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, ãCMC, 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.