The electron impact (EI) mass specra of bis(4-dimethylaminopheny1)squaraine 1 and its derivatives 2-14 have been studied. Ions of mass number higher than the molecular ion, which are shown to be precursors of fragment ions of lower mass numbers, are observed. From the structure-property relationship, these ions are assigned to M + CHR1+ and M + Hz1+, where CH2R is the alkyl group in the N,N-dialkylanilino moiety of squaraine. Evidence is provided that the formation of M + CHR1 f and M + Hz1 f. is the result of alkyl transfer and H transfer reactions within a squaraine aggregate rather than intermolecular vapor phase reactions in the mass spectrometer. This molecular aggregate is later shown to be a trimer by analysis of metastable ion data and chemical ionization mass spectrometry. The fragmentation sequence of this trimeric species is elucidated with the assistance of metastable ions. Results show that the trimer may breakdown to monomeric and dimeric species upon electron impact; alternatively, the four-membered ring of the central squaraine in the trimer may cleave to generate two species of approximately equal mass number. These two species usually dominate the mass spectrum and further fragment into M + CHR1 + and M + Hz1 k Detailed fragmentation schemes for M + CHR1 + and M + Hz1 f are proposed and discussed.KOCK-YEE LAW, F. COURT BAILEY et LYNN J. BLUETT. Can. J. Chem. 64, 1607 (1986.On a Ctudit les spectres de masse sous impact Clectronique de la bis(dimCthy1amino-4 phCny1)squaraine (1) [Traduit par la revue]