Synthesis and ordered aggregation in water of a blue light-emitting PEO-PHP-PEO triblock oligomer

Rod-coil block copolymer consists of covalently connected flexible polymer, which tends to adopt random coil conformation, and rigid polymer, which tends to take extended conformation. The phase separation of the immiscible segments can develop to only a limited extent due to the confinement of the linking covalent bond. Because of the competition between phase separation and the trend that rigid rods prefer to orient in a specific direction, rod-coil block copolymer is ready to aggregate regu…

Synthesis and ordered aggregation in water of a blue light-emitting PEO-PHP-PEO triblock oligomer

A novel blue light-emitting coil-rod-coil triblock oligomer, PEO-PHP-PEO, which consists of para-hexaphenyl (PHP) as the rigid rod and poly(ethylene oxide) (PEO, M w = 750) as the flexible coil, has been synthesized. It is the first soluble poly(para-phenylene) molecule containing no lateral substituent, which can dissolve not only in organic solvents such as chloroform and THF, but also in water. The critical micelle concentration (CMC) of PEO-PHP-PEO in water is 5.25×10-4 mol@L-1 and the surface tension at CMC, γCMC, is 61.29 mN@m-1. The absorption peak of the molecularly dissolved PEO-PHP-PEO in water is centered at 323 nm and the fluorescence spectrum has a maximum at 432 nm and shows the vibronic fine structure typical of molecular dissolution. The photoluminescence spectrum of the aggregate solution is similar to that of the PHP polycrystal film, indicating that the ordered packing of PHP block has taken place due to a combination of hydrophobic interaction and π-π Stacking. The oligomer self-assembles into cotton-like nanofibers with diameter of about 20 nm in 5.0×10-3 mol@L-1 aqueous solution.