The proton transfer (PT) emission of the diflavonol molecule 2,8-diphenyl-3,7-dihydroxy-4H,6H-pyrano[3,2-g]chromene-4,6-dione (D3HF) is reported for the first time. The D3HF molecule possesses a chemical structure almost equivalent to two 3-hydroxyflavone molecules symmetrically condensed on one-benzene ring. Thus, D3HF contains two five-membered intramolecular hydrogen bonds (IMHB), and it may undergo double-PT, The discovery via experiments of the D3HF PT emission conforms to the theoretical finding, by using time-dependent (TD) density functional theory (DFT) (with the B3LYP hybrid functional), of a stable single PT tautomer either in the first excited electronic state (S-1) or in the ground electronic state. In the S, state, once the first single PT process occurs, the second one is hindered. (C) 2002 Elsevier Science B.V. All rights reserved.