Advanced Functional Materials, Vol.19, No.18, 2978-2986, 2009
Electroluminescence and Laser Emission of Soluble Pure Red Fluorescent Molecular Glasses Based on Dithienylbenzothiadiazole
Soluble molecular red emitters 1a/1b are synthesized by Stifle coupling from 2-(3,5-di(1-naphthyl)phenyl)thiophene precursors. The compounds show emission maxima at ca. 610 nm in CH2Cl2 solution and 620 nm in solid films. Replacing the n-hexyl substituent by 4-sec-butoxyphenyl produces a marked increase of glass transition temperature (T-g) from 82 degrees C to 137 degrees C and increases the solubility in toluene and p-xylene, thus improving to film-forming properties. Cyclic voltammetry shows that the compounds can be reversibly oxidized and reduced around +1.10 and -1.20V, respectively. A two-layered electroluminescent device based on 1b produces a pure red light emission with CIE coordinates (0.646, 0.350) and a maximal luminous efficiency of 2.1 cd A(-1). Furthermore, when used as a solution-processed red in optically pumped laser devices, compound 1b successfully produces a lasing emission at ca. 650 nm.