Yu Miyagi

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).

Synthesis of platinum-containing poly(phenyleneethynylene)s having various chromophores: aggregation and optical properties

The Sonogashira–Hagihara coupling polymerization of platinum-containing m,m-phenylene and p,p-phenylene-linked diethynyl monomers m,m-1 and p,p-1 with 1,4-dibromobenzene 2a, 1,4-dibromonaphthalene 2b and 9,10-dibromoanthracene 2c was carried out to obtain the corresponding platinum-containing polymers [poly(m,m-1-2a)–poly(m,m-1-2c)] and [poly(p,p-1-2a)–poly(p,p-1-2c)] with Mns ranging from 4,300 to 28 000 in 24%-quantitative yields. The UV-vis absorption and emission properties of the formed polymers were measured in various solvents to examine the solvent effect on the optical properties. These polymers emitted fluorescence at 400–600 nm with 3.4–18.0% quantum yields in THF, CHCl3 and CH2Cl2. The fluorescence intensities of the polymers remarkably decreased upon raising the MeOH concentration in THF/MeOH mixtures, accompanying the formation of aggregates.

Effect of phosphine ligand on the optical absorption/emission properties of platinum-containing conjugated polymers

The Sonogashira–Hagihara coupling polymerization of a D-hydroxyphenylglycine-derived diiodoarylene monomer and platinum-containing diethynylphenylene monomers with various substituents, HCC–C6H4–CC–Pt(PR3)2–CC–C6H4–CCH, 1: R = C4H9, 2: R = C8H17, 3: R = cyclohexyl, 4: R = phenyl, and 5: R = 4-methoxyphenyl, gave the corresponding polymers 1′–5′ with number-average molecular weights of 4600–22 000. The polymers were soluble in CHCl3, CH2Cl2, THF and DMF. CD/UV–vis spectroscopic analysis and dynamic light scattering measurements revealed that 1′–5′ formed chirally regulated unimolecular structures in THF/toluene mixtures, while formed chiral aggregates in THF/MeOH mixtures. The conjugation of the polymer main chain was longer for monomers with aryl groups bonded to P compared to monomers with alkyl groups bonded to P. The relationship between the HOMO–LUMO gaps and phosphine ligands was reasonably explained by DFT calculations. The polymers exhibited photoluminescence with quantum yields ranging from 0.003% to 0.9%. The photoluminescence intensity was controlled by changing the phosphine substituents. The thermal stability of the polymers increased and the refractive index decreased as the alkyl chain length of the phosphine ligand was increased.