The electrochemistry and electrogenerated chemiluminescence (ECL) of two ter(9,9-diarylfluorene)s, TDAFs, were investigated. The ECL from these new blue emitters produced by ion annihilation showed spectra with significant emission at longer wavelengths and was different from their fluorescence spectra. This was ascribed to the formation of excimers. Excimer emission was not observed in ECL during the reduction of the TDAFs with benzoyl peroxide (BPO) as a coreactant, where the ECL spectra were essentially the same as their fluorescence spectra, consistent with the requirement of ion annihilation for excimer production. Excimer emission is not seen in fluorescence, even at relatively high concentrations, because of the short lifetime of 1TDAF*. The quantum yields, φECL, for the ECL by ion annihilation were 0.05% for TDAF-1 and 0.01% for TDAF-2. ECL with BPO as a coreactant produced 8% (TDAF-1) or 3% (TDAF-2) of the ECL intensity of Ru(bpy)32+ generated under the same conditions (0.5 mM TDAF or Ru(bpy)32+/5 mM BPO).