viz. "region 1, between -80 and -10 degreesC", "region 2, between -10 and +10 degreesC", and "region 3, between +10 OC and +80 degreesC", the swi tching properties were interpreted as the result of superposed P- and M-hel icities, undergoing dynamic pseudo-racemization or oscillation. Oscillating helicity in region 2 was roughly estimated to be about 13 cm(-1). The supe rposed helicity in region 2 was critical since it afforded molecular recogn ition ability with a dynamic memory function that was highly susceptible to solvent molecular topology and volume fraction. This could lead to potenti al as a molecular information processor to serve as a gauge of chemical pro perties. On the other hand, PS-2 could not switch its preferential screw-se nse in the range of -80 to +80 degreesC. This may be related to greater dif ferences the potential energy curve between P- and M-motifs.