Subpicosecond polarized transient-absorption measurements on the fluorescent adenine analogue 2-aminopurine have been performed in the wavelength region from 320 to 690 nm. Global target analysis of the data reveals structural heterogeneity of the chromophore in the excited state. Two distinct states with remarkably different spectroscopic properties were resolved. One state does show stimulated emission, whereas the other state does not and exposes a very long excited-state lifetime. (C) 2003 Elsevier Science B.V. All rights reserved.