Synthesis and chiroptical properties of poly(p-phenylenevinylene-alt-m-phenylenevinylene) bearing (-)-trans-myrtanoxyl groups on the p-phenylene rings

Chiral poly(p-phenylenevinylene-alt-m-phenylenevinylene)s bearing (-)-trans-myrtanoxyl groups on the p-phenylene rings were synthesized by Wittig's reaction and Heck's reaction, respectively, namely Myr-PMPV-w and Myr-PMPV-h correspondingly. The chiroptical properties of the polymers were investigated in chlorobenzene solution by circular dichroism. The results showed that both Myr-PMPV-w and Myr-PMPV-h showed no Cotton effect due to their irregular molecular structure. By the treatment with I-2, most of the cis-vinylene linkages in Myr-PMPV-w were converted to trans-vinylenes, consequently, the structure of Myr-PMPV-w became much more regular, and the resulting polymer (iso-Myr-PMPV-w) showed strong bisignate Cotton effects in the pi-pi* transition. Compared to its analogous poly(p-phenylenevinylene) (PPV) (iso-Myr-PPV-w), iso-Myr-PMPV-w showed much stronger Cotton effect, its maximum g value was about one order of magnitude higher than that of iso-Myr-PPV-w under the same conditions. With increasing concentration and decreasing temperature, the g(max) value of iso-Myr-PMPV-w increased, and the maximum absorption was slightly blue-shifted, but the shape and range of absorption curves did not changed significantly, and no clear isosbestic point could be observed. (C) 2008 Wiley Periodicals, Inc.