2,5‐Functionalized Spiro‐Bisiloles as Highly Efficient Yellow‐Light Emitters in Electroluminescent Devices

New spiro‐bisilole molecules functionalized with nitrogen‐containing heterocyclic groups including 7‐azaindolyl, indolyl, and 2,2′‐dipyridylamino have been synthesized. These molecules are found to display good chemical and thermal stability. They are luminescent in solution and in the solid state with an emission color ranging from blue–green to yellow, depending on the functional group. In the solid state, they display high photoluminescence quantum efficiency (32–40 %). The electroluminescence properties for one of the new molecules, 2,3,3′,4,4′,5‐hexaphenyl‐2′,5′‐bis(p‐2,2′‐dipyridylaminophenyl)spiro‐bisilole, have been investigated by fabricating single‐layer and double‐layer electroluminescent devices. The double‐layer device, in which N,N′‐bis(1‐naphthyl)‐N,N′‐diphenylbenzidine acts as the hole‐transport layer and the functionalized spiro‐bisilole functions as the emitter (emission wavelength = 566 nm) and the electron‐transport layer, displays a brightness of 8440 cd m^–2 at 9 V with a current efficiency of 1.71 cd A^–1. No evidence of exiplex emission is observed.