Molecular properties of helical polysilylenes in solution

Synchronization in Non-Mirror-Symmetrical Chirogenesis: Non-Helical π–Conjugated Polymers with Helical Polysilane Copolymers in Co-Colloids

A curious question is whether two types of chiroptical amplifications, called sergeants-and-soldiers (Ser-Sol) and majority-rule (Maj) effects, between non-charged helical copolymers and non-charged, non-helical homopolymers occur when copolymer encounter homopolymer in co-colloids. To address these topics, the present study chose (i) two helical polysilane copolymers (HCPSs) carrying (S)- or (R)-2-methylbutyl with isobutyl groups as chiral/achiral co-pendants (type I) and (S)- and (R)-2-methylbutyl groups as chiral/chiral co-pendants (type II) and (ii) two blue luminescent π-conjugated polymers, poly[(dioctylfluorene)-alt-(trans-vinylene)] (PFV8) and poly(dioctylfluorene) (PF8). Analyses of circular dichroism (CD) and circularly polarized luminescence (CPL) spectral datasets of the co-colloids indicated noticeable, chiroptical inversion in the Ser-Sol effect of PFV8/PF8 with type I HCPS. PF8 with type IIHCPS showed the anomalous Maj rule with chiroptical inversion though PFV8 with type IIHCPS was the normal Maj effect. The noticeable non-mirror-symmetric CD-and-CPL characteristics and marked differences in hydrodynamic sizes of these colloids were assumed to originate from non-mirror-symmetrical main-chain stiffness of HCPSs in dilute toluene solution. The present chirality/helicity transfer experiments alongside of previous/recent publications reported by other workers and us allowed to raise the fundamental question; is mirror symmetry on macroscopic levels in the ground and photoexcited states rigorously conserved?

Helical Assemblies of One-Dimensional Supramolecular Polymers Composed of Helical Macromolecules: Generation of Circularly Polarized Light Using an Infinitesimal Chiral Source

We report the synthesis of one-dimensional supramolecular polymers composed of one-handed helical macromolecules bearing fluorescent pendant groups and the generation of circularly polarized light on the basis of hierarchical chiral amplification starting from a tiny amount of chiral substituent. Copolymerization of benzo[1,2-b:4,5-b']dithiophene-appended achiral/chiral isocyanides (99:1, mol/mol) with a solid-state photoluminescence feature afforded submicrometer supramolecular fibers, in which almost perfect single-handed helical polyisocyanides were noncovalently connected end to end. The resulting helical supramolecular polymers were further helically assembled to form a cholesteric liquid crystal film with an intense circularly polarized luminescence (CPL) signal. Surprisingly, the supramolecular system containing only 0.01 mol % of the chiral monomer unit also emitted the observable circularly polarized light owing to multiple chiral amplification from an infinitesimal point chirality to helical chirality and then to supramolecular chirality. Furthermore, chiral information was efficiently transferred from the helically assembled supramolecular system containing 1 mol % of the chiral unit to achiral dye molecules blended in the film, allowing full-color tunable induced CPL with luminescence dissymmetry factors greater than 1.0 × 10^-2. This unprecedentedly strong chiral amplification enables the creation of helical supramolecular polymers and chirally assembled systems with various chiral functions based solely on an infinitesimal chiral source.

Synthesis and helical structures of poly(ω-alkynamide)s having chiral side chains: effect of solvent on their screw-sense inversion

New ω-alkynamides, (S)-HC≡CCH2CONHCH2CH(CH3)CH2CH3 (1) and (S)-HC≡CCH2CH2CONHCH(CH3)CH2CH2CH2CH2CH3 (2) were synthesized and polymerized with a rhodium catalyst in CHCl3 to obtain cis-stereoregular poly(ω-alkynamide)s (poly(1) and poly(2)). Polarimetric, CD, and IR spectroscopic studies revealed that in solution the polymers adopted predominantly one-handed helical structures stabilized by intramolecular hydrogen bonds between the pendent amide groups. This behavior was similar to that of the corresponding poly(N-alkynylamide) counterparts (poly(3) and poly(4)) reported previously, whereas the helical senses were opposite to each other. The helical structures of the poly(ω-alkynamide)s were stable upon heating similar to those of the poly(N-alkynylamide)s, but the solvent response was completely different. An increase in MeOH content in CHCl3/MeOH resulted in inversion of the predominant screw-sense for poly(1) and poly(2). Conversely, poly(3) was transformed into a random coil, and poly(4) maintained the predominant screw-sense irrespective of MeOH content. The solvent dependence of predominant screw-sense for poly(1) and poly(2) was reasonably explained by molecular orbital studies using the conductor-like screening model (COSMO).

Novel PPV/mesoporous organosilica composites: influence of the host chirality on a conjugated polymer guest

The conjugated polymer poly(p-phenylenevinylene) (PPV) was polymerized in the pores of chiral nematic mesoporous organosilica to give a composite film showing the strong characteristic fluorescence of PPV as well as the iridescence due to the photonic band gap of the host material. Detailed circular dichroism (CD) studies reveal a chiral structure of the polymer within the pores. These new fluorescent materials undergo fluorescence quenching upon exposure to electron deficient aromatics such as 2,4,6-trinitrotoluene (TNT), indicating that they may be useful for developing chemical sensors.

Polymerization of substituted acetylenes and features of the formed polymers

This review summarizes the recent advances of substituted polyacetylene chemistry, including new polymerization catalysts and the properties and functions of the polymers.

Polarized optical spectroscopy applied to investigate two poly(phenylene-vinylene) polymers with different side chain structures

Two related poly(phenylene-vinylene) (PPV) light-emitting polymers have been investigated by means of polarized optical spectroscopy. The purpose of the investigation was to investigate the nature of the interactions in thin films and to examine what impact the difference in side chain structure and molecular weight in poly(2'-methoxy-5-2-ethyl-hexoxy)-1,4-phenylene vinylene (MEH-PPV) and poly(2-(3',7'-dimethyloctyloxy)-5-methoxy-1,4-phenylene-vinylene) (OC1C10-PPV) has on the electronic and optical properties of the two polymers. Aligning the polymers by dispersing them in anisotropic solvents and stretched films shows that the side chains have an impact on the relative orientations of the transition dipole moments. In anisotropic solvents the linear dichroism is larger for MEH-PPV than for the related polymer OC1C10-PPV, while in stretched films the opposite situation prevails. A lower polarization of the luminescence from OC1C10-PPV, relative to MEH-PPV, was also obtained independent of alignment medium used. The data therefore suggest that while mechanical stretching may align the OC1C10-PPV to a greater degree, the emitting species is distinct from the absorbing species. The circular dichroism (CD) spectra of both polymers undergo dramatic changes when the liquid phase and the solid state (film) are compared. The solution CD spectra shows no evidence of interchain interactions; instead the spectra of both systems indicate a helical conformation of the polymers. The CD spectra of films are dramatically different with the strong Cotton effect being observed. This points to the formation of an aggregate in the film, with an associated ground state interaction, an interchain species such as a physical dimer, or a more complex higher aggregate.

Control of Helix Sense by Composition of Chiral-Achiral Copolymers ofN-Propargylbenzamides

N-Propargylbenzamides 1-7 were polymerized with (nbd)Rh(+)[eta(6)-C(6)H(5)B(-)(C(6)H(5))(3)] to afford polymers with moderate molecular weights (M(n) = 26,000-51,000) in good yields. The (1)H NMR spectra demonstrated that the polymers have fairly stereoregular structures (81-88 % cis). The optically active polymers, poly(1) and poly(2), were proven by their intense CD signals and large optical rotations to adopt a stable helical conformation with an excess of one-handed screw sense when heated in CHCl(3) or toluene. The sign of Cotton effect could be controlled by varying the content in the copolymers of either chiral bulky 1 and achiral nonbulky 3, or chiral nonbulky 2 and achiral bulky 7. The smaller the pendant group in the copolymerization of achiral monomers with 1, the more easily did the preferential helical sense change with the copolymer composition. However, the copolymers of chiral nonbulky 2 and achiral nonbulky 3 did not change the helical sense, irrespective of the composition. The free energy differences between the plus and minus helical states, as well as the excess free energy of the helix reversal, of those chiral-achiral random copolymers were estimated by applying a modified Ising model.