Electronic properties of carbazole-fluorene-benzothiadiazole compounds revealed by time resolved spectroscopy and quantum chemistry calculations

► Cz-Fl-Bt compounds have large fluorescence yield. ► Orbital delocalization causes similar spectra of various Cz-Fl-Bt compounds. ► Strong excited state absorption suppresses the stimulated emission. ► Cz-Fl-Bt compounds are not suitable for the light amplification.