The fluorescence of 2,5-bis(benzothiazolyl)hydroquinone was studied for isolated mols. cooled in a supersonic free neon jet. It consists of a strongly Stokes-shifted fluorescence band, and it is assigned to the mol. which is formed by excited-state intramol. proton transfer. The fluorescence excitation spectrum shows a progression in a 114-cm-1 vibrational mode of the excited state. The obsd. spectrum is more congested than that of the parent oxazole under otherwise identical exptl. conditions. The thiazole has no significant intrinsic barrier to excited-state intramol. proton transfer. Weak vibronic bands were obsd. by fluorescence excitation in the adjoining long-wavelength spectral region which could indicate nonvertical transitions to the proton-transferred excited mol.