Bathocuproine (CAS No. 205-805-8; Chemical Formula: C₂₆H₂₀N₂) is an organic heterocyclic compound known as 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline. It is a yellow crystalline solid primarily used as a selective colorimetric reagent for detecting copper(I) ions and as an electron-transport material in OLEDs and photovoltaic devices.