Dual fluorescent compounds are useful platforms for the development of ratiometric probes and sensors. We have developed a new series of dual fluorescent compounds, 1-aryl-substituted 6-methoxy-4-quinolones, and investigated their structural and photophysical properties. The X-ray crystallographic analysis and ab initio quantum chemical calculations revealed that the developed compounds exhibited 60-75 degrees twisted structures. The dual fluorescence of the compounds were observed in polar solvents, and the ratiometric fluorescence responses to alterations in the acidity and temperature were obtained. Copyright (C) 2008 John Wiley & Sons, Ltd.