Studies of the Photochemistry of Aromatic Diazo Compounds. III. The Electronic Structures of Some m-Substituted Benzenediazonium Cations

The electronic structures and electronic absorption spectra of m-fluoro-, m-chloro-, m-bromo-, and m-methoxybenzenediazonium cations were studied by making molecular orbital calculations, and by measuring the near-ultraviolet absorption spectra. From the calculations it is understood that when an electron-donating group is introduced at the m-position of the benzenediazonium cation, a mixing of the lowest locally-excited 1B1 state within the benzenediazonium cation and the intramolecular charge-transfer state arising from the electron transfer from the electron-donating group at the m-position to the lowest unoccupied molecular orbital of the benzenediazonium framework comes to show a large contribution of the substituted cation in the lowest excited state while at the same time the energy of the corresponding state is lowered. The ground and the excited 1A1 states of the nonsubstituted cation are not so greatly affected by the m-substitution as is the 1B1 state. The degree of the mixing of the 1A1 and 1B...