Effect of micelles on the prototropic equilibrium of 2-(4′-N,N-dimethylaminophenyl)pyrido[3,4-d]imidazole

The spectral characteristics of 2-(4'-N,N-dimethylaminophenyl)pyrido[3,4-d]imidazole (DMAPPI) were studied in sodium docecyl sulfate (SDS), cetyltrimethylammonium bromide (CTAB) and Triton X-100 (TX-100) micelles at various acid concentrations. Of the three kinds of monocations (MC1, MC2 and MC3) in DMAPPI, MC1 and MC3 are present in the S-0 state but MC2 and MC3 are present in the S-1 state in SDS. MC2 in SDS, similarly to that in aqueous medium, is formed by biprotonic phototautomerism. In CTAB and TX-100, whereas MC1 and MC2 are present in the aqueous and micellar phase, respectively, MC3 is distributed between both the micellar and aqueous phase in the S-0 state, but only MC2 and MC3 are present in both phases in the S-1 state. MC3 induces micellization of SDS whereas none of the monocation induces micellization of CTAB or TX-100.