From C&EN, via nature.com

A new set of organic molecules might be able to bring us brighter screens for the many technologies we use today. From C&EN:

Researchers in Japan have designed and synthesized low-cost compounds based on carbazolyl dicyano­benzene (CDCB) and show they efficiently emit light in response to an electric current (Nature, DOI:10.1038/nature11687). The family members, which differ in the number of carbazolyl units and the presence of other organic substituents, emit a wide spectrum of colors ranging from sky blue to orange.

The earliest OLED displays, introduced roughly 25 years ago, were based on all-organic fluorescent materials that inherently convert just a small fraction of electrical energy input to light. OLEDs featuring phosphorescent metal-organic compounds proved to be more efficient emitters, and they are now the standard in this area. Yet they are costly because they include rare metals such as iridium and depend on exotic metal catalysts for their synthesis.

By tailoring the structure of compounds that include electron-donating carbazole groups and electron-accepting dicyanobenzene units, Kyushu University chemists Chihaya Adachi and Hiroki Uoyama and coworkers have now designed metal-free compounds with a tiny energy gap between the molecules’ excited singlet and triplet electronic states. The low-cost, all-organic compounds were made in one step from commercially available starting materials. Because of their electronic structures, the compounds exhibit electroluminescent efficiencies comparable to today’s best phosphorescent OLEDs.