Science Concentrates POLYMERS
CREDIT: NAT. NANOTECHNOL. (MICROGRAPH); ACS BIOMATER. SCI. ENG. (HAIR)
▸ Iminoborane units add inorganic flavor to polymers Chemists in Germany have reported a novel inorganic–organic hybrid polymer that can be regarded as an amino borane analog of poly(p-phenylene vinylene), a semiconducting polymer commonly used in light-emitting diodes, field-effect transistors, solar cells, and other optoelectronic devices (Angew. Chem. Int. Ed. 2017, DOI: 10.1002/anie.201612476). Researchers are increasingly taking advantage of the technique of substituting selected C≥C units in conjugated organic frameworks with structurally equivalent B≥N units to create materials with new properties n and functions. Because Poly(p-phenylene π-electron conjugation is often disrupted vinylene) when substituting B≥N for C≥C, Holger R Helten and coworkers B of RWTH Aachen University became curious N n whether they could R create a BN analog Poly(p-phenylene of poly(p-phenylene vinylene) and whether iminoborane) the polymer’s π-conjugation would persist. The researchers prepared the BN analog, poly(p-phenylene iminoborane), by a polycondensation reaction of boron- and silylamine-disubstituted benzenes. The team’s photophysical studies on the polymer and a series of oligomers provided evidence of π-conjugation across the B≥N linkages, although it is less pronounced than for all-carbon poly(p-phenylene vinylene). The Aachen researchers are now further exploring the concept of BN doping of conjugated polymers with an eye toward developing new organic electronics applications.—STEVE RITTER
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Triangulene trapped Chemists have been dreaming of triangulene since the 1950s. That’s when Erich Clar, the University of Glasgow chemist considered the father of modern polycyclic aromatic chemistry, first proposed the structure for the C22H12 molecule, also known as Clar’s hydrocarbon. Despite triangulene’s even numbers of carbons and electrons, it is connected in such a manner that all of its electrons are impossible to pair up. Consequently, two electrons sit unpaired, making the molecule an extremely reactive biradical, as Clar discovered when he tried to synthesize it. Scientists at IBM Research, Zurich, and the University of Warwick now report the first synthesis and characterization of triangulene (Nat. Nanotechnol. 2017, DOI: 10.1038/nnano.2016.305). The researchers, led by IBM’s Niko Pavliček, made triangulene one molThis atomic force microscope ecule at a time by placing a dihydroimage reveals triangulene on a triangulene precursor on a copper, copper surface. xenon, or NaCl surface and then using the probe tip of a combined scanning tunneling and atomic force microscope to shoot electrons at it until they knocked off two hydrogens, thereby generating triangulene. Pavliček and coworkers were surprised to discover that triangulene did not bond to the copper surface, possibly because its unpaired electrons are in π orbitals and are perpendicular to the metal surface.—BETHANY HALFORD
population, but these products can be prob- found. They suspected that getting more lematic, say researchers led by Jong-Rok synthetic melanin from the liquid dye to Jeon of South Korea’s Gyeongsang National solid hair strands would help gray hair go University. For instance, many dyes use back to black, and they found iron was espep-phenylenediamine for its ability to pencially effective at recruiting polydopamine. etrate hair and help provide long-lasting Iron chelates polydopamine clusters with color. But the molecule is also a skin irritant one another and appears to bind the polythat may lead to hair loss, the researchers mer’s amine and catechol groups to hair’s explain. They thought dyes using polydopa- keratin (ACS Biomater. Sci. Eng. 2017, DOI: mine particles would be safer alternatives 10.1021/acsbiomaterials.7b00031). The because of the synthetic polymer’s similarresulting black dye can withstand repeated ity to natural melanin pigments found in washings, and mice exposed to it daily for dark hair. Pure polydo16 days all lived and pamine does dye human Gray hairs donated by a cosmetic kept their hair—unlike gray hair samples but company (left) are colored by most test mice colored not to the deep shades polydopamine alone (center) with p-phenylenedidesired by Korean conbut fully blackened by an ironamine dye.—MATT sumers, the researchers polydopamine combo (right). DAVENPORT
▸ Looking for a safer way to dye A touch of gray may suit some people, but many others are grateful for dyes that return hair to its natural color. For example, black dyes made with small organic molecules are popular among Asia’s graying FEBRUARY 20, 2017 | CEN.ACS.ORG | C&EN
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