Azaindoles are hetero-bicyclic aromatic organic compounds consisting of a pyrrole ring fused to a pyridine ring. Being structurally different from indole only by one additional nitrogen in the six-membered pyridine ring, the azaindole moiety exhibits interesting biochemical and pharmacological activities. Scientists identified that methylated azaindole chromophores could serve as blue or even green fluorescence protein markers. Among various structural isomers of n-azaindole, 7-azaindole derivatives (see Figure for the atom numbering) are excellent blue emitters for organic light-emitting diodes (OLEDs). Figure .