Spectral characteristics of the various prototropic species of 2-(4 '-N,N-dimethylaminophenyl)pyrido[3,4-d]imidazole

Spectral characteristics of 2-(4'-N,N-dimethylaminophenyl)pyrido[3,4-d]imid azole (DMAPPI) have been studied in two different solvents and H-0/pH/H- ra nge of -10 to +1.6. Combining the results observed in the absorption, fluor escence,and fluorescence excitation spectra, it is found that (i) only one kind of monoanion (deprotonation of >N-H group) and one kind of trication, (ii) two kinds of monocations (MC1 and MC3) in the ground state and (MC2 an d MC3) in the excited singlet state, and (iii) three kinds of dications (DC 1, DC2, and DC3) are observed. Semiempirical quantum mechanical calculation s (AM1) have been carried out on all kinds of ionic species and their reson ating structures. The spectral characteristics have been assigned to variou s prototropic species combining the experimental and theoretical results.