A hydrogen-bonded network formed between 6-hydroxyquinoline (6-HQ) and acetic acid (AcOH) has been characterized using a time-resolved fluorescence technique. In the bridged hydrogen-bonded complex of cis-6-HQ and AcOH, an excited-state reaction proceeds via proton transfer along the hydrogen bond, resulting in a keto-tautomer (within similar to 200 ps) that exhibits large Stokes-shifted fluorescence. The unbridged complex also undergoes excited-state proton transfer, but the Stokes shift is rather smaller.