Unsymmetrical Dendrimers as Highly Efficient Light-Emitting Materials : Synthesis, Photophysics, and Electroluminescence

Highly efficient light-emitting materials can be archived by a rational design that involves rigid dendron and π-conjugated chromophores. This strategy is exemplified by three unsymmetrical dendrimers 5-(2′,3′,4′,5′-tetraphenyl)phenyl-5′-(9- anthracenyl)-2,2′-bithiophene (1), 5-(2′,3′,4′,5′-tetraphenyl)phenyl-5′-(1-pyrenyl)-2,2′ -bithiophene (2), and 5-(2′,3′,4′,5′-tetraphenyl)phenyl-5′-(1-pyrenylethynyl)-2,2′- bithiophene (3). Thermogravimetric analysis and differential scanning calorimetry suggest that unsymmetrical dendrimers 1 and 2 have good thermal stability (>400 °C) and high glass transition temperature (>130 °C) which make them promising candidates for highly stable organic light-emitting devices. The comparative study on their UV−vis absorption and fluorescence spectra in solution and as thin films indicates that the unsymmetrical dendrimers can form intermolecular π−π stacking in the solid state. Electroluminescence (EL) devices using them as emitters were made, and it was found that they emit ...