3 research outputs found
Fluorene–Dithienothiophene-<i>S,S</i>-dioxide Copolymers. Fine-Tuning for OLED Applications
Three groups of fluorene–dithienoÂ[3,2-<i>b</i>;2′,3′-<i>d</i>]Âthiophene-<i>S</i>,<i>S</i>-dioxides (DTT-<i>S</i>,<i>S</i>-dioxide) copolymers, each having four different ratios
of DTT-<i>S</i>,<i>S</i>-dioxide (5, 15, 25, and
50%) were successfully
synthesized through Suzuki coupling method. While the first group
copolymers <b>P1</b> had direct connection of fluorene to the
peripheral thiophenes of DTT-<i>S</i>,<i>S</i>-dioxide, second group copolymers <b>P2</b> had a thiophene
extension between fluorene and DTT-<i>S</i>,<i>S</i>-dioxide, and in the third group, copolymers <b>P3</b>, fluorene
had a connection with DTT-<i>S</i>,<i>S</i>-dioxide
through the phenyl moiety of DTT. Absorbance and emission measurements
of first two groups <b>P1</b> and <b>P2</b> displayed
a regular bathochromic shift with increasing content of DTT-<i>S</i>,<i>S</i>-dioxide, which was more clearly observed
in their solid state fluorescence measurements. Introduction of thiophene
to the peripherals of the DTT-<i>S</i>,<i>S</i>-dioxide in copolymers <b>P2</b> caused even further bathochromic
shift in absorbances and emissions. As the absorbance and emission
of <b>P1</b> went up to 447 and 558 nm in solution, respectively, <b>P2</b> had them at 472 and 592 nm, respectively. In solid state,
emissions of <b>P1</b> and <b>P2</b> even went further
up to 585 and 646 nm, respectively. The bathochromic trend of <b>P1</b> and <b>P2</b> became opposite with absorbance and
solid state emission of <b>P3</b>, which had a hypsochromic
shift with increasing content of DTT-<i>S</i>,<i>S</i>-dioxide. Solid state emission of <b>P3</b>, particularly the
copolymers having 5, 15 and 50% DTT-<i>S</i>,<i>S</i>-dioxide, covered a wide region between 400 and 675 nm. A spread
of colors from light blue (border of white) to red through green and
yellow was obtained with the OLED applications of the copolymers.
Their optical and electronic band gaps varied between 2.17 and 2.99
eV and between 2.68 and 3.57 eV, respectively. While the highest quantum
yield was obtained with <b>P2</b> (5%) as 0.66, the lowest was
observed with <b>P2</b> (50%) as 0.03. Almost all of the polymers
displayed good thermal stabilities. No weight loss was observed with
the copolymers <b>P2</b> (5–15%) and <b>P3</b> up
to 400 °C