Thermoresponsive Helical Poly(phenylacetylene)s

Poly­(phenylacetylene) (PPA) bearing dendritic oligo­(ethylene glycol) (OEG) as pendants was synthesized, and its thermoresponsiveness and helical conformation were investigated. Despite the steric hindrance of the bulky pendants in the homopolymer PPA-OEG, the chirality could be efficiently transferred from pendant alanine moieties to PPA main chain through ester linkage. In order to examine the steric effect of pendants on chiral transformation, a model PPA homopolymer PPA-Boc which carries less bulky moieties was prepared for comparison. The chiroptical properties of these thermoresponsive PPAs were further investigated by varying temperature to examine the effects of their thermoresponsiveness. In addition, PPA copolymers PPA-BDY bearing OEG dendron and fluorescent boradiazaindacene (BDY) chromophore showed excellent thermoresponsive properties and interesting fluorescence enhancement at elevated temperatures. To investigate the rigidity effects of polymer backbone on the thermally induced fluorescence enhancement, a nonchiral polymer carrying the same pendants but with polymethacrylate as the backbone (PMA-OEG) was prepared. It was found that the chiroptical and fluorescence properties of these PPAs are dependent not only on their chemical structures but also on the thermoresponsiveness

Polymerization of Phenylacetylenes Using Rhodium Catalysts Coordinated by Norbornadiene Linked to a Phosphino or Amino Group

The novel rhodium (Rh) catalysts [{nbd-(CH₂)₄-X}­RhR] (<b>1</b>, X = PPh₂, R = Cl; <b>2</b>, X = NPh₂, R = Cl; <b>3</b>, X = PPh₂, R = triphenylvinyl; nbd = 2,5-norbornadiene) were synthesized, and their catalytic activities were examined for the polymerization of phenylacetylene (PA) and its derivatives. Rh-103 NMR spectroscopy together with DFT calculations (B3LYP/6-31G*-LANL2DZ) indicated that catalyst <b>1</b> exists in a mononuclear 16-electron state, while <b>2</b> exists in dinuclear states. Catalyst <b>1</b> converted PA less than 1% in the absence of triethylamine (Et₃N). Addition of Et₃N and extension of the polymerization time enhanced the monomer conversion. On the other hand, catalysts <b>2</b> and <b>3</b> quantitatively converted PA in the absence of Et₃N to afford the polymer in good yields. Catalyst <b>3</b> achieved two-stage polymerization of PA

Polymerization of Phenylacetylenes Using Rhodium Catalysts Coordinated by Norbornadiene Linked to a Phosphino or Amino Group

The novel rhodium (Rh) catalysts [{nbd-(CH₂)₄-X}­RhR] (<b>1</b>, X = PPh₂, R = Cl; <b>2</b>, X = NPh₂, R = Cl; <b>3</b>, X = PPh₂, R = triphenylvinyl; nbd = 2,5-norbornadiene) were synthesized, and their catalytic activities were examined for the polymerization of phenylacetylene (PA) and its derivatives. Rh-103 NMR spectroscopy together with DFT calculations (B3LYP/6-31G*-LANL2DZ) indicated that catalyst <b>1</b> exists in a mononuclear 16-electron state, while <b>2</b> exists in dinuclear states. Catalyst <b>1</b> converted PA less than 1% in the absence of triethylamine (Et₃N). Addition of Et₃N and extension of the polymerization time enhanced the monomer conversion. On the other hand, catalysts <b>2</b> and <b>3</b> quantitatively converted PA in the absence of Et₃N to afford the polymer in good yields. Catalyst <b>3</b> achieved two-stage polymerization of PA

OEGylated Cyclodextrins Responsive to Temperature, Redox, and Metal Ions

The present work provides a versatile access for “smart” cyclodextrins (CDs) that are responsive to temperature, redox, and metal ions. These CDs are modified with oligoethylene glycols through thiol–ene click chemistry, which are inherently thermoresponsive in aqueous solutions. At the same time, their thermoresponsiveness is tunable through oxidation or metal ion chelation of thioether moieties. Significantly, these stimuli-responsive CDs retained strong inclusion abilities to guest dyes, and the inclusion complexation can be tuned by thermally induced phase transitions, oxidation, as well as metal chelation. The stimuli-responsive complexation with dyes allows to fabricate colorimetric/fluorescent sensors for temperature or for soft metal ions, such as Ag⁺ and Hg²⁺. With multiple responsiveness integrated in one material, these monodisperse CDs have formed a new class of stimuli-responsive macrocycles, which can reversibly encapsulate and release guest species through multiple switches