Spectral characteristics of 2-(4'-N,N-dimethylaminophenyl)pyrido[3,4-d]imidazole in AOT/n-heptane/water reverse micelles.

Spectral characteristics of 2-(4'-N,N-dimethylaminophenyl)pyrido[3,4-d]imidazole (DMAPPI) have been studied in AOT/n-heptane/water reverse micelles at w0 > or = 0. Absorption, fluorescence excitation and fluorescence spectra have revealed that the monocation (MC) of DMAPPI, protonated at the imidazole nitrogen (MC2) (Scheme 2) is present in the S0 state at w0 = 0, along with the MC, protonated at pyridine nitrogen (MC3) and only normal emission is observed from both MC2 and MC3. With increase in w0 (water amount), the equilibrium is shifted towards the MC, protonated at -NMe2 group (MC1) and MC3 in the S0 state. Biprotonic phototautomerism is observed in MC1 to generate MC2 in the S1 state. The twisted intramolecular charge transfer (TICT) emission replaces the normal emission in MC3. All the MCs are present near the anionic polar head group of AOT in the bound water region.