Helix Magic. Thermo-Driven Chiroptical Switching and Screw-Sense Inversion of Flexible Rod Helical Polysilylenes

Abstract

An ideal optically active helical chromophoric polymer comprising a flexible rodlike silicon main chain and enantiopure alkyl side chains, poly{(S)-3,7-dimethyloctyl-3-methylbutylsilylene}, underwent a thermodriven helix-helix transition at -20 °C in isooctane. The transition characteristics, including transition temperature, transition width, the population of right-and left-handed helical motifs, global shape, and screwpitch, were to be characterized quantitatively by spectroscopically analyzing circular dichroism (CD) and UV absorption characteristics. This is based on the unique property of the rodlike polymer in which the CD band completely matches the corresponding UV band profile at all temperatures. Moreover, fine controlling the contents and chirality of an additional chiral silylene unit incorporated in the copolymers allows free manipulation of the transition temperature in the range from -64 to +79 °C. Molecular mechanics calculation showed remarkable differences in the potential energy curve of the main chain torsion angle between flexible and rigid rodlike polysilylenes. These results and knowledge gained should assist in designing and controlling new types of helix-helix transition polymers directed to diverse screw-sense related properties and applications.

Optically Active Polysilylenes: State-of-the-Art Chiroptical Polymers

“…[79] The polysilylene gives an intense, narrow UV absorption band, completely matching the corresponding CD and FL band mirror image profiles, similar to the rigid rod-like helical polysilylenes described above. The occurrence of the P-M transition is easily detectable spectroscopically as an inversion of the CD band profile.…”

“…Recently, we found that certain poly(dialkylsilylene) homopolymers and copolymers [79] and poly(diarylsilylene) copolymer [78] undergo a thermo-driven P-M transition in solution by modification of their composition and side chains. This section highlights the most ideal poly-(dialkylsilylene)s suitable for quantitatively discussing thermo-responsive P-M transition characteristics.…”

Intramolecular Versus Intermolecular Induction of Helical Handedness in Pyridinedicarboxamide Oligomers

“…For instance, a right-handed bias induced in a helical polymer by a group of given chirality may be converted to a lefthanded bias by changing the polarity of the solvent or the temperature, [10][11][12][13][14] or even by more specific methods such as the binding of nonchiral guest molecules [15] or by irradiation with unpolarized [16][17][18][19] or circularly polarized light. [20,21] Consequently, a small change in the environment of the helical chain may give rise to a large chiroptical signal inversion, a feature that may be of use in some optical devices.…”

Helical, Chiral Polyisocyanides Bearing Ferrocenyl Groups as Pendants: Synthesis and Properties

“…Known responsive polymers, such as polyisocyanates, [7] polypeptides, [8] polymethacrylates, [9] polysilanes [10] and polyacetylenes, [11] are sensitive to light irradiation, thermal treatment, and chemical interaction, whereas there are no responsive polymers to date whose conformation can be controlled by electrical stimuli. Helical, chiral poly(ferrocenyl polyisocyanide)s may be prepared by the polymerization of chiral ferrocenyl isocyanides with initiator 1.…”