Regiocontrolled synthesis of poly((3-hexylthiophene-ylene)ethynylenes): Their characterization and photoluminescent properties

A systematically regiocontrolled synthesis of poly((3-hexylthiophene-ylene)ethynylenes) (P3HTEs) is reported. The polymer structures are characterized by H-1 and C-13 NMR spectroscopy. The UV-vis absorption lambda(max) for P3HTE of a head-to-tail chain sequence (5) is slightly higher (about 4 nm) than that of P3HTE 10 with a head-to-head chain sequence. The fluorescence intensity for 5 in the film state, however, is about 10 times stronger than 10 under identical experimental conditions. Both 5 and 10 in solutions exhibit similar structured emissions of high- and low-energy bands. As the conjugation length of the molecule increases, however, the structured emission characteristic appears to be less prominent. The quantum efficiency of P3HTE increases sharply with the conjugation length when the chain length is shorter than the tetramer. Further extending the conjugation length beyond the tetramer appears to shift the fluorescence emission band to a longer wavelength, but to have little effect on the quantum efficiency of the molecule.