Electronic Spectroscopy of Maleimide and Its Isoelectronic Molecules. I. Maleimide and N-Alkylmaleimides

Abstract

The electronic absorption spectra of maleimide and two N-alkylmaleimides are presented. Molecular-orbital classifications of four electronic transitions with energies 〈 6.5 eV are made for maleimide. Vibrational structure appearing in two of the transitions in the N-alkylmaleimides in the vapor phase is interpreted and assignments of the active vibrational modes discussed. A series of hot bands derived from the 2000-Å band of N-methylmaleimide is analyzed and employed in the association of the corresponding active ground- and excited-state vibrational modes. The vacuum-ultraviolet vapor absorption spectrum of N-methylmaleimide is presented. Phosphorescence emissions from maleimides in glassy media at 77°K suggest that the T1 states of these molecules are Γ n π*3.